Understanding Java Interfaces

Textual Information

An interface in Java defines a contract for how classes interact. It contains public method signatures, requires implementing classes to provide method implementations, and can include default and static methods that are not inherited.

Click to learn more

Video Information

Code Snippets

    // interface example
    public interface Animal {
        void eat();  
        void sleep(); 
    }

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

Quiz

Test your knowledge on Java interfaces:

1. What is an interface in Java?

A class that cannot be instantiated.
A blueprint that defines a contract for classes to implement.
A way to inherit methods from multiple classes.
None of the above.

2. Which keyword is used to implement an interface in Java?

abstract
extends
implements
interface

3. What must a class do when it implements an interface?

Only implement some of the methods.
Provide implementations for all the interface's methods.
Declare the interface as a superclass.
None of the above.

Java Interface Details

Definition and Purpose: Specifies contracts for class interactions, typically used where two systems interact (e.g., GUI or API).

Structure:
- Contains public method signatures and return types.
- No fields except constants (public, final, and static by default).

Method Implementation:
- Classes implementing an interface must implement all methods.
- Default and static methods can have method bodies.
- Static methods in an interface are called using the interface name and are not inherited.

Multiple Interface Implementation: Classes can implement multiple interfaces (separated by commas).

Default Methods: If two interfaces provide default methods, explicit implementation in the class is required.

Interface Characteristics: Does not specify the internal implementation of classes.