Try making the for loop as follows, otherwise, initialize the individual
elements of the checkerArray before sending in to the checkerRows. The
problem is you initialize the array. that is fine. But, you havenot
initialized the individual objects (for eg., checkerArray[0]) which you pass
in as parameter.

for(int f=0; f<checkerArray.length; f++)
{
checkerArray[f] = new TextField();
checkerRows.add(checkerArray[f]);
}