Initialize List<> with Arrays.asList [duplicate]

Question

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String array initialization in Java [duplicate] (5 answers)

Closed 4 years ago.

Why does this work:

String[] array = {"a", "b", "c"};
List<String> list = Arrays.asList(array);

but this does not:

List<String> list = Arrays.asList({"a","b","c"});

Answer 1

This is a short hand only available when constructing and assigning an array.

String[] array = {"a", "b", "c"};

You can do this though:

List<String> list = Arrays.asList("a","b","c");

As asList can take "vararg" arguments.

Answer 2

Your question is why one works and the other does not, right?

Well, the reason is that {"a","b","c"} is not a valid Java expression, and therefore the compiler cannot accept it.

What you seem to imply with it is that you want to pass an array initializer without providing a full array creation expression (JLS 15.10).

The correct array creation expressions are, as others have pointed out:

String[] array = {"a", "b", "c"};

As stated in JLS 10.6 Array Initializers, or

String[] array = new String[]{"a", "b", "c"};

As stated in JLS 15.10 Array Creation Expressions.

This second one is useful for inlining, so you could pass it instead of an array variable directly.

Since the asList method in Arrays uses variable arguments, and variable arguments expressions are mapped to arrays, you could either pass an inline array as in:

List<String> list = Arrays.asList(new String[]{"a", "b", "c"});

Or simply pass the variable arguments that will be automatically mapped to an array:

List<String> list = Arrays.asList("a","b","c");

Answer 3

You can try

List<String> list = Arrays.asList(new String[] {"a","b","c"});