public ByteVector() 
{
      
        this(DEFAULT_BLOCK_SIZE);
}

 public ByteVector(int capacity) 
{
        if (capacity  > 0) {
            blockSize = capacity;
        } else {
            blockSize = DEFAULT_BLOCK_SIZE;
        }
        array = new byte[blockSize];
        n = 0;
}

 public ByteVector(byte[] a) 
{
        blockSize = DEFAULT_BLOCK_SIZE;
        array = a;
        n = 0;
}

 public ByteVector(byte[] a,
    int capacity) 
{
        if (capacity  > 0) {
            blockSize = capacity;
        } else {
            blockSize = DEFAULT_BLOCK_SIZE;
        }
        array = a;
        n = 0;
}

 public int alloc(int size) 
{
        int index = n;
        int len = array.length;
        if (n + size  >= len) {
            byte[] aux = new byte[len + blockSize];
            System.arraycopy(array, 0, aux, 0, len);
            array = aux;
        }
        n += size;
        return index;
}

This is to implement memory allocation in the array. Like malloc().

 public int capacity() 
{
        return array.length;
}

returns current capacity of array

 public byte get(int index) 
{
        return array[index];
}

 public byte[] getArray() 
{
        return array;
}

 public int length() 
{
        return n;
}

return number of items in array

 public  void put(int index,
    byte val) 
{
        array[index] = val;
}

 public  void trimToSize() 
{
        if (n <  array.length) {
            byte[] aux = new byte[n];
            System.arraycopy(array, 0, aux, 0, n);
            array = aux;
        }
}