frog$ cat -n Test.java
     1 import java.util.*;
     2
     3 public class Test {
     4 public static void main(String[] args) {
     5 List<Test> l1 = new ArrayList<Test>();
     6 List<Test> l2 = (List<Test>)l1;
     7 }
     8 }
frog$ newjavac -gj Test.java
Test.java:6: interfaces java.util.List<Test> and java.util.List<Test> are incompatible; both define toArray(T[]), but with different return type
        List<Test> l2 = (List<Test>)l1;
                                    ^
1 error
frog$

=============

It doesn't seem to like to do == and != comparisons in some cases even
though both objects are of the same type. Here is an example:

import java.util.*;
public class Test{
     public static void main(String[] args){
         Map<Integer,Set<Integer>> map=new
HashMap<Integer,Set<Integer>>();
         map.put(new Integer(1),new HashSet<Integer>());
         map.put(new Integer(2),new HashSet<Integer>());
         if(map.get(new Integer(1))==map.get(new Integer(2))){
             System.err.println("equal");
         }else{
             System.err.println("not equal");
         }
     }
}


Here is the error produced:

Test.java:7: interfaces java.util.Set<java.lang.Integer> and
java.util.Set<java.lang.Integer> are incompatible; both define
toArray(T[]), but with different return type
         if(map.get(new Integer(1))==map.get(new Integer(2))){
                                   ^
1 error