array of Vectors - null pointer exception

[karl holmgren]

I am getting a null pointer exception for the last line of code, why? Am I not allowed to put Vector objects in arrays?

import java.util.*;

private int noCh=1;
private Vector channels[];
.
.
.
private channels = new Vector[noCh+1];
.
.
.
if(channels[ch].size()>=sample && sample>-1){.....}

Thanks!

[marc weber]

Originally posted by karl holmgren:
I am getting a null pointer exception for the last line of code, why? ...

I would need to see more of the code, but my guess is that channels[ch] is simply referencing a null value at some point (that is, there's no Vector object at the array index).
[ October 11, 2005: Message edited by: marc weber ]

[Ernest Friedman-Hill]

Hi Karl,

Welcome to JavaRanch!

You are indeed allowed to put Vectors into arrays. Java is complaining because you haven't done so! The line

private Vector channels = new Vector[noCh+1];

allocates an array of Vector variables -- i.e, references to Vectors. There are no Vectors in the array, though -- all those variables are null. You have to actually allocate the Vectors:

for (int k=0; k<channels.length; ++k)
  channels[k] = new Vector(); 

Then you can call size() on them.

If this is confusing you, have a look at this and this.
[ October 11, 2005: Message edited by: Ernest Friedman-Hill ]

[karl holmgren]

Thanks for the great answers!

When I fill the arrays with empty Vectors it works.