How to instantiate a collection in Java using Generics?

Question

Whats the best way:

Set<String> myStringSet = new HashSet();

Or

Set<String> myStringSet = new HashSet<String>();

None of the above?

Does it matter?

Check this question and accepted answer: http://stackoverflow.com/questions/4166966/what-is-the-point-of-the-diamond-operator-in-java-7 — Ernesto Campohermoso, Dec 13 '11 at 23:16
In Java SE 7 (OUT NOW!) `Set myStringSet = new HashSet<>();` — Tom Hawtin - tackline, Dec 14 '11 at 00:21

score 5 · Accepted Answer · answered Dec 13 '11 at 23:13

5

The latter:

Set<String> myStringSet = new HashSet<String>();

See the Java documentation on generic types for more information.

answered Dec 13 '11 at 23:13

Jon Newmuis

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Just start using the untyped version...when you realize all of the annoying casts you have to do, you'll start using typed Collections! – James Bassett Dec 14 '11 at 01:07

score 3 · Answer 2 · answered Dec 13 '11 at 23:18

3

You should always initialize collection with generic type

Set<String> myStringSet = new HashSet<String>();

Otherwise you will get a warning

Type safety: The expression of type HashSet needs unchecked conversion 
to conform to Set <String>.

answered Dec 13 '11 at 23:18

Desmond Zhou

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score 0 · Answer 3 · answered Dec 13 '11 at 23:23

The second is the best and safest way to proceed.

Set<String> myStringSet = new HashSet(); will compile and give a ...uses unchecked or unsafe operations. warning. This comes up in Java 5 and later, if you're using collections without generic type specifiers (HashSet() instead of HashSet<String>()).

Omitting the generic type specifier will disable the compiler from checking that you're using the HashSet in a type-safe way, using generics.

How to instantiate a collection in Java using Generics?

3 Answers3