Diamond Operator - Java9

// before Java 7, explicit generic type declaration required
List<String> myList = new ArrayList<String>();

// since Java 7, diamond operator can be used
List<String> list = new ArrayList<>();

• Java 7 Diamond Operator was not possible for anonymous inner classes. 
• Since Java 9, diamond operator can be used in anonymous inner classes

Simple Example

DiamondOperatorMain.java

 
package com.java9r;

/**
 * @author Ravi
 *
 */
public class DiamondOperatorMain {

 /**
  * @param args
  */
 public static void main(String[] args) {

  DiamondOperator<Integer> diamond = new DiamondOperator<>() {

   public void testMethod() {
    System.out.println("Test Method");
   }
  };
  diamond.testMethod();

 }
}

DiamondOperator.java

 package com.java9r;

/**
 * @author Ravi
 *
 */
public interface DiamondOperator<T> {
 void testMethod();

}

Output

Test Method

Diamond Operator Using Abstract class Example

DiamondOperatorAbstractMain.java

 package com.java9r;

/**
 * @author Ravi
 *
 */
public class DiamondOperatorAbstractMain {

 /**
  * @param args
  */
 public static void main(String[] args) {

  DiamondOperatorAbstract<Integer> diamondOperator1 = new DiamondOperatorAbstract<>(1) { // Anonymous Class

   @Override
   public void handle() {
    System.out.println("diamondOperator 1 > " + getContent());
   }
  };
  diamondOperator1.handle();

  DiamondOperatorAbstract<? extends Integer> diamondOperator2 = new DiamondOperatorAbstract<>(3) { // Anonymous Class

   @Override
   void handle() {
    System.out.println("diamondOperator 2 > " + getContent());
   }
  };
  diamondOperator2.handle();

  DiamondOperatorAbstract<?> diamondOperator3 = new DiamondOperatorAbstract<>("Three") { // Anonymous Class

   @Override
   void handle() {
    System.out.println("diamondOperator 3 > " + getContent());
   }
  };
  diamondOperator3.handle();

 }
}

DiamondOperatorAbstract.java

 package com.java9r;

/**
 * @author Ravi
 *
 */
public abstract class DiamondOperatorAbstract<T> {
 private T content;

 public DiamondOperatorAbstract(T content) {
  this.content = content;
  System.out.println("Constructor for Diamond Operator Abstract : " + content.toString());
 }

 public T getContent() {
  return content;
 }

 public void setContent(T content) {
  this.content = content;
 }

 abstract void handle();

}

Output

Constructor for Diamond Operator Abstract : 1
diamondOperator 1 > 1
Constructor for Diamond Operator Abstract : 3
diamondOperator 2 > 3
Constructor for Diamond Operator Abstract : Three
diamondOperator 3 > Three