Java 9 Diamond Operator With Example Posted: March 31, 2023 @ 6:45 am

How to declare Diamond Operator in Java?

// This is prior to Java 7. We have to explicitly mention the generic type //on the right side as well. List<String> myList = new ArrayList<String>(); // Java 7 onwards, no need to mention generic type on the right side List<String> myList = new ArrayList<>();

Problem with Diamond Operator while using Annonymous Inner class:

Until Java 8 Diamond Operator allow us to use in normal class only. This Diamond Operator is not allowed to anonymous inner class in Java.

Example:

abstract class MyTest<T>{ abstract T msg(T a, T b); } public class Example { public static void main(String[] args) { MyTest<String> t=new MyTest<>() { String msg(String a, String b) { return a+b; } }; String output = t.msg("Hello"," Programmer"); System.out.println(output); } }

Output:

Example.

java:6: error: cannot infer type arguments for MyTest<T> ???????MyTest<String> t=new MyTest<>() { reason: cannot use '<>' with anonymous inner classes where T is a type-variable: T extends Object declared in class MyTest 1 error

We got a compilation error when we ran this above example until Java 8.

Java 9 - Diamond Operator Enhancement:

From Java 9 onwards Diamond Operator is allowed to use in anonymous classes also. This is the enhancement of Diamond Operator in Java 9.

Example:

abstract class MyTest<T>{ abstract T msg(T a, T b); } public class Example { public static void main(String[] args) { MyTest<String> t=new MyTest<>() { String msg(String a, String b) { return a+b; } }; String output = t.msg("Hello"," Programmer"); System.out.println(output); } }

Output:

Hello Programmer

Conclusion:

In this topic, we learnt about Diamond Operator in Java, Diamond Operator anonymous inner class problem until Java 8 and Diamond Operator enhancement in Java 9

Author:

SpringJava

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