Null Pointer Exception

[Corbin Blake]

Can anybody tell me how i can get rid of a null pointer exception, that happens in a runtime error.

Here are all my variables for the entire class:

public Sequence[] seqArray = new Sequence[2];
public Sequence[] aStrand = new Sequence[20];
public Sequence test= new Sequence();
public int numSeq = 0;
public int testLength = 0;
public int number =0;
public int length = 0;
public Random generator = new Random();
public String[] gene ={"A","C","G","T"};
int d = 0;

here is my code

 
public Sequence[] randomSequence(int number, int length)  
{
    Random generator = new Random();
    test.sequence = null;
    for(int i = 0; i < number; i++){// number of sequences to be made
       aStrand[i].sequence = test.sequence; //<---here is where i get the nullpointer exception
        for(int j = 0; j < length; j++){//length of sequences to be made;
          int d = generator.nextInt(4);
          aStrand[i].sequence += gene[d];     
              }
          aStrand[i].sequence += gene[d];
          }
 
    return aStrand;   
       }
 

[Mike Gershman]

Based on the code you showed, you never put a reference to a Sequence object into aStrand[i], so you can't modify the instance variable "sequence" of a nonexistant object. In short, aStrand contains 20 references to null.
[ November 13, 2004: Message edited by: Mike Gershman ]

[Mike Gershman]

Try adding this after the declaration of aStrand:

 for ( int k = 0; k < aStrand.length; ++k )
    aStrand[ k ] = new Sequence();