What are some examples of interfaces in Java OOP?

What are some examples of interfaces in Java OOP?

In Java, an interface is a reference type, similar to a class, that can contain only constants, method signatures, default methods, static methods, and nested types. Here are a few examples:

1. Animal Interface: An interface that defines methods like eat() and sleep(). Classes like Dog and Cat can implement this interface.
2. Vehicle Interface: This could have methods like start(), stop(), and accelerate(), which can be implemented by classes like Car and Bike.
3. Shape Interface: An interface with methods like draw() and area(), which can be implemented by classes like Circle and Rectangle.

Can you explain how to implement an interface in a class?

Sure! To implement an interface in a class, you use the implements keyword. Here's a simple example:

interface Animal {
    void eat();
    void sleep();
}

class Dog implements Animal {
    public void eat() {
        System.out.println("Dog is eating");
    }
    public void sleep() {
        System.out.println("Dog is sleeping");
    }
}

In this example, the Dog class implements the Animal interface and provides concrete implementations for the eat() and sleep() methods.

What happens if a class does not implement all methods of an interface?

If a class does not implement all the methods of an interface, it must be declared as an abstract class. This means that the class cannot be instantiated directly, and any subclass must implement the remaining methods. Here's an example:

abstract class Animal {
    abstract void eat();
    abstract void sleep();
}

class Cat extends Animal {
    void eat() {
        System.out.println("Cat is eating");
    }
    // sleep() method is not implemented here
}

Can interfaces extend other interfaces?

Yes, interfaces can extend other interfaces in Java. When an interface extends another interface, it inherits all the abstract methods of the parent interface. Here's an example:

interface Animal {
    void eat();
}

interface Pet extends Animal {
    void play();
}

class Dog implements Pet {
    public void eat() {
        System.out.println("Dog is eating");
    }
    public void play() {
        System.out.println("Dog is playing");
    }
}