I use them very often, typically for creating and populating Map in one statement (rather than using an ugly static block):
private static final Map<String, String> CODES = new HashMap<String, String>() {
{
put("A", "Alpha");
put("B", "Bravo");
}
};
One interesting and useful embellishment to this is creating an unmodifiable map in one statement:
private static final Map<String, String> CODES =
Collections.unmodifiableMap(new HashMap<String, String>() {
{
put("A", "Alpha");
put("B", "Bravo");
}
});
Way neater than using static blocks and dealing with singular assignments to final etc.
And another tip: don’t be afraid to create methods too that simplify your instance block:
private static final Map<String, String> CODES = new HashMap<String, String>() {
{
put("Alpha");
put("Bravo");
}
void put(String code) {
put(code.substring(0, 1), code);
}
};