Type safety issue

Question

Hi All,
Running the below code, works fine. but my expectation says the code in setobject method should throw Class CastException.
But this is not happening.
Is this a bug in jdk6. The type inintially defined as Integer afterwards converts into String.
public class Test<T> {
     private T value;
     public static void main(String[] args) {
          Test<Integer> test = new Test<Integer>();
          test.setObject("Test");
     private void setObject(Object obj) {
          try {
               value = (T)obj;
               System.out.println(value);
          } catch (ClassCastException castException) {
               castException.printStackTrace();
}

Answer 1

s_adi_bilaye wrote:
There is indeed a run-time type safety check at the cast operationIf there is an downcast from Object to the specific <T> in this case <Integer> then there needs to be an exception which is raised if there is a runtime type safety check.
When we dont use generics we get the runtime type safety check and a class cast exception is thrown.
Since no exception is raised at the cast line I understand that when we use generics there is no type safety check at the runtime for the "generic object". This explanation is also aligned with the generics documentation.
This is not quite correct. Your code would throw ClassCastExceptions due to compiler-generated casts if there were any.
You are declaring a List of Integers. Then you deliberately cheat the type-checks by using the "raw" type List to insert a String into the List.
So far, so good: no exception because of the cheating.
But after that, you never access the list's elements in a way that warrant a compiler-generated cast!
This line:
System.out.println(list.get(i));uses the overload PrintStream.println(Object).
Thus, the smart compiler decides that there is no need to first cast the list element to Integer and then immediately back to Object!
You can double-check by changing the line to:
System.out.println(list.get(i).intValue());Now the overload PrintStream.println(int) will be used, triggering the necessary cast to Integer, which will then throw a ClassCastException.