通用实例创建的Java7类型推断？

Question

How we can use Java 7 Type inference for generic instance creation feature ? What all benefits to use this new style?

Answer 1

This is also known as the diamond operator. It saves you from having to write the generic type arguments on the instantiation of a generic type. The type arguments of the instantiated generic type are inferred from the type arguments present on the declaration.

ArrayList<String> list = new ArrayList<>();

Instead of:

ArrayList<String> list = new ArrayList<String>();

Answer 2

No. The diamond syntax is merely a shorthand in coding/typing. These two are the same

List<String> a = new ArrayList<String>();  
List<String> a = new ArrayList<>();  

They are treated the same for the compiling process, hints to the compiler. Even before type erasure, they are treated the same. It's literally just a convenience for you.

Answer 3

It's just less typing.

From the docs :

For example, consider the following variable declaration:

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

In Java SE 7, you can substitute the parameterized type of the constructor with an empty set of type parameters (<>):

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

Unfortunately, you still have to type the diamond .