Java Programming: Features, JVM, and Core Concepts

• Study notes on Java Programming, covering features, JVM, data types, OOP concepts, I/O, arrays, strings, and more.

Core Java Features

• Platform independence, achieved by running on the Java Virtual Machine (JVM).
• Supports object-oriented programming (OOP).
• Designed with automatic memory management.

Java Virtual Machine (JVM)

• Creates a platform-independent environment for executing Java bytecode.
• Acts as a runtime engine that interprets Java bytecode.

Parts of Java

• Java Development Kit (JDK): Provides tools needed to develop and run Java programs.
• Java Runtime Environment (JRE): Provides the environment to run compiled Java programs.
• Java Virtual Machine (JVM): Executes the bytecode.

Steps to Java Programming

• Write the Java code.
• Compile the code using a Java compiler (javac).
• Execute the compiled code using the Java Runtime Environment (java).

API Documentation

• The Java API documentation provides information about the classes and interfaces in the Java standard library.
• Essential for understanding how to use predefined classes and methods.

Starting Java Programming

• Create the first program using public static void main(String[] args).
• Use System.out.println() to display output.

Importing Classes

• The import statement allows using classes from other packages.
• Example: import java.util.Scanner; to use the Scanner class.

Formatting the Output

• Use System.out.printf() or String.format() for formatted output.
• Format specifiers like %d, %f, and %s are used for integers, floats, and strings, respectively.

Naming Conventions

• Class names start with an uppercase letter (e.g., MyClass).
• Method and variable names start with a lowercase letter (e.g., myMethod).
• Constants are in uppercase (e.g., MAX_VALUE).

Data Types in Java

• Primitive data types: byte, short, int, long, float, double, boolean, char.
• Non-primitive data types: Classes, interfaces, arrays, and strings.

Operators in Java

• Arithmetic operators: +, -, *, /, %.
• Relational operators: ==, !=, >, <, >=, <=.
• Logical operators: &&, ||, !.
• Assignment operators: =, +=, -=, *=, /=, %=.

Control Statements

• Conditional statements: if, else, else if.
• Looping statements: for, while, do-while.

Switch Statement

• Allows multi-way branching based on the value of a variable.
• switch(variable) { case value1: ... break; case value2: ... break; default: ... }

Break Statement

• Terminates the current loop or switch statement.
• Transfers control to the next statement after the loop or switch.

Continue Statement

• Skips the rest of the current iteration of a loop.
• Continues with the next iteration of the loop.

Return Statement

• Exits from the current method.
• Can return a value from the method.

Input/Output in Java

• Accepting input from the keyboard using Scanner.
• Displaying output using System.out.print() and System.out.println().
• Formatting output using System.out.printf().

Arrays

• Definition: A collection of elements of the same data type.
• Types: Single-dimensional, multi-dimensional, and jagged arrays.
• Access elements using index (e.g., array[0]).

Single-Dimensional Arrays

• Declared as int[] arr = new int[5];.
• Elements are accessed using an index from 0 to length - 1.

Multi-Dimensional Arrays

• Arrays of arrays (e.g., int[][] matrix = new int[3][3];).
• Useful for representing matrices or tables.

Jagged Arrays

• Arrays where each row can have a different number of columns.
• Example: int[][] jagged = new int[3][]; jagged[0] = new int[1]; jagged[1] = new int[2]; jagged[2] = new int[3];.

Array Length Property

• array.length returns the number of elements in the array.
• Useful for iterating through the array.

Array by Command Line Argument

• Passing arguments to the main method when running the program.
• Arguments are passed as strings (e.g., java MyClass arg1 arg2).

String

• Creating: String str = "Hello"; or String str = new String("Hello");.
• Immutable: Once created, the value of a string cannot be changed.

String Class Methods

• length(): Returns the length of the string.
• charAt(int index): Returns the character at the specified index.
• substring(int beginIndex, int endIndex): Returns a substring.
• concat(String str): Concatenates two strings.
• equals(Object obj): Compares two strings for equality.
• equalsIgnoreCase(String str): Compares two strings ignoring case.

String Comparison

• Using equals() to compare the content of strings.
• Using == to compare the references of strings (checks if they point to the same object).

Immutability of String

• String objects are immutable, meaning their state cannot be modified after creation.
• When a string is modified, a new string object is created.

StringBuffer and StringBuilder

• Mutable: Can be modified after creation.
• Used when frequent modifications to strings are needed.

Creating StringBuffer Objects

• StringBuffer sb = new StringBuffer("Hello");.
• Initial capacity is 16 characters if no initial string is provided.

StringBuffer Class Methods

• append(String str): Appends the specified string to this character sequence.
• insert(int offset, String str): Inserts the string into this character sequence.
• replace(int start, int end, String str): Replaces characters within a substring with the specified string.
• delete(int start, int end): Deletes characters within a substring.
• reverse(): Reverses the order of characters in this sequence.

StringBuilder Class

• Similar to StringBuffer, but not synchronized (faster).
• Use when thread safety is not a concern.

StringBuilder Class Methods

• Same methods as StringBuffer (e.g., append(), insert(), replace(), delete(), reverse()).

String vs StringBuffer

• String is immutable; StringBuffer is mutable.
• String is suitable for simple string operations; StringBuffer for frequent modifications.

StringBuffer vs StringBuilder

• StringBuffer is synchronized (thread-safe); StringBuilder is not (faster).
• Use StringBuffer in multi-threaded environments; StringBuilder in single-threaded environments.

OOPs Concepts

• Introduction to OOP’s: Object-oriented programming paradigm.
• Features of OOP’s: Encapsulation, inheritance, polymorphism, abstraction.

Features of OOP’s

• Encapsulation: Bundling data and methods that operate on the data within a class.
• Inheritance: Deriving new classes from existing classes.
• Polymorphism: Ability of an object to take on many forms.
• Abstraction: Hiding complex implementation details and showing only essential features.

Access Specifiers

• Public: Accessible from anywhere.
• Private: Accessible only within the class.
• Protected: Accessible within the class, subclasses, and within the same package.
• Default (no specifier): Accessible within the same package.

Constructor

• A special method used to initialize objects.
• Has the same name as the class.
• Can be overloaded (multiple constructors with different parameters).

Class and Object

• Class: A blueprint for creating objects.
• Object: An instance of a class.
• Object creation: MyClass obj = new MyClass();.

Initializing Instance Variables

• Using constructors or direct assignment.
• Example: MyClass obj = new MyClass("Hello"); or obj.name = "Hello";.

Methods

• Instance method: Operates on an instance of the class.
• Static method: Belongs to the class and can be called without creating an instance.
• this keyword: Refers to the current instance of the class.

Instance Method

• Accessed using an object of the class (e.g., obj.myMethod();).
• Can access instance variables of the class.

Static Method

• Accessed using the class name (e.g., MyClass.myMethod();).
• Cannot access instance variables directly.

'this' Keyword

• Refers to the current instance of the class.
• Used to differentiate between instance variables and method parameters with the same name.

Passing Primitive Data Types to Method

• Passed by value (a copy of the value is passed).
• Changes made to the parameter inside the method do not affect the original variable.

Passing Objects to Method

• Passed by reference (a copy of the reference is passed).
• Changes made to the object’s state inside the method affect the original object.

Passing Arrays to Method

• Arrays are objects, so they are passed by reference.
• Changes made to the array elements inside the method affect the original array.

Recursion

• A method calling itself.
• Requires a base case to stop the recursion.

Inheritance

• Inheritance introduction: A class inherits properties and methods from another class.
• Use of inheritance: Code reuse, creating a hierarchy of classes.
• Types of inheritance: Single, multi-level, hierarchical.

Types of Inheritance

• Single: A class inherits from one superclass.
• Multi-level: A class inherits from a subclass, which in turn inherits from another class.
• Hierarchical: Multiple classes inherit from one superclass.

'super' Keyword

• Refers to the superclass of the current class.
• Used to call superclass constructors and methods.

Use of Protected Access Specifier

• Accessible within the class, subclasses, and within the same package.
• Provides more encapsulation than default access.

Polymorphism

• Polymorphism introduction: Ability of an object to take on many forms.
• Static and dynamic Polymorphism.

Static Polymorphism (Compile-Time)

• Achieved through method overloading and operator overloading.
• Resolved at compile time.

Dynamic Polymorphism (Runtime)

• Achieved through method overriding.
• Resolved at runtime.

Method Overriding

• A subclass provides a specific implementation of a method that is already defined in its superclass.
• Method signature must be the same.

Method Overload vs Method Overriding

• Overloading: Multiple methods with the same name but different parameters.
• Overriding: A subclass provides a specific implementation of a method already defined in its superclass.

Use of 'final' Keyword

• A final variable cannot be changed.
• A final method cannot be overridden.
• A final class cannot be subclassed.

Abstract Method and Class

• Abstract method: A method without an implementation (declared using the abstract keyword).
• Abstract class: A class that contains abstract methods or is declared abstract.
• Abstract classes cannot be instantiated.

Interface

• Interface introduction: A contract that defines a set of methods that a class must implement.
• Multiple inheritance using interfaces.

Multiple Inheritance Using Interfaces

• A class can implement multiple interfaces.
• Achieves multiple inheritance of type, but not implementation.

Abstract Class vs Interfaces

• Abstract class can have both abstract and concrete methods; interface only has abstract methods (or default/static methods).
• A class can extend only one abstract class, but implement multiple interfaces.

Packages

• Introduction to package: A way to organize classes and interfaces into namespaces.
• Types of packages: Built-in and user-defined package.

Types of Packages

• Built-in packages: Included in the Java API (e.g., java.util, java.io).
• User-defined packages: Created by developers to organize their classes.

Creating and Importing Package

• Creating: Use the package keyword at the beginning of the file.
• Importing: Use the import statement to use classes from other packages.

Relating Sub Package in Package

• Subpackages are packages within a package (e.g., java.util.concurrent).
• To use a class from a subpackage, specify the full package name (e.g., java.util.concurrent.ExecutorService).

Interfaces in Package

• Interfaces can be included in packages.
• Follow the same rules for creating and importing packages.

Access Specifier in Package

• Public classes and interfaces are accessible outside the package.
• Default (package-private) classes and interfaces are only accessible within the same package.

Use Math Package

• The java.lang.Math package provides methods for performing mathematical operations (e.g., Math.sqrt(), Math.sin(), Math.cos()).
• No need to import java.lang.Math as it is automatically included.

Java I/O and Stream

• Java streams: Sequence of data flowing from a source to a destination.
• OutputStream vs InputStream: OutputStream for writing data; InputStream for reading data.

OutputStream Class

• Abstract class for writing bytes to an output destination.
• Subclasses include FileOutputStream, ByteArrayOutputStream, ObjectOutputStream.

InputStream Class

• Abstract class for reading bytes from an input source.
• Subclasses include FileInputStream, ByteArrayInputStream, ObjectInputStream.

Hierarchy of OutputStream and InputStream Class

• OutputStream (abstract) -> FileOutputStream, ByteArrayOutputStream, ObjectOutputStream
• InputStream (abstract) -> FileInputStream, ByteArrayInputStream, ObjectInputStream

FileWriter Class

• Writes characters to a file.
• Suitable for writing text data.

FileReader Class

• Reads characters from a file.
• Suitable for reading text data.

File Class Methods

• createNewFile(): Creates a new file.
• exists(): Checks if a file exists.
• getName(): Returns the name of the file.
• length(): Returns the length of the file in bytes.
• delete(): Deletes the file.

Creating File

• File file = new File("myfile.txt"); file.createNewFile();.

Reading File

• Using FileReader or FileInputStream to read data from a file.
• Use BufferedReader for efficient reading of text files.

File Copy

• Reading data from one file and writing it to another file.
• Using FileInputStream and FileOutputStream for binary files.
• Using FileReader and FileWriter for text files.

Serialization and De-Serialization in File

• Serialization: Converting an object to a stream of bytes for storage.
• De-serialization: Converting a stream of bytes back into an object.
• Use ObjectOutputStream for serialization and ObjectInputStream for de-serialization.

Exception Handling

• Exception Handling: Mechanism to handle runtime errors.
• Exception Handling classes Java Exceptions.

Java Exceptions

• Throwable (base class) -> Exception (checked and unchecked), Error (unrecoverable).
• Checked exceptions: Must be caught or declared (e.g., IOException, SQLException).
• Unchecked exceptions: Errors that occur at runtime, can be avoided via coding (e.g., NullPointerException, ArrayIndexOutOfBoundsException).

Try-Catch Block

• Used to catch exceptions.
• try { ... } catch (ExceptionType e) { ... }.

Multiple Catch Block

• Catching multiple exceptions.
• try { ... } catch (ExceptionType1 e1) { ... } catch (ExceptionType2 e2) { ... }.

Nested Try

• A try block inside another try block.
• Useful for handling different types of exceptions at different levels.

Finally Block

• Always executed, whether an exception is thrown or not.
• Used for cleanup operations (e.g., closing resources).

Throw Keyword

• Used to explicitly throw an exception.
• throw new ExceptionType("message");.

Throws Keyword

• Used in method declaration to indicate that the method might throw an exception.
• public void myMethod() throws ExceptionType { ... }.

Throw vs Throws

• throw is used to throw an exception; throws is used to declare an exception.
• throw is used within a method; throws is used in the method signature.

Final vs Finally

• final is a keyword used to declare constants, prevent method overriding, and prevent class inheritance.
• finally is a block that is always executed after a try block, regardless of whether an exception is thrown.

Custom Exceptions

• Creating user-defined exception classes by extending the Exception class.
• Useful for handling specific error conditions in an application.

Collection Framework

• Typecasting: Converting a variable from one data type to another.
• Types of typecasting.

Types of Typecasting

• Primitive type conversion: Implicit (widening) and explicit (narrowing).
• Object type conversion: Upcasting and downcasting.

Wrapper Classes

• Use of Wrapper classes: Provides a way to use primitive data types as objects.
• Number classes (Long, Integer, Byte, Short, Float, and double) and importance methods of Number class.

Number Classes

• Integer, Double, Float, Long, Short, Byte.
• Provide methods for converting between primitive types and objects (e.g., intValue(), doubleValue(), parseFloat(), parseLong()).

Character Class

• Represents a single character as an object.
• Important methods of character class.

Important Methods of Character Class

• isLetter(), isDigit(), isWhitespace(), toUpperCase(), toLowerCase().

Autoboxing and Unboxing

• Autoboxing: Automatic conversion of primitive types to their corresponding wrapper classes.
• Unboxing: Automatic conversion of wrapper class objects to their corresponding primitive types.

Collection Framework

• Use of Collection framework: Provides a set of interfaces and classes for storing and manipulating groups of objects.
• Hierarchy of Collection Framework.
• Collection objets-Set, List, Map, Queue
• Collection classes-Stack, ArrayList, vector, LinkedList, priority queue, HashSet, LinkedHashSet, SotredSet, TreeSet, Hashtable and HashMap

Hierarchy of Collection Framework

• Collection (interface) -> List, Set, Queue (interfaces).
• Map (interface).

Collection Objects

• Set: Unordered collection of unique elements (e.g., HashSet, TreeSet).
• List: Ordered collection of elements (e.g., ArrayList, LinkedList).
• Map: Collection of key-value pairs (e.g., HashMap, TreeMap).
• Queue: Collection for holding elements prior to processing.

Collection Classes

• Stack: LIFO (Last-In-First-Out) data structure.
• ArrayList: Dynamically resizable array.
• Vector: Similar to `ArrayList, but synchronized.
• LinkedList: Doubly-linked list.
• PriorityQueue: Queue that processes elements based on priority.
• HashSet: Unordered set implemented using a hash table.
• LinkedHashSet: Ordered set implemented using a hash table and a linked list.
• TreeSet: Sorted set implemented using a tree.
• Hashtable: Hash table implementation of the Map interface (synchronized).
• HashMap: Hash table implementation of the Map interface (not synchronized).

Multithreading

• Singletasking: Executing one task at a time.
• Multi-tasking: Executing multiple tasks concurrently.
• Use of thread: Allows concurrent execution of tasks.

Creating and Running Thread

• Extending the Thread class or implementing the Runnable interface.
• Starting a thread using the start() method.

Terminating Thread

• Using the interrupt() method to interrupt a thread.
• Thread can terminate itself by completing its run() method.

Thread Class Methods

• start(): Starts the thread.
• run(): Contains the code to be executed by the thread.
• sleep(): Causes the thread to sleep for a specified time.
• join(): Waits for the thread to die.
• interrupt(): Interrupts the thread.

Multiple Threading

• Creating multiple threads to execute tasks concurrently.
• Requires synchronization to avoid race conditions.

Thread Communication

• Using wait(), notify(), and notifyAll() methods for inter-thread communication.
• Requires synchronized blocks or methods.

Thread Priorities

• Assigning priorities to threads to influence their scheduling.
• Priorities range from 1 (lowest) to 10 (highest).

Application of Thread and Thread Lifecycle

• Thread Lifecycle: New, Runnable, Running, Blocked/Waiting, Terminated.
• Applications: Concurrent execution of tasks, improving application responsiveness.

Networking

• Introduction to Networking: Connecting devices to share resources.
• TCP/IP protocol, UPD protocol, socketprogramming, InetAdressClass, URLConnectionclass, communicationbetweenclientandserver,twowaycommunicationbetweenclientandserver.

TCP/IP Protocol

• Transmission Control Protocol/Internet Protocol.
• Provides reliable, ordered, and error-checked delivery of data.

UDP Protocol

• User Datagram Protocol.
• Provides connectionless, unreliable delivery of data.
• Faster than TCP/IP.

Socket Programming

• Using sockets to establish a connection between two devices.
• Server socket listens for incoming connections; client socket connects to the server.

InetAddress Class

• Represents an IP address.
• Used to get the IP address of a host.

URLConnection Class

• Represents a connection to a URL.
• Used to read data from a URL.

Communication Between Client and Server

• Establishing a socket connection.
• Sending and receiving data using input and output streams.

Two Way Communication Between Client and Server

• Both client and server can send and receive data.
• Requires handling input and output streams in both client and server.

Swing

• Hierarchy of Swing classes JButton,JLabelJava,JTextField, JTextArea,JPasswordField,JCheckBox,JRadioButton,JComboBox, ,JList, JOptionPaneJavaJScrollBar,JMenuItem&JMenuJava, Image Eventhadling:-JavaEventHandling,JavaEventclassesandListener interfaces. LayoutManager-BorderLayoutFlowLayout,GridLayout,CardLayout, BoxLayout

Hierarchy of Swing Classes

• JButton: A push button component.
• JLabel: A display area for a short text string or an image.
• JTextField: A text input component.
• JTextArea: A multi-line text input component.
• JPasswordField: A text input component for passwords.
• JCheckBox: A check box component.
• JRadioButton: A radio button component.
• JComboBox: A combo box component (drop-down list).
• JList: A list component.
• JOptionPane: Provides standard dialog boxes.
• JScrollBar: A scroll bar component.
• JMenuItem & JMenu: Menu components.

Java Event Handling

• Mechanism for handling user interactions (e.g., button clicks, mouse movements).
• Java Event classes and Listener interfaces.

Java Event Classes and Listener Interfaces

• ActionEvent, ActionListener.
• MouseEvent, MouseListener, MouseMotionListener.
• KeyListener, KeyListener.

Layout Manager

• Determines the layout of components in a container.
• Different layout managers include BorderLayout, FlowLayout, GridLayout, CardLayout, BoxLayout.

BorderLayout

• Arranges components in the north, south, east, west, and center regions.

FlowLayout

• Arranges components in a flow from left to right.

GridLayout

• Arranges components in a grid.

CardLayout

• Arranges components in a stack, where only one component is visible at a time.

BoxLayout

• Arranges components in a single row or column.

JDBC

• JDBC Introduction,JDBCDriver,DBConnectivitySteps ,ConnectivitywithOracleorMySqlDriverManager, ConnectionStatement,ResultSet,PreparedStatement, ResultSetMetaData,CallableStatement

JDBC Introduction

• Java Database Connectivity.
• API for connecting to and interacting with databases.

JDBC Driver

• Software component that enables a Java application to interact with a database.
• Different drivers for different databases (e.g., MySQL, Oracle).

DB Connectivity Steps

• Load the JDBC driver.
• Establish a connection.
• Create a statement.
• Execute the query.
• Process the result set.
• Close the connection.

Connectivity with Oracle or MySQL DriverManager

• Using DriverManager.getConnection() to establish a connection.
• Providing the database URL, username, and password.

Connection Statement

• Creating Statement, PreparedStatement, or CallableStatement objects from the Connection object.

ResultSet

• Represents the result of a database query.
• Used to retrieve data from the query result.

PreparedStatement

• Precompiled SQL statement.
• More efficient than Statement for executing the same query multiple times with different parameters.

ResultSetMetaData

• Provides information about the columns in a ResultSet.
• Used to get column names, types, and other properties.

CallableStatement

• Used to execute stored procedures in the database.
• Extends PreparedStatement and provides methods for handling input and output parameters.