Simple program but not getting class cast exception,why so?

[Vishal Hegde]

public class Box
{
   private Object object;

   public void add(Object object)
   {
      this.object=object;
   }

   public Object get()
   {
     return object;
    }
}

public class BoxDemo2
{
  public static void main(String []args)
  {
     Box IntegerBox=new Box();
     IntegerBox.add(new Integer("10")); // inputing string shouldnt this cause some error??
     Integer someinteger=(Integer)IntegerBox.get();  ////Why is this program not causing a class cast exception as trying to cast string into int
    System.out.println(someinteger);
  }
}

[Mohamed Sanaulla]

For passing "10" along with Integer constructor- As 10 string is parse able to integer its successful. You can try passing "ten" or some other string to get an ParseException.

The second query- Class cast exception- As the reference is actually an Integer, so casting it to Integer doesnt cause an exception. If it were some object of other class- say String you would get a classcast exception when you tried to cast.

Also before every cast- an instance of check is required so that you dont end up with ClassCastExceptions.

[Aditya Jha]

IntegerBox.add(new Integer("10"));

Think about it... what kind of object are you actually passing in IntegerBox.add method?

[Vishal Hegde]

Aditya Jha wrote:

IntegerBox.add(new Integer("10"));

Think about it... what kind of object are you actually passing in IntegerBox.add method?

it returns 10

[Matthew Brown]

Vishal Hegde wrote:

Aditya Jha wrote:

IntegerBox.add(new Integer("10"));

Think about it... what kind of object are you actually passing in IntegerBox.add method?

it returns 10

That's not quite what he's getting at. This is happening:
- You pass a String into an Integer constructor (check the API and you'll see this constructor exists)
- This results in an Integer object
- The Integer object is passed into the IntegerBox.add method
- Which means the object contained by IntegerBox is an Integer
- Which means the cast back to an Integer works fine