sampleArray[0]
has not been initialized as an array.
You initialized the first dimension of the array, but not the second one
You would need to do something like sampleArray[0] = new String[size]
The initializer String[][] sampleArray = new String[arrSize][]
works because you are creating an array that has references to other arrays. Each one of those other arrays can have a different size which you can set as you wish. What I mean is that the following would be perfectly legal:
sampleArray[0] = new String[10];
sampleArray[1] = new String[5];
System.out.println(sampleArray[0][9]);
System.out.println(sampleArray[1][4]);