CST 205 Object Oriented Programming using Java PDF

CST 205 Object Oriented Programming using Java CST 281 Object Oriented Programming (As per KTU 2019 Syllabus) Course overview & Module 1 Downloaded from Ktunotes.in Overview 4 credit course Prerequisite: Topics covered under the course PROGRAMMING IN C (ES...

CST 205 Object Oriented Programming using Java CST 281 Object Oriented Programming (As per KTU 2019 Syllabus) Course overview & Module 1 Downloaded from Ktunotes.in Overview 4 credit course Prerequisite: Topics covered under the course PROGRAMMING IN C (EST102) Continuous Internal Evaluation Pattern: ○ Attendance : 10 marks ○ Continuous Assessment Tests : 25 marks ○ Continuous Assessment Assignments : 15 marks Practice - [CS205/CS281] complete all the exercises uploaded in Virtual Programming Lab URL to Virtual Lab: http://34.87.58.133/ Prefered mode of communication : Post your queries in Google Classroom or Whatsapp message. Downloaded from Ktunotes.in Course Outcomes CO1 - Write Java programs using the object oriented concepts - classes, objects, constructors, data hiding, inheritance and polymorphism [Apply] CO2 - Utilise data types, operators, control statements, built in packages & interfaces, Input/Output Streams and Files in Java to develop programs [Apply] CO3 - Illustrate how robust programs can be written in Java using exception handling mechanism [Understand] CO4 - Write application programs in Java using multithreading and database connectivity [Apply] CO5 - Write Graphical User Interface based application programs by utilising event handling features and Swing in Java [Apply] Downloaded from Ktunotes.in Assessment Pattern Downloaded from Ktunotes.in  Modules Module Contents No. of lectures planned 1 Approaches to Software Design, OOD, UML, Java introduction 6 2 Primitive Data types, Operators, Class Fundamentals, Inheritance 9 3 Packages, Interfaces, Exception handling, Input/Output 7 4 Java Library, Collection Framework, Event handling, Multithreading 9 5 Graphical User Interface and Database support 7 Minimum number of lectures : 38~45 Downloaded from Ktunotes.in  Text books Reference text 1. Herbert Schildt, Java: The Complete Reference, 8/e, Tata McGraw Hill, 2011. 2. Rajib Mall, Fundamentals of Software Engineering, 4th edition, PHI, 2014. 3. Paul Deitel, Harvey Deitel, Java How to Program, Early Objects 11th Edition, Pearson,2018 Downloaded from Ktunotes.in Module 1 ► Approaches to Software Design. Functional Oriented Design, Object Oriented Design, Case Study of Automated Fire Alarm System ► Object Modeling Using Unified Modeling Language. Basic Object Oriented concepts, UML diagrams, Use case model, Class diagram, Interaction diagram, Activity diagram, State chart diagram ► Introduction to Java - Java programming Environment and Runtime Environment,, Development Platforms - Standard, Enterprise. Java Virtual Machine, Java compiler, Bytecode, Java applet Java Buzzwords, Java program structure, Comments, Garbage Collection, Lexical Issues https://www.youtube.com/channel/UCTBjhZB3ni3_NCT9M0XNOpQ Downloaded from Ktunotes.in What is software? Software is a set of instructions, data or programs used to operate computers and execute specific tasks Software is a set of instructions that tell a computer what to do. Without software, most computers would be useless. For example, without your Internet browser software, you could not surf the Internet. Without an operating system, you cannot even login to your system. The term was coined to differentiate these instructions from hardware. By the term software, we referring to all variants such as Middleware, O.S, Firmware etc. Downloaded from Ktunotes.in  Types of software There are two types of software 1. System Software 2. Application Software Examples of system software are Operating System, Compilers, Interpreter, Assemblers, etc. Examples of Application software are Railways Reservation Software, Microsoft Office Suite Software, Microsoft Word, etc. Downloaded from Ktunotes.in Software Design Software design is a process to transform user requirements into some suitable form, which helps the programmer in software coding and implementation. Software design is the process by which an agent creates a specification of a software artifact, intended to accomplish goals, using a set of primitive components and subject to constraints. Downloaded from Ktunotes.in Software Design The design process for software systems often has two levels. At the first level the focus is on deciding which modules are needed for the system on the basis of SRS (Software Requirement Specification) and how the modules should be interconnected. It tries to specify how to fulfill the requirements mentioned in SRS document. Downloaded from Ktunotes.in Approaches to Software Design There are two generic software development approaches. Downloaded from Ktunotes.in Function Oriented Design (FOD) Global variables FOD is an approach to software design where the design is decomposed into a set of interacting units where each unit has a clearly defined function. This design mechanism divides the whole system into smaller functions Starting at this high level view of the system, each function is successively refined into more detailed functions The system state is centralized and shared among different functions Top down approach Downloaded from Ktunotes.in  Function Oriented Design (FOD) At first FOD views a system as a black-box that provides a set of services to the users of the software. These services provided by a software to its users are also known as the high-level functions supported by the software. During the design process, these high-level functions are successively decomposed into more detailed functions. The term top-down decomposition is often used to denote the successive decomposition of a set of high-level functions into more detailed functions. Downloaded from Ktunotes.in  Functional Oriented Design (FOD) These functional modules can share information among themselves by means of information passing and using information available globally. Eg: Banking process Here withdraw, deposit, transfer are functions and that can be divided into subfunctions again. So, in FOD, the entire problem is divided in to number of functions and those functions are broken down into smaller functions and these smaller functions are converted in to software modules. Downloaded from Ktunotes.in Object Oriented Design (OOD) OOD is based on Objects and interaction between the objects. Interaction between objects is called message communication. In the object-oriented design approach, the system is viewed as a collection of objects (i.e. entities). It involves the designing of objects, classes and the relationship between the classes The state is decentralized among the objects and each object manages its own state information. OOD follows bottom up approach Consider the example of Banking process. Here, customer, money and account are objects Downloaded from Ktunotes.in Object Oriented Design (OOD) For example, in banking example,each customer may be a separate object with its own data and functions to operate on these data. Functions defined for one object cannot refer or change data of other objects. Objects have their own internal data which define their state. Similar objects constitute a class. In other words, each object is an instance of some class. Classes may inherit features from super class. Conceptually, objects communicate by message passing. Downloaded from Ktunotes.in FOD vs OOD Downloaded from Ktunotes.in Case study: Automated fire alarm The owner of a large multi-storied building wants to have a computerized fire alarm system for his building. Smoke detectors and fire alarms would be placed in each room of the building. The fire alarm system would monitor the status of these smoke detectors. Whenever a fire condition is reported by any of the smoke detectors, the fire alarm system should determine the location at which the fire condition is reported by any of the smoke detectors, the fire alarm system should determine the location at which the fire condition has occurred and then sound the alarms only in the neighboring locations. The fire alarm system should also flash an alarm message on the computer console. Fire fighting personnel, man the console round the clock. After a fire condition has been successfully handled, the fire alarm system should support resetting the alarms by the fire fighting personnel. Downloaded from Ktunotes.in FOD: Automated fire alarm Downloaded from Ktunotes.in OOD: Automated fire alarm END OF LECTURE 1 Downloaded from Ktunotes.in Basic Object Oriented Concepts In OOD, implementation of a software is based on the concepts of objects. This approach is very close to the real-world applications Downloaded from Ktunotes.in Class & Object CLASS A class is a blueprint or prototype from which objects are created A class is a generalized description of an object. No physical existence. Acts as a type or category. OBJECT An object is an instance of a class Objects are real-world entities that has their own state and behavior. An object has physical existence Downloaded from Ktunotes.in Class & Object Let’s take Student as a class. James is an instance / object of the class Student Object has a physical existence while a class is just a logical definition. State => Variables Name RollNo Behaviors => Functions setName() setRollNo() Downloaded from Ktunotes.in Abstraction Abstraction means displaying only essential information and hiding the internal details. It is a process of generalizing things at design level. Data abstraction refers to providing only essential information about the data to the outside world, hiding the background details or implementation. Consider a real-life example of a man driving a car. The man only knows that pressing the accelerators will increase the speed of the car or applying brakes will stop the car. All about showing necessary details. Downloaded from Ktunotes.in  Encapsulation The wrapping up of data(variables) and functions (methods) that operates on the data, into a single unit (called class) is known as encapsulation. It is also called "information hiding“, hides the internal representation, or state, of an object from the outside through access modifies (Private / Public). Hiding unnecessary details, at implementation level. Downloaded from Ktunotes.in  Encapsulation... Protection of data from accidental corruption, by means of access specifiers (Private / Public), it provides security. Flexibility and extensibility of the code and reduction in complexity Encapsulation of a class can hide the internal details of how an object does something Encapsulation protects abstraction Downloaded from Ktunotes.in Abstraction & Encapsulation Downloaded from Ktunotes.in Inheritance The capability of a class to derive properties and characteristics from another class is called Inheritance. Inheritance is the process by which objects of one class acquired the properties of objects of another classes Base Class : The class whose properties are inherited by subclass is called Base Class or Super class. Derived Class : The class that inherits properties from another class is called Subclass or Derived Class. Downloaded from Ktunotes.in Inheritance Reusability: Inheritance supports the concept of “reusability”, i.e. when we want to create a new class and there is already a class that includes some of the code that we want, we can derive our new class from the existing class. By doing this, we are reusing the fields and methods of the existing class. Downloaded from Ktunotes.in Types of Inheritance Downloaded from Ktunotes.in  Polymorphism The word polymorphism means having many forms. Refers to a programming language's ability to process objects differently depending on their data type or class An operation may exhibit different behaviors in different instances. The behavior depends upon the types of data used in the operation. Ability for objects of different classes related by inheritance to respond differently to the same member function call Downloaded from Ktunotes.in Polymorphism... Static polymorphism: the binding between the method call an the method body happens at the time of compilation and, this binding is known as static binding or early binding Runtime polymorphism or Dynamic Method Dispatch is a process in which a call to an overridden method is resolved at runtime. Dynamic binding happens when all information needed for a function call cannot be determined at compile-time In the example, same rotation of steering wheel causes, different mechanical operations, corresponding to the steering type present in each cars. Brings flexibility to the implementations Downloaded from Ktunotes.in  Association, Composition and Aggregation Association is relation between two separate classes which establishes through their Objects. Association can be one-to-one, one-to-many, many-to-one, many-to-many. Aggregation is a special form of Composition: It represents part-of relationship. Association where: In composition, both the entities are dependent It represents Has-A relationship. on each other. It is a unidirectional association When there is a composition between two In Aggregation, both the entries can entities, the composed object cannot exist survive individually. without the other entity. Downloaded from Ktunotes.in OO concepts review ENDfrom Downloaded OF LECTURE 2 Ktunotes.in  Unified Modeling Language (UML) UML (Unified Modeling Language) is a general-purpose, graphical modeling language in the field of Software Engineering Developed to help system and software developers for specifying, visualizing, constructing, and documenting the artifacts of software systems UML was created by the Object Management Group (OMG) UML is not a programming language, it is rather a visual language. UML is a visual language for developing software blueprints (designs). For example, while constructing buildings, a designer or architect develops the building blueprints. Similarly, we can also develop blueprints for a software system. Downloaded from Ktunotes.in Unified Modeling Language (UML) UML is the most commonly and frequently used language for building software system blueprints UML can be used for business modeling and other non software systems In UML there are a lot of different diagrams to get used to. The reason for this is that it is possible to look at a system from many different viewpoints of the stakeholders. A software development will have many stakeholders playing a part ○ Analysts ○ Designers ○ Coders ○ Testers ○ Quality Assurance ○ The Customer ○ Technical Authors Downloaded from Ktunotes.in UML Diagrams UML is linked with object oriented design and analysis Structure Diagrams : Capture static aspects or structure of a system Behavior Diagrams: Capture dynamic aspects or behavior of the system Downloaded from Ktunotes.in Downloaded from Ktunotes.in Use Case Diagram A UML use case diagram is the primary form of system/software requirements. It is a behavior diagram to illustrate a set of actions or use cases that a system can perform in tandem with one or more external users of the system (actors) The purpose of a use case diagram in UML is to demonstrate the different ways that a user might interact with a system. It is an effective technique for communicating system behavior in the user's terms by specifying all externally visible system behavior. It does not show the order in which steps are performed to achieve the goals of each use case. Use case diagrams are typically developed in the early stage of development ○ Developed by analysts together with domain experts to gather the requirements of a system. ○ Identify the external and internal factors influencing the system. ○ Show the interaction among the requirements and actors ○ Can be used to validate a systems architecture ○ Drive implementation and generate test cases Downloaded from Ktunotes.in Is it really needed? Downloaded from Ktunotes.in Use Case Diagram - Actor Represent “stick man” icon. One actor can be associated with multiple use cases in the system Actor is someone who interacts with use case (system function). Actor is an outsider to the system boundary who plays a role in the operating the system/business. Actor triggers use case(s). Actor is not an insider to the system. Actor has a responsibility toward the system (inputs), and Actor has expectations from the system (outputs). Downloaded from Ktunotes.in  Use Case Diagram - Use case Horizontally shaped ovals that represent the different uses that a user might have A use case represents a distinct functionality of a system, a component, a package, or a class Represents a system function (automated or manual) Each Actor must be linked to a use case, while some use cases may not be linked to actors. Downloaded from Ktunotes.in  Structuring use case diagrams with relationship There can be 5 relationship types in a use case diagram. 1. Association between actor and use case 2. Generalization of a use case 3. Generalization of an actor 4. Extend between two use cases 5. Include between two use cases Downloaded from Ktunotes.in Use Case Diagram - Association A line between actors and use cases The participation of an actor in a use case is shown by connecting an actor to a use case by a solid link. An actor must be associated with at least one use case Actors may be connected to use cases by associations, indicating that the actor and the use case communicate with one another using messages. UML allows the use of multiplicity (cardinality) at one or both ends of association between the actor and the use case Downloaded from Ktunotes.in Generalization of an Actor Generalization of an actor means that one actor can inherit the role of the other actor. The descendant inherits all the use cases of the ancestor. The descendant has one or more use cases that are specific to that role. In the example, how many use cases are there for NFRC customer? Downloaded from Ktunotes.in Use case Generalization A use-case-generalization is a directed relationship from a child use case to a parent use case, specifying how a child can specialize all behavior and characteristics described for the parent A parent use case may be specialized into one or more child use cases that represent more specific forms of the parent. Neither parent nor child is necessarily abstract, although the parent in most cases is abstract. A child inherits all structure, behavior, and relationships of the parent. Downloaded from Ktunotes.in Extend relationship between two use cases Extend is a directed relationship that specifies how and when the behavior defined in extending (optional) use case can be inserted into the the extended use case. The extending use case is dependent on the extended (base) use case. The extended (base) use case must be meaningful on its own. The optional extending use case is triggered conditionally at an extension point. An extension point is a feature of an extended use case, by which it decides to extend its functionality by inserting the extending use case. Extension points may be shown in a compartment of the use case oval symbol under the heading extension points. Each extension point must have a name. Downloaded from Ktunotes.in  Include relationship between two use cases Use case include is a directed relationship between two use cases which is used to show that behavior of the included use case is inserted into the behavior of the including use case Include relationship show that the behaviour of the included use case is part of the including (base) use case. The main reason for this is to reuse the common actions across multiple use cases and to simplify complex use cases. The base use case is incomplete without the included use case. The included use case is mandatory and not optional. Downloaded from Ktunotes.in Use Case Diagram - System boundary An optional box that sets a system scope to use cases. All use cases outside the box would be considered outside the scope of that system. If no box is given, all use cases are within the system scope. The system boundary is potentially the entire system as defined in the requirements document. For large and complex systems, each module may be the system boundary. Downloaded from Ktunotes.in Use case diagram - Packages Packages are optional UML constructs that enable you to organize model elements (such as use cases) into groups. Packages are depicted as file folders and can be used on any of the UML diagrams, including both use case diagrams and class diagrams Downloaded from Ktunotes.in Business Use Case modeling notations Support for business modeling is declared as a goal of UML, but UML specification does not provide any notations for business use cases. Business use cases were introduced in Rational Unified Process (RUP). Business use case should produce a result of observable value to a business actor. Defines what happens in the business when the use case is requested by business actor, it describes complete workflow or business process. Business use case is represented in RUP with use case oval and a line crossing it. Business Actor is represented in RUP by "stick man" icon with a line crossing its head. Not defined in UML specification. Downloaded from Ktunotes.in Use case diagram of a Hospital Management System Downloaded from Ktunotes.in  END Downloaded OF LECTURE from 3 Ktunotes.in Class Diagram Class diagram in the UML is a type of static structure diagram to represent the design of the software system in terms of classes and their relationships.. It shows the structure of a system at the level of classes and interfaces, along with their attributes, operations, and the relationships among objects. There are several software tools available create UML Class diagrams. Rational rose, StarUML and Lucidchart are some of the popular tools. Some common types of class diagrams are: 1. Domain Model Diagram - representation of real-world conceptual classes (contains only attributes), not of software components, to understand the project domain. 2. Implementation Classes Diagram - representation of the structure of software components, describes classes, interfaces, associations, usage, realization. Downloaded from Ktunotes.in  UML notation for Class A class notation consists of three parts: 1. Class Name (mandatory): ○ The name of the class appears in the first partition. 2. Class Attributes[optional]: ○ An attribute is a named property of a class that describes the object being modeled ○ Attributes are shown in the second partition. ○ The attribute type is shown after the colon. ○ Derived attribute is designated by a preceding ‘/’ ○ Attributes map onto member variables (data members) in code. 3. Class Operations(Methods)[optional]: ○ Operations are shown in the third partition. They are services the class provides. ○ The return type of a method is shown after the colon at the end of the method signature. ○ Operations map onto class methods in code Downloaded from Ktunotes.in  Member visibility Visibility defines whether attributes and operations of specific classes can be seen and used by other classes UML has 4 types of visibility and it is represented by prefixing a literal( +, -, #, ~) Downloaded from Ktunotes.in Member visibility PRIVATE PROTECTED DEFAULT / PACKAGE PUBLIC Downloaded from Ktunotes.in  Member scope The UML specifies two types of scope for members: instance and classifier. Classifier members are commonly recognized as “static” in many programming languages. The scope is the class itself. ○ All the instances share the classifier scoped members. To indicate a classifier scope for a member, its name must be underlined. Otherwise, instance scope is assumed by default. Instance members are scoped to a specific instance. ○ Each instantiated object of the class has its own copy of the instance members. Downloaded from Ktunotes.in Relationships between classes Relationships in class diagrams include different types of logical connections. Downloaded from Ktunotes.in  Relationships between classes 1. Association Represents static relationships between two classes. Shows that instances of classes could be either linked to each other or combined logically or physically. Represented by a solid line (with or without open arrow) connecting two classes 2. Dependency A dependency means the relation between two or more classes in which a change in one may force changes in the other. Dependency indicates that one class depends on another. A dashed line with an open arrow Downloaded from Ktunotes.in Relationships between classes 4. Aggregation A special type of association to represent a "has a" relationship eg. Team has 9 players A solid line with an unfilled diamond at the association end connected to the class of composite 5. Composition A special type of aggregation where parts are destroyed when the whole is destroyed. No independent existence A solid line with a filled diamond at the association connected to the class of composite Downloaded from Ktunotes.in Relationships between classes 6. Generalization (Inheritance) A generalization helps to connect a subclass to its superclass. A sub-class is inherited from its superclass. A solid line with a hollow arrowhead that point from the child to the parent class 7. Realization (Implements) Realization relationship is a relationship between two model elements, in which one model element (the client) realizes (implements or executes) the behavior that the other model element (the supplier) specifies. Downloaded from Ktunotes.in Relationships between classes Multiplicity Multiplicity defines how many objects participate in a relationship and it is the number of instances of one class related to one instance of the other class. Multiplicity is represented as a number and a * is used to represent a multiplicity of many Downloaded from Ktunotes.in Class diagram for a Pizza Order system Downloaded from Ktunotes.in  Interaction Diagrams Interaction diagrams capture the dynamic behavior of the system An interaction is a set of messages that are interchanged between the entities to achieve certain specified tasks in the system. Represents the interactions between distinct entities present. It is used in UML to establish communication between objects. Mostly focus is on message passing and how these messages make up one functionality of the system. The details of interactions can be shown using different UML diagrams. a. Sequence diagram. b. Collaboration(communication) diagram. c. Timing diagram d. Interaction overview diagram Downloaded from Ktunotes.in  Different types of Interaction Diagrams 1. Sequence diagram Shows object interactions arranged in time sequence. Focus is on the sequence of messages exchanged. 2. Collaboration(communication) diagram Shows the interaction between the objects to fulfill the functionality of a use case. This diagram is suitable to depict the relationship between the objects. 3. Timing diagram Focus is on the instance at which a message is sent from one object to another object. Suitable to represent the state transitions of the objects. 4. Interaction overview diagram - Sequence Diagram + Activity Diagram Downloaded from Ktunotes.in  1. Sequence Diagram The purpose of a sequence diagram in UML is to visualize the sequence of a message flow in the system A Sequence Diagram simply depicts interaction between objects in a sequential order. Lifelines, Activations and Messages are the key notations in a sequence diagram. Using fragment operators, iteration and branching can be represented in sequence diagram. 1. Lifeline A lifeline represents a single participant in an interaction. It is represented by a vertical bar, with a rectangle containing its object name (name is optional, format object_name : class_name). The vertical axis represents time proceedings Describes how an instance participates in the interaction Downloaded from Ktunotes.in  Activation & Messages 2. Activations A thin rectangle on a lifeline, represents the period during which an element is performing an operation. The top and the bottom of the of the rectangle are aligned with the initiation and the completion time respectively 3. Messages Communication between objects(lifelines) is represented using messages. The messages appear in a sequential order on the lifeline. Downloaded from Ktunotes.in  Synchronous vs Asynchronous A synchronous message waits for a reply before the interaction can move forward. The sender waits until the receiver has completed the processing of the message. A solid arrow head to represent a synchronous message. An asynchronous message does not wait for a reply from the receiver. The interaction moves forward irrespective of the response for previous message. A solid line with open arrow head represents an asynchronous message. Downloaded from Ktunotes.in Other messages used A message defines a particular communication between Lifelines. 1. Call Message Call message is a kind of message that represents an invocation of operation of target lifeline. 2. Return Message Return message is a reply from the target lifeline for a previous message. Represented with dashed line with an open arrowhead Downloaded from Ktunotes.in Other messages used 3. Self Message Self message is a kind of message that represents the invocation of message of the same lifeline. 4. Recursive Message A self message sent for recursive purpose is called a recursive message. It's target points to an activation on top of the activation where the message was invoked from. Downloaded from Ktunotes.in  Other messages used 5. Create Message / Constructor Message Create message is a kind of message that represents the creation of (target) lifeline. It creates the message receiver 6. Destroy Message / Destructor Message Destroy message is a kind of message that represents the request of destroying the target lifeline. It destroys the message receiver. 7. Duration Message / non-instantaneous message Duration message shows the time delay between the send time and receive time of the message. (eg, network communication delay) Downloaded from Ktunotes.in Messages used 8. Found message - Unknown sender A Found message is used to represent a scenario where an unknown source sends the message. 9. Lost message - Unknown receiver A Lost message is used to represent a scenario where the recipient is not known to the system. Downloaded from Ktunotes.in Combined fragments Fragment is represented as a transparent window or box, divided by horizontal dashed lines for each operand. A combined fragment, has a fragment operator, [guard text] and one or more operands which encloses a portion of the interactions within a seq. diagram. Operands are separated by dashed line and each operand encloses one or more messages, interaction uses, or combined fragments. Fragment operator is in the top left corner of the box and it indicates the type of fragment such as loop, break, alt, opt…Corresponding to the operator, interaction constraints or guard is represented in [...] Sample interaction use Downloaded from Ktunotes.in Types of fragment operators Downloaded from Ktunotes.in Sample Sequence Diagram - Place Order Scenario The item ordered will be sent to the member either send by courier or by ordinary mail depending on membership type. Optionally, the shop will send the member a confirmation notification. Downloaded from Ktunotes.in Example - Sequence Fragments Downloaded from Ktunotes.in  Notes on Sequence Diagrams Advantages Sequence diagrams are easier to maintain and easier to generate. Represent the low level details of a UML use case. Model the logic of a complex procedure, function, or operation. Shows the interaction between the objects and components to complete a process. Disadvantages Can be complex when too many lifelines are involved in the system. If the order of message sequence is changed, then incorrect results are produced. The type of message decides the type of sequence inside the diagram Each sequence needs to be represented using different message numbering schemes, which can be a little complex in large systems. Downloaded from Ktunotes.in  2. Communication Diagram Communication (in UML 2. x, earlier name - Collaboration) Diagrams are used to show how objects interact to perform the behavior of a particular use case, or a part of a use case. Collaboration represents the relationships and interactions among software objects. They are used to understand the object architecture within a system rather than the flow of a message as in a sequence diagram. The message flow between the objects can be represented using a collaboration diagram. Downloaded from Ktunotes.in  Notes on Communication Diagram A collaboration diagram is a collection of named objects and actors along with the links connecting them. They collaborate in performing some task. A collaboration defines a set of participants and relationships that are meaningful for performing some task. Objects collaborate by communicating (passing messages) with one another in order to work together. Objects are able to produce high-level functionalities by working together Collaboration Diagram captures interactions that show the messages passing between objects and their roles within the collaboration Collaboration Diagram emphasizes the structural aspects of an interaction diagram - how lifeline connects. It allows you to focus on the objects rather than focusing on the message flow as described in the sequence diagram. Downloaded from Ktunotes.in  Collaboration Diagram... Its syntax is similar to that of a sequence diagram except that lifeline don't have tails. Each message in a collaboration diagram has a sequence number. Key notations are Objects, Messages and links between the objects. Using tools Sequence diagrams can be easily converted into a collaboration diagram Downloaded from Ktunotes.in  Notations: Objects, Actors, Constraint, Note Objects are model elements that represent instances of a class. Represented with its name and class (underlined in UML 1.x), separated by a colon [ Object_name : class_name ] ○ Multi-object represents a set of lifeline instances. Actors - entity which acts as the invoker of the interaction. ○ Each Actor is named and has a role ○ One actor will be the initiator of the use case Link is a relationship among objects across which messages can be sent. ○ In collaboration diagrams, a link is shown as a solid line between two objects. ○ An object interacts with, or navigates to, other objects through its links to these objects. ○ A link can be an instance of an association, or it can be anonymous, meaning that its association is unspecified. Downloaded from Ktunotes.in  Notations: Messages Messages - A message defines a particular communication between Lifelines/objects of an Interaction In collaboration diagrams, a message is shown as a labeled arrow placed near a link. The message is directed from sender to receiver The association must be navigable in that direction Constraint - A condition or restriction expressed in natural language text. An extension mechanism to refine the semantics of a UML model element. Note - Note contains comments or textual information. Swimlane - A way to group the elements Downloaded from Ktunotes.in Sample collaboration/communication diagrams Downloaded from Ktunotes.in Sample collaboration/communication diagrams Downloaded from Ktunotes.in  Sequence diagram vs Collaboration Diagram Client updating some details in a database - 1. A transaction is started by the client to update the data in DB, 2. Transaction operation writes the values to DB. 3. Once the client is notified with the commit, client destroys the transaction. Downloaded from Ktunotes.in  Drawbacks of a Communication Diagram It can become complex when too many objects are present within the system. It is hard to explore each object inside the system. The state of an object changes momentarily, which makes it difficult to keep track of every single change occurs within an object of a system. Sequence Diagram Communication Diagram Emphasize Time and order of events Messages exchanged between objects Shows participants effectively Good Good Links between participants No notation Explicitly and clearly shows Support asynchronous messages Yes No notation Easy to read message ordering Better Easy to create and maintain Better Downloaded from Ktunotes.in  3. Timing Diagram A timing diagram is a specific behavioral modeling diagram that focuses on timing constraints and state changes to the objects. Timing diagrams are used to explore the behaviors of objects throughout a given period of time. Denotes the transformation of an object from one form into another form. The flow between the software program at various instances of time is represented using a waveform. Downloaded from Ktunotes.in How to draw a Timing Diagram length of a timeline to indicate how long the object remains in a particular state by reading it from left to right. Downloaded from Ktunotes.in  Benefits of Timing Diagram Timing diagrams are used to represent the state of an object at a particular instance of time. It represents the effects of each events(stimuli) in object state transition. Timing diagram allows reverse as well as forward engineering. Timing diagram can be used to keep track of every change inside the system. Very much useful while developing time critical software systems. Drawbacks of a Timing Diagram It is hard to maintain and understand. Available notations are less. Downloaded from Ktunotes.in  4. Interaction overview diagram Interaction overview diagrams focus on the overview of the flow of control where the nodes are interactions (sd) or interaction use (ref). ○ Node type - Interaction - An Interaction diagram of any kind may appear inline as an Activity Invocation. ○ Node type - Interaction Use Large and complex sequence diagrams could be simplified with interaction uses. The other notation elements for interaction overview diagrams are the same as for activity and sequence diagrams. It shows how a set of fragments (portion of interaction) might be initiated in various scenarios Downloaded from Ktunotes.in Interaction Overview Diagram Example - Scheduling System Downloaded from Ktunotes.in  Activity Diagram Another important behavioral diagram in UML to describe the control flow of the system An activity diagram visually presents a series of actions or flow of control in a system Similar to a flowchart or a data flow diagram. It is also called object-oriented flowchart Represents workflows of stepwise activities and actions with support for choice, iteration and concurrency Downloaded from Ktunotes.in Activity Diagram... Demonstrate the logic of an algorithm. Describe the steps performed in a UML use case. Illustrate a business process or workflow between users and the system. Simplify and improve any process by clarifying complicated use cases. Model software architecture elements, such as method, function, and operation Downloaded from Ktunotes.in Basic components of an activity diagram 1. Nodes ○ Action: A single step in the activity wherein the users or software perform a given task. ○ Start node: Symbolizes the beginning of the activity. The start node is represented by a black circle. ○ End node: Represents the final step in the activity. The end node is represented by an outlined black circle. 2. Control flows: Another name for the connectors that show the control flow between steps in the diagram. 3. Partitions (optional) - to organize the nodes in the activity diagram. Downloaded from Ktunotes.in  Notations for Nodes Start symbol - Portrays the beginning of a set of actions or activities. Action symbol - A task to be performed Activity symbol - Indicates the set of actions that make up a modeled process. Includes short descriptions within the shape. Object Node - A node that is used to define object flow in an activity name:type Flow final symbol - Represents the end of a specific process flow. Does not represent the end of all flows in an activity. No effect on parallel flows. End symbol - Stop all control flows and object flows in an activity. Represented by an outlined black circle Downloaded from Ktunotes.in  Notations for control flow Action Flow or Control flow - referred to as paths and edges. They are used to show the transition from one activity state to another. Joint symbol / Synchronization bar - Combines two concurrent activities and re-introduces them to a flow where only one activity occurs at a time. Represented with a thick vertical or horizontal line. Fork symbol - Splits a single activity flow into two concurrent activities. Symbolized with multiple arrowed lines from a join. Loop Node - A structured activity node that represents a loop with setup, test, and body sections Downloaded from Ktunotes.in  Notations... Decision Node - Represents a conditional branch point or decision node. A decision node has one input and two or more outputs. Guards are a statement written next to a decision diamond in [....] Merge Node - Merges the control flows into a single one. The diamond symbol has several inputs and only one output. Accepting an Event (Action) - This action waits for an event to occur. After the event is accepted, the flow that comes from this action is executed. Sending Signals (Action) - Sending a signal means that a signal is being sent to an accepting activity. Downloaded from Ktunotes.in  Notation for grouping - Swimlane Swimlane and Partitions- A way to group activities performed by the same actor on an activity diagram or to group activities in a single thread. Swimlanes are used for grouping related activities in one column/row Swimlanes can be vertical or horizontal, it adds modularity to the diagram. Downloaded from Ktunotes.in Activity diagram syntax Downloaded from Ktunotes.in  Activity diagram - Student enrollment An applicant wants to enroll in the university. The applicant hands a filled out copy of Enrollment Form. The registrar inspects the forms. The registrar determines that the forms have been filled out properly. The registrar informs student to attend in university overview presentation. The registrar helps the student to enroll in seminars The registrar asks the student to pay for the initial tuition. Downloaded from Ktunotes.in Activity diagram - Staff expense submission Downloaded from Ktunotes.in Statechart diagram It is used to capture the dynamic aspects of a system It is also called State Machine or State Transition diagram A state is a conditions or circumstances of an object. ○ Active - performs some activity ○ Inactive - waits for an event It defines different states of an object during its lifetime and these states are getting changed by the events. Statechart diagram describes the transitions from one state to another state in response to some event. Shows discrete behavior of a part of the designed system through finite state transitions. Downloaded from Ktunotes.in Need for Statechart diagram The primary purpose of a state chart diagram is to model interactive systems and define each and every state of an object. To represent the events responsible for change in state (we do not show what processes cause those events). To understand the reaction of objects/classes to internal or external stimuli. Downloaded from Ktunotes.in  Notations for State Machine Initial state - The initial state symbol is used to indicate the beginning of a state machine diagram. Final state - This symbol is used to indicate the end of a state machine diagram. State - a rounded rectangle to represent a state. A state represents the conditions or circumstances of an object of a class at an instant of time. It can be active or inactive. Simple state implies no nested substates. Transition – It is a a solid arrow which represents the path between different states of an object. The arrow is labelled with the event which causes the transition Downloaded from Ktunotes.in  Notations for State Machine Composite state is state that has substates (nested states). UML 2.4 defines composite state as the state which contains one or more regions for substates. Orthogonal state - A composite state with two or more regions is called orthogonal. History states is used to remember the previous state of a state machine when it was interrupted. Downloaded from Ktunotes.in  Notation and Symbol for State Machine Choice pseudostate - contains a condition. Depending upon the result of an evaluated guard condition, a new path is taken for program execution Fork pseudostate vertices serve to split an incoming transition into two or more transitions terminating on orthogonal target vertices. Join pseudostate merges several transitions originating from source vertices in different orthogonal regions Downloaded from Ktunotes.in Statechart diagram example - ATM Downloaded from Ktunotes.in  Eg. University state Diagram The composite state “Enrollment” is made up of various sub states that will lead students through the enrollment process. Once the student has enrolled, they will proceed to “Being taught” and finally to “Final exams.” Downloaded from Ktunotes.in UML Diagrams summary Downloaded from Ktunotes.in Case study : Library Management System Downloaded from Ktunotes.in Case study : Library Management System Downloaded from Ktunotes.in Case study : Library Management System Downloaded from Ktunotes.in Case study : Library Management System Downloaded from Ktunotes.in Case study : Library Management System Downloaded from Ktunotes.in Module 1 - Introduction to Java ► Approaches to Software Design. Functional Oriented Design, Object Oriented Design, Case Study of Automated Fire Alarm System ► Object Modeling Using Unified Modeling Language. Basic Object Oriented concepts, UML diagrams, Use case model, Class diagram, Interaction diagram, Activity diagram, State chart diagram ► Introduction to Java - Java programming Environment and Runtime Environment, Development Platforms - Standard, Enterprise. Java Virtual Machine, Java compiler, Bytecode, Java applet Java Buzzwords, Java program structure, Comments, Garbage Collection, Lexical Issues Downloaded from Ktunotes.in History of Java Java is a general-purpose , Object Oriented Programming language developed by Sun Micro System of USA in 1991. Developed by James Gosling and his team (Green Team) at Sun. First name of Java was “Oak,” later it was renamed “Java” in 1995. Initially designed for small, embedded systems in electronic appliances like set-top boxes. The target of Java is to write a program once and then run this program on multiple operating systems [PLATFORM INDEPENDENCE]. Currently, Java is used in internet programming, mobile devices, games, e-business solutions, etc. Downloaded from Ktunotes.in  Platform dependency issue Platform dependency refers to case where the applications run under only one operating system in one series of computers (platform => OS + H/w). C/C++ executable created for one platform will not run on another, this is nothing but platform dependence. Solution is platform independence which describes a technology to implement things on one platform and use them on another platform without changes Downloaded from Ktunotes.in  Java Compiler Compiler is a software which converts a program written in high level language (Source Language) to low level language (Object/Target/Machine Language) Java compilers include the Java Programming Language Compiler (javac), the GNU Compiler for Java (GCJ), the Eclipse Compiler for Java (ECJ) and Jikes. A Java compiler is a software that takes the java program file(.java) and compiles it to produce a Java class file(.class). The content of class file is not machine code. It contains Java bytecode which can be executed only on Java Virtual Machine (JVM). Syntax: javac HelloWorld.java Downloaded from Ktunotes.in Java Byte Code On compiling java program, we get class file that is nothing but bytecode. Java bytecode is an intermediate representation of the java program which is machine independent. ie, it is not the conventional Machine Code. Byte code cannot directly run on your machine like executable file from C/C++ program, it can run only on Java Virtual Machine. Java bytecode contains the instruction set for the Java Virtual Machine. JVM is responsible to convert bytecode to machine code and execute on your machine. java interpreter is used to execute class file [ java ClassFileName ] Downloaded from Ktunotes.in Platform independence in Java Java compiler output is class file and it is different from machine code. Only machine code can directly execute on your physical machine. Class file contains byte code, which can execute only on Java Virtual Machine(JVM). Java is platform independent because java class files can run on all operating systems without any modifications. If JVM is available for a platform, then Java can run on that platform Downloaded from Ktunotes.in Java Programming Environment Java is a concurrent, class based, object oriented programming and runtime environment, consisting of 1. A programming language (Java) Used by programmers to write the application. 2. An API specification (Java Libraries) Huge number of libraries and components for Java programming 3. A virtual machine specification (JVM) It is a program which provides the runtime environment to execute Java programs Downloaded from Ktunotes.in Java technology: Language specification The Java Language Specification (JLS) defines how a confirming Java application must behave. JLS describes the technical details of how the language is implemented. Java is a high level (human-readable) language which is generally considered easy to read and write. Java is class-based and strictly object-oriented in nature. Java is intended to be easy to learn and to teach. There are many different implementations of JLS available, both proprietary and open source. Fulfils the goal Write Once, Run Anywhere (WORA). ie, the same program can be highly portable and run on many different platforms Downloaded from Ktunotes.in Java technology: Library specification Specifies the standard libraries in Java language. The Java Class Library is a set of standard libraries that is available to any application running on the JVM. This set of libraries is composed of classes that allow programs to handle commons tasks like: network communication, collection manipulation, file operations, user interface creation, etc. Downloaded from Ktunotes.in Java technology: Virtual Machine Specification A virtual machine(VM) is a software implementation of an abstract computer. Java has a VM specification that formally describes what is required in a Java VM implementation. Java Virtual Machine(JVM) is implemented as per Java VM specification to execute the Java bytecode (ie, instruction set understandable to the VM). Most of the JVMs are implemented using C language, JVM developed for one platform will not work on another. ie, JVM is platform dependent. It provides the runtime environment to execute Java programs (bytecode) on a particular platform. Platform independency of Java is due to JVM. Downloaded from Ktunotes.in JVM Architecture JVM is divided into three main subsystems: 1. ClassLoader Subsystem 2. Runtime Data Area 3. Execution Engine Downloaded from Ktunotes.in  JVM - ClassLoader Subsystem ClassLoader subsystem loads, links. and initializes the class file when it refers to a class for the first time at runtime, not compile time. 1.1 Loading - Classes will be loaded by this component. BootStrap ClassLoader, Extension ClassLoader, and Application ClassLoader are the three 1.2 Linking - Performs verification , preparation Verify – Bytecode verifier will verify the generated bytecode Prepare – For all static variables memory will be allocated and assigned with defaults. Resolve – All symbolic memory references are replaced with the original references from Method Area. 1.3 Initialization This is the final phase of ClassLoading; here, all static variables will be assigned with the original values, and the static block will be executed. Downloaded from Ktunotes.in JVM - Runtime Data Area These are storage areas needed during the execution of the program. 1. Method Area – Class-level data will be stored here, including static variables. 2. Heap Area – Objects and their corresponding instance variables and arrays 3. Stack Area – For every thread, a separate runtime stack will be created. For every method call, one entry will be made in the stack memory which is called Stack Frame. a. Local Variable Array – Related to the method, how many local variables are involved and the corresponding values will be stored here. b. Operand stack – acts as runtime workspace to perform operation. c. Frame data – To store all symbols corresponding to the methods. 4. PC Registers – Each thread will have separate PC Registers. 5. Native Method stacks – holds native method information. Downloaded from Ktunotes.in  JVM - Execution Engine The bytecode, which is assigned to the Runtime Data Area, will be executed by the Execution Engine(EE). It reads the bytecode and executes it piece by piece. 1. Interpreter – The interpreter interprets the bytecode faster but executes slowly. 2. JIT Compiler – When EE finds repeated code, it uses the JIT compiler, which compiles the entire bytecode and changes it to native code. This native code will be used directly. a. Intermediate Code Generator – Produces intermediate code b. Code Optimizer – Responsible for optimizing the intermediate code. c. Target Code Generator – Responsible for Generating Native Code d. Profiler – Responsible for finding hotspots in the code. 3. Garbage Collector: Collects and removes unreferenced objects. 4. Java Native Interface (JNI): Interacts with the Native Method Libraries 5. Native Method Libraries: Native Libraries for the EE. Downloaded from Ktunotes.in Java Runtime Environment (JRE) JRE provides the minimum requirements for executing a Java application programs. JRE is an installation package which provides environment to only run(not develop) the java program(or application)onto your machine. JRE can be view as a subset of Java Development Kit. JRE contains Java Virtual Machine (JVM ),core classes, and supporting files JVM is a software implementation of a computer that executes programs like a real machine. Downloaded from Ktunotes.in Java Development Kit (JDK) JDK is a software development environment used for developing and executing Java applications and applets It includes the Java Runtime Environment (JRE), an interpreter/loader (Java), a compiler (javac), an archiver (jar), a documentation generator (Javadoc) and other tools needed in Java development. JDK is only used by Java Developers. Downloaded from Ktunotes.in Development Platforms All Java platforms consist of a Java Virtual Machine (JVM) and an application programming interface (API). Allows applications written for that platform to run on any compatible system with all the advantages of the Java. Major platforms are 1. Java Platform, Standard Edition (Java SE) 2. Java Platform, Enterprise Edition (Java EE) 3. Java Platform Micro Edition (Java ME) Downloaded from Ktunotes.in Java Platform, Standard Edition (Java SE) Java SE lets you develop and deploy Java applications on desktops and personal computers. Latest version is 14. Java SE's API provides the core functionality of the Java programming language. It defines everything from the basic types and objects of the Java programming language to high level classes that are used for networking, security, database access, GUI development, and XML In addition to the core API, the Java SE platform consists of a virtual machine, development tools, deployment technologies, and other class libraries and toolkits commonly used in Java technology applications. Downloaded from Ktunotes.in  Java Platform, Standard Edition (Java SE) For the development of following applications, Java SE is used Standalone Applications for desktop computers. Web supportive applications (Applets) (It is outdated and nobody is using) Database interaction Application (JDBC) Integrated Application (XML) Distributed Application (RMI) Downloaded from Ktunotes.in Java Platform, Enterprise Edition (Java EE) Java EE lets you develop and deploy Java applications on servers and enterprise computers. Java EE provides an API and runtime environment for developing and running large, multi-tiered, reliable, and secure enterprise applications that are portable and scalable and that integrate easily with legacy applications and data. Java Platform, Enterprise Edition (Java EE) is the standard in community-driven enterprise software. Java EE is developed using the Java Community Process(JCP), with contributions from industry experts Enhancements to any Java technology or introduction of new ones occur through Java Specification Requests (JSRs) Java EE platform is built on top of the Java SE platform. Downloaded from Ktunotes.in  Java Platform, Enterprise Edition (Java EE) For the development of following applications Java EE is used Web Application (Servlets/JSPs/JSF) Enterprise Application (EJB) Interoperable Application (Webservices) Downloaded from Ktunotes.in Java Platform, Micro Edition (Java ME) Java ME (Embedded) is designed for resource-constrained embedded devices like wireless modules for M2M, industrial control, smart-grid infrastructure, environmental sensors and tracking, and more. The JME Embedded API is a subset of the Java SE API, along with special class libraries useful for small device application development. Java Card technology provides a secure environment for applications that run on smart cards and other devices with very limited memory and processing capabilities. Downloaded from Ktunotes.in Java FX Java FX technology was a platform for creating rich internet applications written in Java FX Script. Java FX Script is a statically typed declarative language that is compiled to Java technology bytecode , which can then be run on a Java VM. Now it is merged with Java SE Downloaded from Ktunotes.in Java Applet An applet is a Java program that usually runs a in a Web browser. To make interactive web pages with better GUI Downloaded from Ktunotes.in  Java Applet An applet is a special kind of Java program that is designed to be transmitted over the Internet and automatically executed by a Java-compatible web browser. It runs inside the web browser and works at client side Applets are used to make the web pages more dynamic and entertaining Downloaded from Ktunotes.in  Java Applet security aspects. Applets are not stand-alone programs. Instead, they run within a web browser or appletviewer tool. Java applets are loaded on a client when the user visits a page containing an applet. To protecting the user from malicious applets, several restrictions are imposed. Applets are either sandbox applets or privileged applets. Sandbox applets are run in a security sandbox that restricts many operations. An applet cannot load libraries or define native methods. Ordinarily it cannot read or write files on the execution host. It cannot read certain system properties. It cannot make network connections except to the host from where it came from. They cannot run any programs on the local computer. These restrictions are to provide security Downloaded from Ktunotes.in  Applet Life Cycle When an applet is executed within the web browser or in an applet window, it goes through the four stages of its life cycle: New Born, Run, Idle and Destroyed. Applets are sub-classes of java.applet.Applet class Major applet methods. a. init( ) : first method to be called. This is where you should initialize variables. This method is called only once. b. start( ) : called after init( ). It is also called to restart an applet after it has been stopped. c. paint( ) : called each time to redraw the applet window. paint( ) method has one parameter of type Graphics. d. stop( ) : called when a web browser leaves the HTML document containing the applet e. destroy( ) : called when the environment determines that your applet needs to be removed completely from memory. Downloaded from Ktunotes.in Java Applet vs Java Application Downloaded from Ktunotes.in Java Buzzwords Important features of Java language. 1. Simple 2. Object-Oriented 3. Portable 4. Platform independent 5. Secured 6. Robust 7. Architecture neutral 8. Interpreted 9. High Performance 10. Multithreaded 11. Distributed 12. Dynamic Downloaded from Ktunotes.in Java features 1. Simple Java syntax is based on C/C++. If you already understand the basic concepts of object oriented programming, learning Java will be even easier. Java has removed many complicated and rarely-used features, for example, explicit pointers, operator overloading, etc. There is no need to remove unreferenced objects because there is an Automatic Garbage Collection in Java. 2. Object-oriented Java is an object-oriented programming language. OOP means we organize our software as a combination of different types of objects with both data and behavior. Basic concepts of OOPs are: Object, Class, Inheritance Polymorphism, Abstraction, Encapsulation Downloaded from Ktunotes.in  Java features 3. Platform Independent Java is platform independent because java bytecode (class file) can run on any platform, just copy the class file to new platform and run using java interpreter Class file contains the platform independent bytecode which can run on any platform with Java VM. 4. Robust Robustness is the property of being strong and healthy. Java is robust because: 1. There is automatic memory management (garbage collection) in java which runs on the JVM to get rid of objects which are not being used anymore. 2. There is a lack of explicit pointers that avoids security problems. 3. There are exception handling and the type checking mechanism. 5. Interpreted Java programs are compiled into an intermediate representation called Java bytecode. The byte code is interpreted to any machine code so that it runs on the native machine. Downloaded from Ktunotes.in  Java features 6. Secured Java is secure, we can develop virus-free systems. It is secured because, No explicit pointer, Java Programs run inside a virtual machine sandbox JVM has Classloader to load Java classes dynamically. It adds security by separating the package for the classes of the local file system from those that are imported from network. Bytecode Verifier checks the code fragments for illegal code that can violate access right to objects. Security Manager determines what resources a class can access. Java language provides these securities by default. Some security can also be provided by an application developer explicitly through SSL, JAAS, Cryptography, etc. Downloaded from Ktunotes.in  Java features 7. Architecture-neutral Java is architecture neutral because there are no implementation dependent features, for example, the size of primitive types is fixed. In C programming, int data type occupies 2 bytes of memory for 32-bit architecture and 4 bytes of memory for 64-bit architecture. However, it occupies 4 bytes of memory for both 32 and 64-bit architectures in Java. 8. Portable Java is portable because it facilitates you to carry the Java bytecode to any platform. It doesn't require any implementation. 9. High-performance Java is faster than other traditional interpreted programming languages because Java bytecode is "close" to native code. It is still a little bit slower than a compiled language (e.g., C++). Downloaded from Ktunotes.in  Java features 10. Distributed Java is distributed because it facilitates users to create distributed applications in Java. RMI and EJB are used for creating distributed applications. This feature of Java makes us able to access files by calling the methods from any machine on the internet. 11. Multi-threaded A thread (light weight process) is a single sequential flow of control within a program. Java supports multiple concurrent threads with APIs to manage the thread states. We can write Java programs that deal with many tasks at once by defining multiple threads. 12. Dynamic Java supports dynamic loading of classes. It means classes are loaded on demand at run time. Java supports dynamic compilation and automatic memory management (garbage collection) at JVM level. Downloaded from Ktunotes.in Garbage Collection Memory leak is a type of resource leak that occurs when computer programs fails to release the allocated memory after use. This is a common issue in C/C++ programs. Java’s answer to this issue is Automatic Garbage Collection When JVM starts up, it creates a heap area which is known as runtime data area. This is where all the objects (instances of class) are stored The process of removing unused objects from heap memory is known as Garbage collection and this is a part of memory management in Java. In java, garbage means unreferenced objects. In Java responsibility of releasing unused memory is with JVM. In C/C++.. Programmer is responsible for memory release and it is the major reason for memory leaks and program crashes. Downloaded from Ktunotes.in Garbage Collection In java, garbage means unreferenced objects. Main objective of Garbage Collector is to free heap memory by destroying unreachable objects. Unreachable objects : An object is said to be unreachable when there is no valid references to that object exist. Eligibility for garbage collection : object must be unreachable. finalize() method – This method is invoked each time before the object is garbage collected and it is intended to perform cleanup processing. Garbage collector releases only those objects that are created by new keyword. So if we have created any object without new, we can use finalize method to perform cleanup processing Downloaded from Ktunotes.in Request for Garbage Collection We can request to JVM for garbage collection however, it is upto the JVM when to start the garbage collector. gc() method is used to call garbage collector explicitly. It only request the JVM for garbage collection. However gc() method does not guarantee that JVM will perform the garbage collection. This method is present in System and Runtime class, functionally both are same. Downloaded from Ktunotes.in Comments Downloaded from Ktunotes.in Comments... Downloaded from Ktunotes.in Java program structure Downloaded from Ktunotes.in  Java program structure Document section (optional) Add comments describing the details of author, purpose, licence, etc Package Statement (optional) You can create a package with any name to organize the classes of that file. A package is to group classes that are defined by a name. It is like a folder in which all the classes present in that file are kept. It is declared as: package package_name; Downloaded from Ktunotes.in  Java program structure Import Statement (optional) This line indicates that if you want to use a class of another package, then you can do this by importing it directly into your program. E.g. import java.io.*; // importing all the classes from java.io package Interface statement (optional) Interfaces are like a class that includes a group of method declarations. It's an optional section and can be used when programmers want to implement multiple inheritances within a program. Class Definition (optional) A Java program file may contain several class definitions. But only one public class is allowed in a file File name and the public class name should be same. Downloaded from Ktunotes.in  Java program structure Main Method Class Every Java stand alone program requires the main method as the starting point of the program. There may be many classes in a Java program, but only one class defines the main method. public static void main(String args[]) It is declared public , it means that it can also be used by code outside of its class. static indicates classified scope, ie we want to access a method without creating its object, as we call the main method, before creating any class objects. void indicates that a method does not return a value. main is a method; this is a starting point of a Java program. String args[] - method receives an array of strings, it is used to receive the command line arguments to your program. Downloaded from Ktunotes.in  Sample Program Downloaded from Ktunotes.in Downloaded from Ktunotes.in Java Lexical Issues or Java Lexeme or Java Tokens Tokens are the smallest individual building block or smallest unit of a program. Java compiler uses it for constructing expressions and statements. Java program is a collection of different types of tokens, comments, and white spaces. Downloaded from Ktunotes.in  Tokens - Keywords A keyword is a reserved word. In Java there are 50 keywords. The meaning of the keywords has already been described to the java compiler. These meaning cannot be changed. Thus, the keywords cannot be used as variable names because that would try to change the existing meaning of the keyword, which is not allowed. Downloaded from Ktunotes.in  Tokens - Identifiers Identifiers are the names of variables, methods, classes, packages and interfaces Allowed characters for identifiers are all alphanumeric characters([A-Z],[a-z],[0-9]), ‘$‘(dollar sign) and ‘_‘ (underscore). All identifiers must start with either a letter( a to z or A to Z ) or currency character($) or an underscore. They must not begin with a digit After the first character, an identifier can have any combination of allowed characters. Identifiers in Java are case sensitive, foo and Foo are different. A Java keywords cannot be used as an identifier. They can be any length Eg: int a; , char name; Downloaded from Ktunotes.in  Tokens - Constants or Literals Constants are fixed values of a particular type of data, which cannot be modified in a program. Java language specifies five major type of literals. In Java, a character preceded by a backslash (\) is an escape sequence and has special meaning. Downloaded from Ktunotes.in  Tokens - Separators There are few symbols in java that are used as separators. A separator is a sequence of one or more characters used to specify the boundary between separate, independent regions in plain text or other data stream. The most commonly used separator in java is the semicolon ' ; '. Downloaded from Ktunotes.in  Tokens - Operators An operator is a symbol that takes one or more arguments and operates on them to produce a result. 1. Unary Operator 2. Arithmetic Operator 3. Shift Operator 4. Relational Operator 5. Bitwise Operator 6. Logical Operator 7. Ternary Operator 8. Assignment Operator Downloaded from Ktunotes.in  Tokens - Comments & White space White space Java is a free-form language. This means that you do not need to follow any special indentation rules White space in Java is used to separate tokens in the source file. It is also used to improve readability of the source code. Eg: int i = 0; White spaces are required in some places. For example between the int keyword and the variable name. In java whitespace is a space, tab, or newline Comments Java supports 3 types of comments. Downloaded from Ktunotes.in References Rajib Mall, Fundamentals of Software Engineering, 4th edition, PHI, 2014. UML Diagrams - www.uml-diagrams.org Visual Paradigm - www.visual-paradigm.com GeeksforGeeks - www.geeksforgeeks.org Wikipedia - www.wikipedia.org Tutorialspoint - www.tutorialspoint.com Java Zone - https://dzone.com Disclaimer - This document contains images/texts from various internet sources. Copyright belongs to the respective content creators. Document is compiled exclusively for study purpose and shall not be used for commercial purpose. Downloaded from Ktunotes.in