Java object definition shorthand or shortcuts?

Question

Is there a faster way to instantiate objects in Java where one does not have to retype the class? For example, look at this tome of an instantiation:

HashMap<Integer, ArrayList<ActivityRecord>> days = new HashMap<Integer, ArrayList<ActivityRecord>>();

I'd love a shorthand that was along the lines of:

HashMap<Integer, ArrayList<ActivityRecord>> days = new();

Alternately, I'd also be happy with an Eclipse shortcut that auto-completed the instantiation to use the no-parameter constructor.

Answer 1

If you are using Java 7 and above you can use the diamond operator:

HashMap<Integer, ArrayList<ActivityRecord>> days = new HashMap<>();

Also, when declaring your variables it is good practice to use the interfaces when possible, instead of the concrete classes. So the above would really be:

Map<Integer, List<ActivityRecord>> days = new HashMap<>();

If you are using Java 6, you can do this using Google Guava:

Map<Integer, List<ActivityRecord>> days = Maps.newHashMap();

For further reading, you can check the section on Type Inference and Instantiation of Generic Classes in the Type Inference documentation.

Answer 2

You should the Java 7 diamond operator because often you'll be coding to the interface and not using the same class for the reference and the instance.

Map<Integer, ArrayList<ActivityRecord>> days = new HashMap<>();