Double Initialization pattern in Java

Java does not have a convenient literal syntax for creating lists or maps. However a neat hack called the Double Initialization pattern allows you to get close to this.

Set<String> names = new HashSet<String>() { {
    add("Siddharth");
    add("Vedant");
} };

The outer set of braces creates a new Anonymous Inner class. And the second inner set of braces is a initializer block that runs when the instance is created.

The pattern is close enough to a literal list (or map) that is initialized with some values.