How to create a static Map of String -> Array

Question

I need to create a static Map which maps a given String to an array of int\'s.

In other words, I\'d like to define something l

Answer 1

You don't need to separate declaration and initialization. If you know how, it can all be done in one line!

// assumes your code declaring the constants ONE, FRED_TEXT etc is before this line
private static final Map myMap = Collections.unmodifiableMap(
    new HashMap() {{
        put(FRED_TEXT, new int[] {ONE, TWO, FOUR});
        put(DAVE_TEXT, new int[] {TWO, THREE});
    }});

What we have here is an anonymous class with an initialization block, which is a block of code that executes on construction after constructor, which we've used here to load the map.

This syntax/construct is sometimes erroneously called "double brace initialization" - I suppose because there's two adjacent braces - but there's actually no such thing.

The two cool things about this are:

• it marries the declaration with the contents, and
• because the initialization is in-line, you can also make an in-line call to Collections.unmodifiableMap(), resulting in a neat one-line declaration, initialization and conversion to unmodifiable.

If you don't need/want the map to be unmodifiable, leave out that call:

private static final Map myMap = new HashMap() {{
    put(FRED_TEXT, new int[] {ONE, TWO, FOUR});
    put(DAVE_TEXT, new int[] {TWO, THREE});
}};