Getting compiler error while using array constants in the constructor

Question

public class Sonnet29 implements Poem {
    private String[] poem;
    public Sonnet29() {
        poem = { "foo", "bar" , "baz"};
    }
    @Override
    public void recite() {
      //...
    }
}

Line poem = { "foo", "bar" , "baz"}; is giving compilation error.

Any specific reason why this is not allowed? How do I initialize a String array with array constants?

EDIT: Thank you folks for your answers. Now I'm clear what is allowed and what is NOT. But can I ask you why this is NOT allowed?

String[] pets;
pets = {"cat", "dog"};

After googling a bit, I found this link, where in, it is told that coding like this leaves the compiler in ambiguity - whether the pets should be array of Strings or array of Objects. However from the declaration, it can very well figure out that it is a String array, right???

If those are constants, then `poem` shouldn't be initialized in constructor. — True Soft, Jun 20 '10 at 06:57
@True Soft: I was just trying to 'initialize' the object state with some constants. Agree. If poem is declared as STATIC, private static String[] poem = { "foo", "bar" , "baz"}; it is working fine. — jai, Jun 20 '10 at 07:11
@HanuAthena, it doesn't matter whether the member is `static` or not, the problem here is that array initializer is allowed only in a declaration (§8.3, §9.3, §14.4), or as part of an array creation expression (§15.10). Therefore, without `static` it also will work `private String[] poem = { "foo", "bar" , "baz"};` if you do this on the spot — Andrew Tobilko, Aug 19 '16 at 07:29
Possible duplicate of [How to initialize an array in Java?](https://stackoverflow.com/questions/1938101/how-to-initialize-an-array-in-java) — Ivar, Aug 05 '19 at 09:19

score 65 · Accepted Answer · answered Jun 20 '10 at 06:57

65

This will do what you're looking for:

public Sonnet29() {
    poem = new String[] { "foo", "bar", "baz" };
}

Initialization lists are only allowed when creating a new instance of the array.

answered Jun 20 '10 at 06:57

ZoogieZork

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score 17 · Answer 2 · answered Jun 20 '10 at 08:24

From the Java language specification:

An array initializer may be specified in a declaration, or as part of an array creation expression (§15.10), creating an array and providing some initial values

In short, this is legal code:

private int[] values1 = new int[]{1,2,3,4};
private int[] values2 = {1,2,3,4}; // short form is allowed only (!) here

private String[][] map1 = new String[][]{{"1","one"},{"2","two"}};
private String[][] map2 = {{"1","one"},{"2","two"}}; // short form

List<String> list = Arrays.asList(new String[]{"cat","dog","mouse"});

and this is illegal:

private int[] values = new int[4];
values = {1,2,3,4}; // not an array initializer -> compile error

List<String> list = Arrays.asList({"cat","dog","mouse"}); // 'short' form not allowed

score 5 · Answer 3 · answered Jul 05 '10 at 19:08

{"cat", "dog"}

Is not an array, it is an array initializer.

new String[]{"cat", "dog"}

This can be seen as an array 'constructor' with two arguments. The short form is just there to reduce RSI.

They could have given real meaning to {"cat", "dog"}, so you could say things like

{"cat", "dog"}.length

But why should they make the compiler even harder to write, without adding anything useful? (ZoogieZork answer can be used easily)

Getting compiler error while using array constants in the constructor

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