| 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, instance variables and instance methods are fundamental concepts that form the backbone of object-oriented programming (OOP). Here, I’ll explain each in detail:
Instance Variables
Instance variables are non-static fields that are declared inside a class but outside any method, constructor, or block. Each instance (or object) of the class has its own copy of these variables
Characteristics of Instance Variables:
- Scope: They are accessible to all methods, constructors, and blocks within the class.
- Lifetime: They exist for as long as the object is in memory.
- Default Values: If not initialized explicitly, instance variables are initialized with default values (e.g., ‘
0‘ for integers, ‘null‘ for objects). - Accessibility: They can have access modifiers like ‘
private‘, ‘protected‘,’public‘, or default (package-private), determining their visibility.
Example:
public class Car {
// Instance variables
private String color;
private String model;
private int year;
// Constructor
public Car(String color, String model, int year) {
this.color = color;
this.model = model;
this.year = year;
}
// Getter and Setter methods
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;
}
}
In this example, ‘color‘,’ model‘, and ‘year‘ are instance variables. Each ‘Car‘ object will have its own values for these fields.
Instance Methods
Instance methods are methods that belong to an instance of a class. They can access instance variables and other instance methods directly. These methods operate on the instance of the class, meaning they require an object to be called.
Characteristics of Instance Methods:
- Access to Instance Variables: They can directly access and modify instance variables.
- Invocation: They are called on objects of the class.
- Access Modifiers: They can be declared with any access modifier (
private,protected,public, or default). - Polymorphism: Instance methods can be overridden in subclass implementations, allowing for dynamic method dispatch.
Example:
public class Car {
// Instance variables
private String color;
private String model;
private int year;
// Constructor
public Car(String color, String model, int year) {
this.color = color;
this.model = model;
this.year = year;
}
// Instance method
public void displayDetails() {
System.out.println("Car Model: " + model);
System.out.println("Color: " + color);
System.out.println("Year: " + year);
}
// Main method to demonstrate instance methods
public static void main(String[] args) {
Car myCar = new Car("Red", "Toyota", 2021);
myCar.displayDetails(); // Calling the instance method
}
}
In this example, ‘displayDetails()‘ is an instance method that prints the details of the ‘Car‘ object. It directly accesses the instance variables ‘color‘, ‘model‘, and ‘year‘.
Summary
- Instance Variables: These are data members of a class, and each object has its own copy. They define the properties of an object.
- Instance Methods: These define the behavior of an object and can manipulate instance variables. They require an object of the class to be invoked.
Together, instance variables and instance methods define the state and behavior of objects, enabling the creation of robust and modular Java applications.
