When to implement and extend? [closed]

Answer 1

Implement:

Interfaces are abstract classes, so you can only declare things. A class implements an interface. You can implement multiple interfaces.

Extend:

You extend classes when you want a more specific version of a class.

Example:

// Contract: a pet should play
public interface Pet {
    public void play(); 
}

// An animal eats and sleeps
class Animal {
    public void eat();
    public void sleep();
}


public class Camel extends Animal {

}

public class Dog extends Animal implements Pet {    
    public void play() {...}
}

Both Camel and Dog are animals, so they extend Animal class. But only the Dog is a specific kind of Animal that also can be a Pet