Generics

[Anup Om]

Hello,

I am studying generics.

Code Snippet#1

 List<Integer> l = new ArrayList(); //Warning
l.add("hello");//Compilation Error

Error Message:
cannot find symbol
symbol : method add(java.lang.String)
location: interface java.util.List<java.lang.Integer>
l.add("hello");
^

Code Snippet#2

  List l = new ArrayList<Integer>();
l.add("hello"); //Warning and runs without exception  

Code Snippet#1 flags a compilation error, while Code Snippet#2 compiles and runs. I fail to understand why and difference between the two declarations of the list l.

Thanks for help in advance.

[Henry Wong]

In the first case, you assigned an object that doesn't use generics to a reference that does -- hence the warning. Then you tried to add a string to a list that can only take integer (based on the reference) -- hence, the error.

In the second case, you assigned an object that uses generic to a reference that does not -- hence the warning. Then you tried to add a string to a list that doesn't use generics (based on the reference) -- which is perfectly fine.

Henry

[Anup Om]

Thank You. Now I am clear.