array

[sreelakshmi sarma]

Hi,
When i tried the following code i getting NullPointerException.
code:
class testarr {

public static void main(String[] args) {
char c[][]=new char[10][];
System.out.println(c[5]);
}
}
But when i changed the datatype to any other datatype like int,byte,long even String i am not getting any error. It's simply printing "null". Why is that?

[Tony Alicea]

I'm leaving that one to someone else. It doesn't make sense. I wonder what JDK 1.3 beta does...

[Jim Yingst]

jdk 1.3 beta does the exact same thing. The reason is that if you look at the API for PrintStream (which is what System.out is an instance of), you see:
<code><pre> public void println(char[] s)
public void println(Object obj)</pre></code>
There's no overload for any type of array besides char[] - any other array ends up invoking println(Object) instead. And it just happens that the authors of println(Object) thought to handle a NullPointerException by catching it themselves and printing the string "null", whereas the authors of println(char[]) didn't bother to catch a NullPointerException, though they probably should have.

[Tony Alicea]

Thanks Jim. I knew you would come up with he answer

[Arijit Ghosh]

I was going through old posts, and I found this interesting... I am having a similar doubt...

class abc{
 public static void main(String args[]){
  Integer[] a =  new Integer[2];
  System.out.println("a[0]->"+a[0]);
  Integer[][] b = new Integer[2][];
  System.out.println("b[0]->"+b[0]);
  System.out.println("b[0][0]->"+b[0][0]);
 }
}

Following is the output --
a[0]->null
b[0]->null
Exception in thread "main" java.lang.NullPointerException
at abc.main(abc.java:7)

Any explanation ??

[Barkat Mardhani]

Hi Jim:
Does 1.4 compiler also exibit same behavior? I do not have it yet...

[Barry Gaunt]

Java 1.4 gives same NullPointerException.
What we are discussing here is the behaviour
of System.out.println when it gets a null pointer to char[], right?
c[5] == null is correct.
So when we try to get at whatever c[5] is supposed to be referencing (a char[]) we are going through a null reference and so we get the NullPointerException.
Therefore I would say the behaviour is as expected.
-Barry

[Ron Newman]

If b[0] is null (which it is), then any reference to b[0][0] is going to cause a NullPointerException. That happens before System.out.println even gets called.