Foo.java uses unchecked or unsafe operations. Note: Recompile with -Xlint:unchecked for details

Problem:

Note: Foo.java uses unchecked or unsafe operations. Note: Recompile with -Xlint:unchecked for detail

.

Solution  

This comes up in Java 5 and later if you're using collections without type specifiers (e.g., Arraylist() instead of ArrayList<String>()).

It means that the compiler can't check that you're using the collection in a type-safe way, using generics.

To get rid of the warning, just be specific about what type of objects you're storing in the collection. So, instead of using

List myList = new ArrayList();

use

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