Default Methods =
The main reason to introduce default methods is that if at some point we need to add a method to an existing interface, we can add a method without changing the existing implementation classes. To support lambda expressions in collections API and to enhance.In this way, the interface is still compatible with older versions.
- Before Java 8 in interfaces we are able to declare only abstract methods.
- If we declare a method without abstract that will be treated as abstract by default.
- These methods won’t have body means implementations.
- The class which is implementing this interface need to provide body / implementation for this abstract methods.
- Now with java 8 default methods we can add methods to interface without disturbing existing functionality.
- So instead of overriding now we can inherit these default methods from interfaces.
- We can override java 8 default method.
- Defaults methods are also known as defender methods or virtual extension methods.
Example -
In interface MyInterface.java
public interface MyInterface {
String text = "Hello";
void sayHello();
default void saySomething() {
System.out.println("In MyInterface");
}
}In class MyInterfaceImpl.java
public class MyInterfaceImpl implements MyInterface{
@Override
public void sayHello() {
System.out.println(MyInterface.text);
}
public static void main(String[] args) {
MyInterfaceImpl myInterfaceImpl = new MyInterfaceImpl();
myInterfaceImpl.sayHello(); // calling implemented method
myInterfaceImpl.saySomething(); // calling inherited method
MyInterface myInterface = new MyInterfaceImpl();
myInterface.saySomething(); // calling using interface name
}
}Output
Hello
In MyInterface
In MyInterface