Sonar complaining "The diamond operator ("<>") should be used"

Question

So I have below line of code in my file

List<String> nameList = new ArrayList<String>();

Now each time I run sonar scans it shows an error in above line saying I should use diamond operator instead. Now I understand that from Java7 compiler will automatically detect and supply the type of objects for ArrayList but my question is there a harm if I do it myself while declaring the class ?

Here is the rule link from Sonar website. I really don't understand the example they are supplying with this rule.

Is there any performance, efficiency or any other type of gain in changing the code to what Sonar is suggesting ?

Answer 1

Less you have helpless and duplicate code and more the code is readable and maintainable.

List<String> nameList = new ArrayList<String>();

or

List<String> nameList = new ArrayList<>();

Ok, not a lot of differences.

But suppose now that you have to change the generic: String by Integer, with the first way you have to do two modifications:

List<Integer> nameList = new ArrayList<Integer>();
      ^------               -------------^

Really not nice.

With the diamond a single one is required :

List<Integer> nameList = new ArrayList<>();
      ^---             

But take another example :

Map<String, List<Integer>> map = new HashMap<String, List<Integer>>();

or

Map<String, List<Integer>> map = new HashMap<>();

It makes things clearer.

In an application, you generally declare and instantiate tons of collections and generic classes. Refactoring it is really cheap. So just do it.