Important point regarding Autoboxing

[ankur rathi]

Conversions between primitives and wrapper classes now happen automatically
Drastically reduces the coding overhead
The compile inserts the extra code
Sorry, no null support

Got from the tutorial ...

please can any body explain me 4th point ???

thanks .

[Carol Enderlin]

Goes boom.

 
public class BoxExample
{
    public static void main( String[] args )
    {
        Integer i = null;
        int j = 0;
        j = j + i;
    }
}
 
C:\_Work\java\src>javac BoxExample.java
 
C:\_Work\java\src>java BoxExample
Exception in thread "main" java.lang.NullPointerException
        at BoxExample.main(BoxExample.java:7)
 
 

[ankur rathi]

Thanks a lot Carol .

we are getting NullPointerException because at the time of Auto Inboxing it internally calls intValue ( xxxValue ) & here everything goes wrong ..

Right ?

[Carol Enderlin]

There's always another question, eh?

Looks like it's calling intValue()

C:\_Work\java\src>javap -c BoxExample
Compiled from "BoxExample.java"
public class BoxExample extends java.lang.Object{
public BoxExample();
  Code:
   0:   aload_0
   1:   invokespecial   #1; //Method java/lang/Object."<init>" :( )V
   4:   return
 
public static void main(java.lang.String[]);
  Code:
   0:   aconst_null
   1:   astore_1
   2:   iconst_0
   3:   istore_2
   4:   iload_2
   5:   aload_1
   6:   invokevirtual   #2; //Method java/lang/Integer.intValue :( )I
   9:   iadd
   10:  istore_2
   11:  return
 
}
 
C:\_Work\java\src>
 

[ March 04, 2005: Message edited by: Carol Enderlin ]