Since Java 7 it’s not necessary to declare the type parameter twice while instantiating objects like Maps, Sets and Lists.
Consider the following code:
Map<String, List<String>> phoneBook = new HashMap<String, List<String>>();The type parameter for HashMap on the right-hand side of the expression seems redundant. This can be shortened using an empty “Diamond Operator” to give:
Map<String, List<String>> phoneBook = new HashMap<>();