Java ArrayList and HashMap on-the-fly

Question

Can someone please provide an example of creating a Java ArrayList and HashMap on the fly? So instead of doing an add() or put()

Answer 1

Use a nice anonymous initializer:

List list = new ArrayList() {{
    add("a");
    add("b");
}};

Same goes for a Map:

Map map = new HashMap() {{
    put("a", "a");
    put("b", "b");
}};

I find this the most elegant and readable.

Other methods demand creating an array first, then converting it to a List - too expensive in my taste, and less readable.