Tags: Interface

In my previous article I explained Difference between Abstract class and Interface in Java. It gives you insight on interface in Java. And Now...

What is @FunctionInterface?
In Simple Term...

Characteristics of Functional Interface.
- You can have only one abstract method in Functional Interface.
- You can have default methods and static methods in Functional Interface because they are not abstract.
- You can have public methods of java.lang.Object class in Functional Interface because these method won't count towards Functional Interface's abstract method.

Source Code

/**
 * Any media that is <code>Playable</code> in mobile should implement this interface.
 */
@FunctionalInterface
public interface Playable {

    public void play(String file);

    /* public method of java.lang.Object class */
    @Override
    public boolean equals(Object obj);

    /* public method of java.lang.Object class */
    @Override
    public String toString();

    /* static method to get default player */
    static String defaultPlayer() {
        return "Google Play";
    }

    /* default method to identify file type */    
    default String fileType(String strFilename) {
        if (strFilename == null || strFilename.isEmpty()) {
            return "Provide valid filename";
        }

        if (strFilename.endsWith(".mp3")) {
            return "Audio File";
        } else if (strFilename.endsWith(".mp4")) {
            return "Video File";
        } else {
            return "File not supported";
        }
    }
}

Source Code(Using in Lambda Expression)

public class Motorola {

   public static void main(String[] args) {
      /* Implementing Playable interface using Lambda Expression */
      Playable playable = (String file) -> { System.out.println("Playing Music: " + file); };

      /* Call play */
      playable.play("Pitbull - Give Me Everything ft. Ne-Yo, Afrojack, Nayer.mp4");

      /* Using Interface as parameter in method */
      MusicPlayer((file) -> { System.out.println("Playing Music: " + file); }, "Pitbull - International Love ft Chris Brown.mp4");
   }

   /* Method using Playable interface to play music file */
   public static void MusicPlayer(Playable playable, String file) {
      playable.play(file);
   }
}

Output

Playing Music: Pitbull - Give Me Everything ft. Ne-Yo, Afrojack, Nayer.mp4
Playing Music: Pitbull - International Love ft Chris Brown.mp4

Myth about @FunctionInterface and Lambda Expression
Many developers think if we want to use any Interface in Lambda Expression then it must be Functional Interface. Its completely wrong!

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Java 8
default and static method in Java Interface

Tags: Interface