Funnily enough, your code won't compile. The generic signature of your hash map is incompatible with the signature of your variable declaration. You'll instead

Funnily enough, your code won't compile. The generic signature of your hash map is incompatible with the signature of your variable declaration. You'll instead get a verbose error message like the following: Test.java:6: incompatible types found : java.util.HashMap<java.lang.String,java.util.ArrayList<java.lang.String>> required: java.util.Map<java.lang.String,java.util.List<java.lang.String>> Map<String, List<String>> buf = new HashMap<String, ArrayList<String>>(); There really are productivity wins to using some of these newer languages, but you'll never learn that by just whining about their existence.