Java interfaces used to have only abstract methods until JDK 8, which introduced the ability to add default and static methods.

During application enhancement or maintenance, it may become necessary to add new methods to an interface. This would typically force all implementing classes to change and implement the new abstract methods.

Thus we can add these default methods to existing interfaces without breaking the code and changing old implementation classes.

interface DefaultMethod {
    public default void defMethod() {
        System.out.println("Default Method");
    }
}

public class TestDefault implements DefaultMethod {
    public static void main(String[] args) {
        TestDefault t = new TestDefault();
        t.defMethod();
    }
}
          

Likewise, you can define default static methods in an interface, with the restriction that static methods cannot be overridden.