Object Lifecycle and State Changes in Java

Chapter 1: Basic Principles: Which Object for Computer Science?

• This chapter introduces basic principles of computer science, focusing on Object-Oriented Programming (OOP).
• Software uses data, requiring understanding, analysis, updating, and storage.
• OOP is a method for managing this data efficiently.
• OOP organizes data and actions in an understandable way.
• Data classes and objects allow for logical and easy-to-follow data management.

Introduction

• Software works with data; effectively using data requires understanding, analysis, updating, and storage.
• How can all this data be managed effectively?
• Object-Oriented Programming (OOP) provides a structured approach to manage data in a clear and understandable way.
• OOP organizes data and actions into a clear structure (classes).
• Once defined classes and objects are set up, data can be worked with in an organized and logical way.

Introduction (2)

• Perception of the environment involves noticing specific objects (like cars, trees).
• Cognitive mechanisms highlight the selective way we perceive things to understand object-oriented programming.
• Selective attention is the process of focusing on certain aspects while ignoring others (like air, temperature).
• Objects have attributes (like shape, color, dimensions).
• Perceptual segmentation lets us differentiate objects according to their attributes.

The trio <entity, attribute, value>

• The world is described using entities, attributes, and values.
• An entity is anything identifiable (e.g., a car, a person, a company).
• Attributes are properties that define an entity (color, age, size).
• Values are the specific attributes' definitions (red, 4 years old, large).
• Attributes define and detail objects.
• Common attributes can be applied to many different objects.
• Classification is the grouping of objects into categories.

An Example of the trio <entity, attribute, value>

• Shows a diagram of an example (like a student).
• Values are shown for attributes like age and address.
• Each attribute is connected to an entity.

What is Object Oriented Programming?

• OOP is a coding method focused on 'objects' instead of functions and procedures.
• OOP simplifies software development and helps model any data.
• Classes define data and provide reusable blueprints for creating objects.
• OOP facilitates intuitive modeling and reduces software complexity, development time, and maintenance.

What is an Object

• An object combines both data (state) and behavior (methods).
• State represents the data of an object (e.g., color, brand, speed of a car).
• Methods define the actions an object can perform (e.g., accelerate, brake, honk).
• Identity distinguishes each object uniquely.

Storage of Objects in Memory

• Each object in a program is allocated a memory space.
• Primitive data types (integers, floats, characters) have fixed sizes.
• Object attributes are stored using primitive data types for efficiency.
• The system determines the memory space needed to store an object.

Example of object memory size calculation

• Shows calculation of memory required to store an object.
• Example attributes are considered (like age, height, gender, name).
• Calculates the memory size for these attributes using appropriate sizes for primitive data types.

The Referent of an Object

• Objects have unique names to identify them.
• Names correspond to objects' memory addresses.
• Memory addresses ensure that no two objects occupy the same memory space.
• A referent (a special variable) stores the memory address of an object.
• Memory space is dedicated to storing object references symbolically.
• Memory addresses are typically 32-bit values.
• A referent is a 32-bit variable holding the object's memory address, facilitating efficient memory access.

The Referent of an Object (2)

• Stack memory holds temporary method data.
• Heap memory stores objects; Java cleans up unused objects automatically.

Stack memory example

• Illustrates how local variables are stored in stack memory during method calls and are removed after execution.

Heap memory example

• Shows how objects are stored in heap memory and persist until they are no longer needed, managed by Java's Garbage Collector.

Indirect Addressing

• Multiple referents are possible for a single object (using different names).
• Different names reference the same object in different parts of the program.
• Indirect addressing enables multiple references to the same object, promoting modular programming.
• Avoiding unnecessary duplication improves memory efficiency.

Multiple Referents Example

• Illustrates an example, where multiple references point to the same object in memory, showing that modifying one reference also affects others.

The Object in Its Passive Version

• Objects are usually thought of as wholes.
• Objects are composed of parts (sub-objects).
• OOP distinguishes an object's public interface (how other objects interact) from its internal functioning.
• Separation between external and internal object properties is important for code organization and modularity.

Object Composition

• Composition creates complex objects by combining simpler ones.
• Component objects depend on existence of the composite object.
• Real-world examples (like houses and rooms) demonstrate object composition.
• Composition simplifies complex systems by structuring them from simpler parts using dependency relationships.

Dependence Relationship

• Objects can be connected without being fully dependent.
• Dependencies explain how objects connect/manage, as an example, passengers and a car.
• Objects can interact (use methods on each other), but don't have a strict containment relationship.
• Flexible and realistic modeling is achieved through this process.
• Libraries (books, and authors) exemplify an association.

The object in its active version

• Objects can move, change, and react to events in programs.
• Objects respond to signals, interact with others, and change state, highlighting their dynamic nature.
• Activities modify the object's attributes and behaviors.

Object State

• Object state is the object's current condition using its attributes.
• Attributes define the characteristics describing an object (e.g., color, speed).
• Changes to attributes don't change underlying object identity.
• Memory operation to update attributes doesn't alter the object's address.
• An object persists until deletion from memory.
• Objects' time in memory reflects a lifecycle.

Object Lifecycle

• An object's life cycle involves creation, use, modification, and destruction.
• Objects begin with state initialization.
• Objects react to internal and external program changes.
• Objects persist until deletion or unneeded, freeing memory.

Responsibility

• Object state changes result from object methods.
• Operations drive state changes, like a traffic signal changing colors.
• Methods/Operations change an attribute value based on predefined rules or conditions.

Exercise

• Composition influences memory management by deleting related objects to release memory.
• Objects within a composite object are destroyed when the main object is destroyed.
• This ensures memory is well-managed; related objects do not persist.

QCM (Question with Multiple Choices)

• Several questions assessing understanding of OOP concepts.

QCM (2)

• Further QCM questions checking understanding of OOP concepts.

QCM (3)

• More QCM assessing understanding of object-oriented programming.

Introduction to the concept of a Class

• A class is a blueprint for objects with specific data and methods.
• Instances of a class are created from the blueprint (objects).
• Instance variables hold the data of an object.

Introduction to the concept of a Class (2)

• Shows a basic Java class.
• Shows how an instance variable is declared and used.

Class Constructor

• Constructors are special methods, having same name as class, initializing object attributes when created.
• The this keyword refers to the current object, accessing and working with instance variables and methods.

Getter

• A getter method retrieves an object's attribute value.
• It follows standard OOP practice of using get followed by attribute name.

Setter

• A setter method sets or updates an object's attribute value.
• Setter methods use set followed by attribute name.

Object instance

• Creating an object of a class is an object instance.
• Using the new keyword creates an instance of a class.

Example of Object instance

• Shows a Java example with object instantiation, setting values, and manipulating object attributes and methods.

Instance variables and class variables

• Instance variables belong to specific objects; each object has its own copy.
• Class variables belong to the class itself; all objects share a single copy.

Instance variables and class variables (2)

• Example code snippet illustrating instance variables and their declaration, along with constructor methods.

Instance variables and class variables (3)

• Static class variables are associated with the class rather than instances, accessible using the class name.
• Only one copy exists for all objects; it's initialized when the class is loaded.

Instance variables and class variables (4)

• Detailed example of class variables in Java; demonstrates the incrementing class variable with each object.

QCM

• Various multiple choice questions about Java constructors, the this keyword, scope, and instance and class variables.

QCM (2)

• Additional multiple choice questions about getters, setters, and static variables.

QCM (3)

• More multiple choice questions about the differences between instance and class variables.

Object-Oriented Programming (OOP) Languages vs. Languages Manipulating Objects

• OOP languages let programmers define their own classes.
• OOP enables creation of new classes, defining methods, and specifying object attributes.
• OOP is used to create and manage objects to perform complex tasks.
• Languages manipulating objects typically only use predefined classes, like libraries.

Executing the Method on a Specific Object

• Methods operate on a specific object using the dot (.) operator.
• The dot notation connects a method with the object. Methods have access to the object's attributes.

Executing the Method on a Specific Object (2)

• Methods, like turnOn(), need to know which object they're operating on.
• The dot notation connects a method with a specific object to ensure it modifies the correct data, attributes.

How Objects Communicate

• Objects interact to perform tasks through messages and methods.
• The interaction between objects, where one object triggers an action in another is essential for OOP program functionality.

Finding Message Recipients

• Objects need to identify the targeted object. A system determines if the message is for the correct object before continuing.
• Passing data and referencing can keep objects updated. This reduces repetitive communication and makes processing simpler.

Example: Finding Message Recipients (2)

• Detailed examples of car and parking classes, which reference each other and communicate about presence, position, and parking related issues.

What is Inheritance

• A fundamental concept in OOP.
• A new class (subclass) inherits from an existing class (superclass).
• This promotes code reuse and a hierarchical organization of classes.

Hierarchy of Objects

• Objects can be grouped in a hierarchy from general (parent) to specific (child) classes.
• Examples like 'phone,' 'iPhone', or 'flip phone', show organization.
• Inheritance organizes classes into hierarchies.

Contextual Dependence on the Right Taxonomic Level

• Specific terms are useful in certain contexts.
• General terms may be insufficient in contexts requiring more detail.
• Terms like "means of transportation" are broader and less precise than 'car'.

Contextual Dependence on the Right Taxonomic Level (2)

• Different levels of detail can be helpful in specific contexts to ensure efficient communication.
• Specificity in language clarifies meaning and avoids ambiguity.

Polymorphism

• Polymorphism enables different objects to respond differently to the same message.
• Method or reference variable behaviors vary for different class types.
• Polymorphism enhances inheritance by adding flexibility to objects behavior.

Polymorphism Example

• A mouse click on the computer screen can result in multiple outcomes for different objects depending on what's being clicked on.
• A single action has different specific effects on various objects.

References

• Various cited works about object-oriented programming provide references to learning materials.

This quiz explores the concepts of object lifecycle, state changes, and memory management in Java programming. It covers key topics such as object identity, operations affecting state, and memory allocation. Test your knowledge of how objects behave throughout their lifecycle in Java.