Java 8: Default Methods

Default methods are introduced in Java 8 to use with interfaces. This helps older interfaces to support lambda expressions without breaking their implementations.

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For example List interface do not have forEach method as this added in Java 8, adding it will break the implementations. By adding this a default implementation these old implementations also can support forEach method automatically.

public interface vehicle {

   default void print() {
      System.out.println("I am a vehicle!");
   }
}

As this new implementation can be a problem when used in multiple inheritance scenarios. If both has same method then we may have to create a new method to override both.

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An interface can also have static helper methods from Java 8 onwards.

public interface vehicle {

   default void print() {
      System.out.println("I am a vehicle!");
   }
	
   static void blowHorn() {
      System.out.println("Blowing horn!!!");
   }
}

Ref: https://www.tutorialspoint.com/java8/java8_default_methods.htm

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