Java Tips: Initializing Collection

Especially in unit test, it is common case that we have to initialize an array or a collection.

Well, for array, it’s OK… A simple code that we know can solve the problem:

String[] s = new String [] {"1", "2"};

But how about Collection? Normal way to initialize collection is something like this (which pretty ugly):

List<String> s = new ArrayList<String>();
s.add("1");
s.add("2");

I hardly find an elegant solution until I see this post. There are at least three better solution for the case.

First solution:

List<String> s = new ArrayList<String>() {{ add("1"); add("2"); }};

Which unfortunately, doesn’t pass Java Code Convention (that is, if you format the code, it will become uglier than the original).

List<String> s = new ArrayList<String>() {
   {
      add("1");
      add("2");
   }
};

Second solution:

List<String> s = Arrays.asList(new String[]{"1", "2"});

This solution is the best if you use Java 1.4 or before. But if you use Java 5, the third is more elegant:

List<String> s = Arrays.asList("1", "2");

Great!

EDIT: this solution will create a fixed size BUT modifiable collection, so you may want to wrap it with ArrayList (or other Collection class) to make it writable.