| Types java app |
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| Data Types and Operators |
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| (Primitive Data Types) |
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| (Non-Primitive Data Types) |
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| Control Flow Statements |
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| Conditional Statements |
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| Looping Statements |
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| Branching Statements |
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| Object-Oriented Programming (OOP) |
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| Classes and Objects |
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| Inheritance |
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| Polymorphism |
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| Encapsulation |
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| Abstraction |
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| Exception Handling |
|---|
| Introduction to Exceptions |
|---|
| Collections Framework |
|---|
| Overview of Collections |
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| Commonly Used Collections |
|---|
| Iterators |
|---|
| Java I/O |
|---|
| File Handling |
|---|
| Serialization |
|---|
| Multithreading |
|---|
| Introduction to Threads |
|---|
| Thread Synchronization |
|---|
| GUI Programming with Swing |
|---|
| Introduction to Swing |
|---|
| Event Handling |
|---|
| Advanced Topics |
|---|
| Java Database Connectivity (JDBC) |
|---|
| JAVA CODE |
|---|
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Java Basics
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Working with Objects
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Arrays, Conditionals, and Loops
|
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Creating Classes and Applications in Java
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More About Methods
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Java Applet Basics
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Graphics, Fonts, and Color
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Simple Animation and Threads
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More Animation, Images, and Sound
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Managing Simple Events and Interactivity
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Creating User Interfaces with the awt
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Windows, Networking, and Other Tidbits
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Modifiers, Access Control, and Class Design
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Packages and Interfaces
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Exceptions
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Multithreading
|
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Streams and I/O
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Using Native Methods and Libraries
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Under the Hood
|
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Java Programming Tools
|
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Working with Data Structures in Java
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Advanced Animation and Media
|
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Fun with Image Filters
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Client/Server Networking in Java
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Emerging Technologies
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appendix A :- Language Summary
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appendix B :- Class Hierarchy Diagrams
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appendix C The Java Class Library
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appendix D Bytecodes Reference
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appendix E java.applet Package Reference
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appendix F java.awt Package Reference
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appendix G java.awt.image Package Reference
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appendix H java.awt.peer Package Reference
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appendix I java.io Package Reference
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appendix J java.lang Package Reference
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appendix K java.net Package Reference
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appendix L java.util Package Reference
|
Abstract classes and methods are essential features in Java, used to create blueprints for other classes. They cannot be instantiated on their own but must be extended by other classes. Here’s a detailed explanation of both:
Abstract Classes
Definition: An abstract class in Java is a class that is declared with the
abstractkeyword. It can have abstract methods (methods without a body) as well as concrete methods (regular methods with a body).Purpose: Abstract classes are used to provide a common base class for other classes. They define a template for future derived classes. This allows for code reusability and ensures a consistent design.
Characteristics:
- Cannot be instantiated directly.
- Can have both abstract and concrete methods.
- Can have member variables.
- Can have constructors, which are called when a concrete subclass is instantiated.
- Can extend only one class (single inheritance).
4. Syntax:
public abstract class Animal {
// Member variables
private String name;
// Constructor
public Animal(String name) {
this.name = name;
}
// Concrete method
public void eat() {
System.out.println(name + " is eating.");
}
// Abstract method
public abstract void makeSound();
}
Abstract Methods
Definition: An abstract method is a method that is declared without an implementation. It is declared using the
abstractkeyword within an abstract class.Purpose: Abstract methods are meant to be overridden in subclasses. They provide a template that subclasses must follow, ensuring that the subclass provides a specific implementation of the method.
Characteristics:
- Cannot have a body (no implementation).
- Must be implemented by any non-abstract subclass.
- Declared within an abstract class.
4. Syntax:
public abstract class Animal {
// Abstract method
public abstract void makeSound();
}
public class Dog extends Animal {
// Implementing abstract method
@Override
public void makeSound() {
System.out.println("Bark");
}
}
Example in Depth
Here’s a comprehensive example to illustrate how abstract classes and methods work together:
// Abstract class
public abstract class Shape {
// Abstract method
public abstract double area();
// Concrete method
public void display() {
System.out.println("This is a shape.");
}
}
// Concrete subclass
public class Circle extends Shape {
private double radius;
public Circle(double radius) {
this.radius = radius;
}
@Override
public double area() {
return Math.PI * radius * radius;
}
}
// Concrete subclass
public class Rectangle extends Shape {
private double width;
private double height;
public Rectangle(double width, double height) {
this.width = width;
this.height = height;
}
@Override
public double area() {
return width * height;
}
}
// Main class to test the implementation
public class Main {
public static void main(String[] args) {
Shape circle = new Circle(5);
Shape rectangle = new Rectangle(4, 6);
circle.display();
System.out.println("Circle Area: " + circle.area());
rectangle.display();
System.out.println("Rectangle Area: " + rectangle.area());
}
}
Key Points
- Flexibility and Extensibility: Abstract classes and methods provide a way to define interfaces that subclasses must implement, offering flexibility and extensibility in code design.
- Partial Implementation: Abstract classes allow you to provide partial implementation, which can be shared among multiple subclasses.
- Common Behavior: Abstract classes can include methods that implement common behavior shared by all subclasses.
In summary, abstract classes and methods in Java are powerful tools for creating a flexible and maintainable object-oriented design. They allow for defining a common template while enforcing specific behavior in subclasses.
