Question

In C# you can initialize Hashtables (and many other types of objects) using code like this –

Hashtable table = new Hashtable {{1, 1}, {2, 2}};

Is there anything like this in Java or do you have to just declare the Hashtable first and then manually put items in it one by one?

Answer 1

This is answered elsewhere but you can use an anonymous subclass:

new HashMap<Integer, Integer>() {{ put(1, 1); put(2, 2); }};

Lot’s of boiler plate, but still a one-liner :). This will, unfortunately, also complain about the missing serialVersionUID constant which you can either add or ignore the warning on.

This is called an instance initializer block, more information here.