Question

could someone explain to me why the following results in a Null pointer Exception? And how to set a value for bitarray[0]?

      BitSet[] bitarray;
      bitarray= new BitSet[10];
      bitarray[0].set(1);

Also, why something like this work and not result in a pointer exception?

     BitSet[] bitarray = new BitSet[10];
     BitSet bits = new BitSet(32);
     bits.set(1);
     bitarray[0] = bits;

Thanks

Answer 1

You can find nice help on Arrays Tutorial

In case of above example if you just declare array of 10 BitSet because defualt value of BitSet is null so it contains all null references

BitSet[] bitarray = new BitSet[10];

So initialize the reference you need to do

bitarray[index] =  new BitSet(SomeValue)