What is the difference between extends and implements in Java?

[system]

In Java, extends and implements are both keywords used to achieve inheritance, but they are used in different contexts and have distinct purposes.

extends Keyword:

• Purpose: The extends keyword is used for class inheritance. It allows a class to inherit from another class or an abstract class.
• Single Inheritance: A class can only extend one class (single inheritance).
• Usage: When a class extends another class, it inherits the fields and methods of the parent class.
• Example: Extending a class or abstract class.

Example:

class Animal {
    void eat() {
        System.out.println("This animal eats food.");
    }
}
class Dog extends Animal {  
void bark() {
System.out.println("The dog barks.");
}
}
public class Main {
public static void main(String args) {
Dog dog = new Dog();
dog.eat();  // Inherited from Animal
dog.bark(); // Defined in Dog
}
}

• In this example: Dog class extends Animal, inheriting its behavior.

implements Keyword:

• Purpose: The implements keyword is used for interface inheritance. It allows a class to implement one or more interfaces.
• Multiple Inheritance: A class can implement multiple interfaces, achieving a form of multiple inheritance.
• Usage: When a class implements an interface, it must provide implementations for all the abstract methods declared in the interface.
• Example: Implementing interfaces.

Example:

interface Animal {
    void eat();
}
interface Bird {  
void fly();
}
class Bat implements Animal, Bird {
public void eat() {
System.out.println("The bat eats insects.");
}

public void fly() {
System.out.println("The bat flies.");
}

}
public class Main {
public static void main(String args) {
Bat bat = new Bat();
bat.eat();  // Implements Animal interface
bat.fly();  // Implements Bird interface
}
}

• In this example: Bat class implements both Animal and Bird interfaces and provides implementations for their methods.

Key Differences:

\| Aspect \| extends \| implements \|

\|---------------------\|---------------------------------------------------\|---------------------------------------------------\|

\| Used for \| Extending a class (or abstract class) \| Implementing an interface \|

\| Type of Inheritance \| Single inheritance (class can extend only one class) \| Multiple inheritance (class can implement multiple interfaces) \|

\| Method Implementation \| Can inherit methods, and override if needed. \| Must provide implementations for all interface methods. \|

\| Keyword \| Used with classes or abstract classes \| Used with interfaces \|

\| Example \| class Dog extends Animal {} \| class Bat implements Animal, Bird {} \|

Summary:

• extends is used for class inheritance (single inheritance).
• implements is used for interface inheritance (multiple inheritance).