| 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 |
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| Introduction to Exceptions |
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| Collections Framework |
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| Overview of Collections |
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| Commonly Used Collections |
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| Iterators |
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| Java I/O |
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| File Handling |
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| Serialization |
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| Multithreading |
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| Introduction to Threads |
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| Thread Synchronization |
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| GUI Programming with Swing |
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| Introduction to Swing |
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| Event Handling |
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| Advanced Topics |
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| Java Database Connectivity (JDBC) |
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| 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
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In Java, classes are the fundamental building blocks for creating objects and defining their behaviors. A class is a blueprint that defines the attributes (fields) and behaviors (methods) that the objects created from the class can have. Here is a detailed explanation of how to define classes in Java:
Basic Structure of a Class
A class in Java is defined using the class keyword, followed by the class name and a pair of curly braces containing the class body. Here’s a basic example:
public class Car {
// Fields (or instance variables)
String color;
String model;
int year;
// Constructor
public Car(String color, String model, int year) {
this.color = color;
this.model = model;
this.year = year;
}
// Methods
public void startEngine() {
System.out.println("The engine is starting.");
}
public void stopEngine() {
System.out.println("The engine is stopping.");
}
}
Fields
Fields (also called instance variables) hold the data or state of an object. They are defined within the class but outside any method or constructor. Fields can have various access modifiers such as private, protected, public, or package-private (default).
private String color;
public String model;
int year; // package-private by default
Constructors
Constructors are special methods that are called when an object is instantiated. They initialize the object’s state. A constructor has the same name as the class and does not have a return type.
public Car(String color, String model, int year) {
this.color = color;
this.model = model;
this.year = year;
}
Methods
Methods define the behavior of the objects created from the class. Methods can perform operations, modify the object’s state, or return values.
public void startEngine() {
System.out.println("The engine is starting.");
}
public void stopEngine() {
System.out.println("The engine is stopping.");
}
Access Modifiers
Access modifiers control the visibility of classes, fields, methods, and constructors. The most common access modifiers are:
public: The member is accessible from any other class.private: The member is accessible only within its own class.protected: The member is accessible within its own package and by subclasses.- Package-private (default): The member is accessible only within its own package.
Encapsulation
Encapsulation is a principle where the internal state of an object is hidden from the outside world and can only be accessed through public methods. This is typically achieved by making fields private and providing public getter and setter methods.
public class Car {
private String color;
private String model;
private int year;
public Car(String color, String model, int year) {
this.color = color;
this.model = model;
this.year = year;
}
public String getColor() {
return color;
}
public void setColor(String color) {
this.color = color;
}
public String getModel() {
return model;
}
public void setModel(String model) {
this.model = model;
}
public int getYear() {
return year;
}
public void setYear(int year) {
this.year = year;
}
public void startEngine() {
System.out.println("The engine is starting.");
}
public void stopEngine() {
System.out.println("The engine is stopping.");
}
}
Inheritance
Inheritance is a mechanism where one class (subclass) inherits the fields and methods of another class (superclass). This promotes code reuse.
public class ElectricCar extends Car {
private int batteryLife;
public ElectricCar(String color, String model, int year, int batteryLife) {
super(color, model, year); // Call the constructor of the superclass
this.batteryLife = batteryLife;
}
public int getBatteryLife() {
return batteryLife;
}
public void setBatteryLife(int batteryLife) {
this.batteryLife = batteryLife;
}
public void chargeBattery() {
System.out.println("The battery is charging.");
}
}
Polymorphism
Polymorphism allows objects to be treated as instances of their parent class rather than their actual class. This can be achieved through method overriding and interfaces.
public class Car {
public void startEngine() {
System.out.println("The car engine is starting.");
}
}
public class ElectricCar extends Car {
@Override
public void startEngine() {
System.out.println("The electric car engine is starting silently.");
}
}
public class TestCar {
public static void main(String[] args) {
Car myCar = new ElectricCar();
myCar.startEngine(); // Output: The electric car engine is starting silently.
}
}
Abstract Classes and Interfaces
Abstract classes and interfaces are used to define methods that must be implemented by subclasses or implementing classes.
public abstract class Vehicle {
public abstract void startEngine(); // Abstract method
public void stopEngine() {
System.out.println("The engine is stopping.");
}
}
public interface Drivable {
void drive(); // Interface method (implicitly public and abstract)
}
public class Car extends Vehicle implements Drivable {
@Override
public void startEngine() {
System.out.println("The car engine is starting.");
}
@Override
public void drive() {
System.out.println("The car is driving.");
}
}
Summary
Defining classes in Java involves specifying the class name, fields, constructors, and methods. Access modifiers control the visibility of these members, and principles like encapsulation, inheritance, and polymorphism help in creating robust and reusable code. Abstract classes and interfaces provide a way to enforce certain behaviors across different classes.
