Question

What is the difference between

 List list = new ArrayList<Integer>();

And

List<Integer> list = new ArrayList<Integer>();

Answer 1

By doing:

List list = new ArrayList<Integer>();

you are not telling the compiler what kind of List it is.
This would allow someone to compile this code:

String a =    (String)list.get(0);

which is clearly wrong and would cause you exception, because you can add anything in the list, so the compiler is not sure if list.get(0) is really an Integer.

Now with this way you are telling the compiler that this list will only accept and hold integers or Integer subclasses (in case it could be subclassed).

List<Integer> list = new ArrayList<Integer>();

so this wouldn’t compile:

String b = (String)list.get(0);