Java 8 - include static methods inside interfaces

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This allows utilities that rightly belong in the interface, which are typically things that manipulate that interface, or are general-purpose tools:

// onjava/Operations.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
package onjava;

import java.util.*;

public interface Operations {
  void execute();

  static void runOps(Operations... ops) {
    for (Operations op : ops) op.execute();
  }

  static void show(String msg) {
    System.out.println(msg);
  }
}

 above code is a version of the Template Method design pattern.

// interfaces/Machine.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.

import java.util.*;
import onjava.Operations;

class Bing implements Operations {
  public void execute() {
    Operations.show("Bing");
  }
}

class Crack implements Operations {
  public void execute() {
    Operations.show("Crack");
  }
}

class Twist implements Operations {
  public void execute() {
    Operations.show("Twist");
  }
}

public class Machine {
  public static void main(String[] args) {
    Operations.runOps(new Bing(), new Crack(), new Twist());
  }
}
/* Output:
Bing
Crack
Twist
*/

Here you see the different ways to create Operations: an external class(Bing), an anonymous class, a method reference, and lambda expressions——which certainly appear to be the nicest solution here.

references:

1. On Java 8 - Bruce Eckel

2. https://github.com/wangbingfeng/OnJava8-Examples/blob/master/onjava/Operations.java

3. https://github.com/wangbingfeng/OnJava8-Examples/blob/master/interfaces/Machine.java

4. https://howtodoinjava.com/java8/lambda-expressions/