| 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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Method overriding in Java is a feature that allows a subclass (child class) to provide a specific implementation for a method that is already defined by its superclass (parent class). This is a fundamental aspect of object-oriented programming that supports polymorphism and dynamic method dispatch. Here’s a detailed explanation of method overriding in Java:
Key Concepts of Method Overriding
Inheritance: Method overriding can only occur in the context of inheritance. A subclass inherits methods from a superclass and can override those methods to change their behavior.
Same Method Signature: The method in the subclass must have the same name, return type, and parameters as the method in the superclass. If there is any difference in the method signature, it is not considered an override but an overload.
Access Modifiers: The access level of the overriding method cannot be more restrictive than the method it overrides. For example, if the superclass method is
protected, the overriding method in the subclass cannot beprivate. It can, however, beprotectedorpublic.Annotations: The
@Overrideannotation is commonly used in Java to indicate that a method is intended to override a method in the superclass. This helps catch errors at compile time, such as if the method signature does not match.Instance Methods: Only instance methods can be overridden. Static methods belong to the class rather than any instance, so they cannot be overridden but can be hidden (though this is generally discouraged).
Constructor: Constructors cannot be overridden.
Example of Method Overriding
Here’s a simple example to illustrate method overriding:
// Superclass
class Animal {
void makeSound() {
System.out.println("Animal makes a sound");
}
}
// Subclass
class Dog extends Animal {
@Override
void makeSound() {
System.out.println("Dog barks");
}
}
public class TestOverride {
public static void main(String[] args) {
Animal myAnimal = new Animal();
Animal myDog = new Dog();
myAnimal.makeSound(); // Output: Animal makes a sound
myDog.makeSound(); // Output: Dog barks
}
}
Detailed Points
Polymorphism: In the example above, ‘
myDog‘ is of type ‘Animal‘ but points to an instance of ‘Dog‘. When ‘makeSound()‘ is called on ‘myDog‘, the overridden method in ‘Dog‘ is executed. This demonstrates polymorphism, where the call to’makeSound()‘ resolves to the’Dog‘s version of the method at runtime.Super Keyword: Sometimes, it is useful to call the superclass method within the overriding method. This can be done using the ‘
super‘ keyword.
class Dog extends Animal {
@Override
void makeSound() {
super.makeSound(); // Calls the method from Animal class
System.out.println("Dog barks");
}
}
3. Final Methods: If a method is declared as ‘final‘ in the superclass, it cannot be overridden by subclasses.
class Dog extends Animal {
@Override
void makeSound() {
super.makeSound(); // Calls the method from Animal class
System.out.println("Dog barks");
}
}
3. Final Methods: If a method is declared as ‘final‘ in the superclass, it cannot be overridden by subclasses.
class Animal {
final void makeSound() {
System.out.println("Animal makes a sound");
}
}
class Dog extends Animal {
// Compilation error: cannot override final method
@Override
void makeSound() {
System.out.println("Dog barks");
}
}
4. Abstract Methods: Abstract methods in an abstract class must be overridden in the subclass.
abstract class Animal {
abstract void makeSound();
}
class Dog extends Animal {
@Override
void makeSound() {
System.out.println("Dog barks");
}
}
5. Covariant Return Types: Since Java 5, it is allowed to override a method and change its return type to a subtype of the original return type.
class Animal {
Animal getInstance() {
return new Animal();
}
}
class Dog extends Animal {
@Override
Dog getInstance() {
return new Dog();
}
}
Best Practices
- Always use the
@Overrideannotation when overriding a method. It improves code readability and helps catch errors at compile time. - Ensure the overriding method provides additional functionality or modifies the behavior of the superclass method in a meaningful way.
- Be cautious with the use of
superto call superclass methods, as it can lead to tightly coupled code if not used judiciously. - Consider the use of
finalandabstractkeywords to control which methods can and cannot be overridden in subclasses.
Method overriding is a powerful feature in Java that, when used correctly, allows for flexible and reusable code. It is a cornerstone of polymorphism, enabling objects to be treated as instances of their parent class while still behaving in ways specific to their actual subclass.
