Interface in Java

In Java, an interface is a collection of abstract methods and constants (static final variables). It defines a set of methods that a class implementing the interface must provide. An interface is similar to a class, but it cannot be instantiated directly. Instead, other classes can implement an interface, which means that they provide an implementation for all of the methods declared in the interface.

To define an interface in Java, you use the interface keyword followed by the name of the interface. Here's an example:

java
public interface Printable {
    void print();
}

In this example, the Printable interface declares a single abstract method called print(). Any class that implements the Printable interface must provide an implementation for this method.

To implement an interface in Java, you use the implements keyword followed by the name of the interface. Here's an example:

java
public class Printer implements Printable {
    public void print() {
        // implementation of the print method
    }
}

In this example, the Printer class implements the Printable interface by providing an implementation for the print() method.

Interfaces can also extend other interfaces, allowing you to build hierarchies of interfaces. Here's an example:

java
public interface Colorable {
    void setColor(String color);
}

public interface PrintableColorable extends Printable, Colorable {
    // no additional methods
}

public class ColorPrinter implements PrintableColorable {
    public void print() {
        // implementation of the print method
    }
    public void setColor(String color) {
        // implementation of the setColor method
    }
}

In this example, the Colorable interface declares a single method called setColor(). The PrintableColorable interface extends both the Printable and Colorable interfaces. Finally, the ColorPrinter class implements the PrintableColorable interface by providing implementations for both the print() and setColor() methods