Course Content
Java OOP
Java OOP
Default Methods
Abstract class vs Interface: The Interface Strikes Back!
Previously, methods with implementations could only exist in abstract classes, but starting from Java 8, they also appeared in interfaces.
Let's take a look at the syntax for declaring a default method:
We need default methods for the same purposes as regular methods in Java. We use them when we need an implementation in the method and when we want to implement only the interface without additional classes. Let's consider a small example using default methods:
Main
package com.example; public class Main { public interface Greeting { default void sayHello() { System.out.println("Hello from the interface!"); } void greet(String name); } public static class GreetingImpl implements Greeting { @Override public void greet(String name) { System.out.println("Hello, " + name + "!"); } } public static void main(String[] args) { GreetingImpl greetingImpl = new GreetingImpl(); greetingImpl.sayHello(); // Output: Hello from the interface! greetingImpl.greet("Alice"); // Output: Hello, Alice! } }
In this example, the interface Greeting
contains a default method sayHello()
with a default implementation. The class GreetingImpl
implements this interface and overrides the greet()
method. In the main method, an instance of GreetingImpl
is created and both methods are called.
Everything was clear?