I'm a student, and I've never tried declaring an array explicitly like this before. I want to put more than one sudoku grid into the class for the finished product, or else I would declare and initialize the array in one statement. I want for &quot;solved&quot; to refer to a different grid depending on whether an easy, medium or hard sudoku grid was selected. Is that possible? The way that I've written it results in a null pointer exception, but I am not sure how to declare an array as a class member and then initialize it explicitly within each constructor. If you could please straighten me out on syntax, I would appreciate it. I guess that something must be wrong with how I am declaring that array. This is what I used to test it: public class SudokuDriver {  public static void main(String[] args) {      SudokuSolution solved = new SudokuSolution();          System.out.println(solved.getSolved(0, 1));     System.out.println(solved.toString());  }}  And here is the class that I am testing: public class SudokuSolution { private int [][] solved;  public SudokuSolution () {          int [][] solved = {                  {6, 9, 7, 8, 3, 1, 4, 2, 5},                 {2, 8, 4, 9, 7, 5, 1, 6, 3},                 {5, 3, 1, 2, 6, 4, 9, 7, 8},                 {3, 4, 9, 1, 5, 6, 2, 8, 7},                 {7, 5, 8, 4, 9, 2, 3, 1, 6},                 {1, 6, 2, 7, 8, 3, 5, 9, 4},                 {4, 2, 6, 3, 1, 7, 8, 5, 9},                 {8, 1, 5, 6, 4, 9, 7, 3, 2},                 {9, 7, 3, 5, 2, 8, 6, 4, 1}             };     }      public int getSolved(int a, int b)  {                  return solved[a][b];                 }          public String toString()  {                  StringBuilder grid= new StringBuilder();         int i, j;                  for (i=0 ; i &lt; solved.length; i++) {             for (j = 0; j &lt; solved.length; j++)  {                 grid.append(solved [i][j] + ((i==solved.length - 1) ? &quot;\n&quot; : &quot; &quot;));             }         }                  return grid.toString();     }  }
What are Null Pointer Exceptions (java.lang.NullPointerException) and what causes them?  What methods/tools can be used to determine the cause so that you stop the exception from causing the program to terminate prematurely?
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