Java Interface

In Java, an interface is a reference type that defines a set of abstract methods and constants. Here's an overview of interfaces:

Definition:

• An interface is declared using the interface keyword, similar to a class declaration.
• It contains method signatures (without method bodies) and constant declarations.
• Example:

interface Animal {
    void makeSound(); // Abstract method
    int LEGS = 4; // Constant
}

Abstract Methods:

• Interfaces can have abstract methods, which are methods without a body.
• Classes implementing the interface must provide concrete implementations for all abstract methods.
• Example:

interface Animal {
    void makeSound();
}

Constants:

• Interfaces can also contain constants, which are implicitly public, static, and final.
• Constants can be accessed using the interface name.
• Example:

interface Animal {
    int LEGS = 4;
}

Implementing Interfaces:

• Classes implement interfaces using the implements keyword.
• A class can implement multiple interfaces.
• Example:

class Dog implements Animal {
    public void makeSound() {
        System.out.println("Woof");
    }
}

Default Methods (Java 8 and later):

• Interfaces can have default methods with a default implementation.
• Default methods allow adding new functionality to existing interfaces without breaking backward compatibility.
• Example:

interface Animal {
    default void sleep() {
        System.out.println("Animal is sleeping");
    }
}

 

Summary

Interfaces provide a way to achieve abstraction and define contracts for classes to implement. They play a crucial role in achieving loose coupling and promoting code reusability in Java applications.