Use from empty type parameters?

Question

I was recently porting a Java 7 project down to Java 6 and I a had some Arraylists being initialized with empty type parameters.

Of course it gave quite a few errors because of it only being allowed in Java 7

So then I was wondering; What use do I get from using empty type parameters?

ex.: new Arraylist <>();

That means the parameter type can be resolved from context. It's just eye candy so that it's faster to write. — MightyPork, Jul 12 '14 at 09:12

score 0 · Answer 1 · answered Jul 12 '14 at 09:13

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It is called generics. It is a compile time concept and is used for type safety. You can take a look about generics in documentation.

If you use

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

i.e. with no generics ON the RHS then it is similar as saying

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

This is just a feature added in Java 7. As stated previously this being a compile time concept the generics of reference variable is what matters and not of actual object (created with new/RHS)

answered Jul 12 '14 at 09:13

Aniket Thakur

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This question is about diamond notation, not generics in general. – Boris the Spider Jul 12 '14 at 09:17
In context of `new Arraylist <>();` generics come into picture. – Aniket Thakur Jul 12 '14 at 09:18

score 0 · Answer 2 · answered Jul 12 '14 at 09:17

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It's called diamond operator and infers the generic type from the left hand side, if possible. Saves you a few keystrokes and was introduced with Java 7 (project coin).

answered Jul 12 '14 at 09:17

atamanroman

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Use from empty type parameters?

2 Answers2