Before Java SE 7, we have to write code to create new instances of generic types as follows: 

List<Integer> numbers = new ArrayList<Integer>();

 

Or more complex: 

Map<String, String> simpleMap = new HashMap<String, String>();

 

Or even more complex: 

Map<String, List<Integer>> complexMap = new HashMap<String, List<Integer>>();

Why do we have to declare the parameter types on both side? The parameter types on the right-hand side seem to be redundant, right? So in Java 7 and later, developer can now replace the right-hand side parameters with an empty set of parameters like this:

 

List<Integer> numbers = new ArrayList<>();

Map<String, String> simpleMap = new HashMap<>();

Map<String, List<Integer>> complexMap = new HashMap<>();

The angle brackets <> are informally called the diamond operator. The Java compiler can infer the types based on the left-hand side (thus the term type inference). This is a simple language improvement but it greatly simplifies generic instance creation (of course the old way still works) and saves us a lot of code!

 

Related Tutorials:

• What are Generics in Java
• How to write generic classes and methods in Java

 

Other Recommended Tutorials:

• 9 Rules about Constructors in Java
• 12 Rules and Examples About Inheritance in Java
• 12 Rules of Overriding in Java You Should Know
• 10 Java Core Best Practices Every Java Programmer Should Know
• Java Variables Passing Examples - Pass-by-value or Pass-by-reference?
• Understand Encapsulation in Java