Error from sudoku class

[Nattakan Lukkanapinit]

This is my code about SUDOKU
I got this error and don't know what it is.

Exception in thread "main" java.lang.NullPointerException
	at Sudoku.ForcedSet(test.java:265)
	at test.main(test.java:66)

  public class test
{
   public static void main(String[] args)
   {
      SudCell sud1, sud2, sud3;
      
      sud1 = new SudCell();
      sud2 = new SudCell();
      sud3 = new SudCell();

      if ( !sud1.ForcedSet(10) )
         System.out.print( "Bad 10\n" );

      if ( !sud2.ForcedSet(-1) )
         System.out.print( "Bad -1\n" );
      if ( !sud3.RuleOut(50) )
         System.out.print( "Bad 50\n" );

      System.out.print( "A: " + sud1.ToString() + "\n" );
      System.out.print( "B: " + sud2.ToString() + "\n" );
      System.out.print( "C: " + sud3.ToString() + "\n" );
      System.out.print( "\n" );

      System.out.print( "D: " + sud1.ToStringReveal() + "\n" );
      System.out.print( "E: " + sud2.ToStringReveal() + "\n" );
      System.out.print( "F: " + sud3.ToStringReveal() + "\n" );
      System.out.print( "\n" );

      sud1.ForcedSet(3);
      sud2.ForcedSet(9);
      sud3.RuleOut(0);
      sud3.RuleOut(2);
      sud3.RuleOut(4);
      sud3.RuleOut(6);
      sud3.RuleOut(8);
      
      System.out.print( sud1.ToString() + "\n" );
      System.out.print( sud2.ToString() + "\n" );
      System.out.print( sud3.ToString() + "\n" );
      System.out.print( "\n" );

      System.out.print( sud1.ToStringReveal() + "\n" );
      System.out.print( sud2.ToStringReveal() + "\n" );
      System.out.print( sud3.ToStringReveal() + "\n" );
      System.out.print( "\n" );

      sud1.Complete();
      sud2.Complete();
      sud3.Complete();

      System.out.print( sud1.IsCompleted() + " " + sud2.IsCompleted() + " "
         + sud3.IsCompleted() + "\n" );
      System.out.print( sud1.ValuePresent(1) + " " 
            + Boolean.toString(sud1.ValuePresent(2))
            + " " + Boolean.toString(sud1.ValuePresent(3)) + "\n" );
      System.out.print( Boolean.toString(sud3.ValuePresent(1)) 
            + " " + Boolean.toString(sud3.ValuePresent(2))
            + " " + Boolean.toString(sud3.ValuePresent(3)) + "\n" );
      
      
      Sudoku puzzle;

      puzzle = new Sudoku();
      
      // set some values in the matrix, attempting illegal
      puzzle.ForcedSet(3, 4, 5);
      puzzle.ForcedSet(7, 1, 3);
      puzzle.ForcedSet(9, 2, 6);
      for (int k = -1; k < 12; k++)
         if ( !puzzle.ForcedSet(k, k, k) )
            System.out.println( "Could not set " + k);

      System.out.print( "\n ------------- first basic ------------- \n");
      puzzle.Display(false);

      System.out.print( "\n ------------- then revealed ------------- \n");
      puzzle.Display(true);
      System.out.print( "\n" );;

      for (int row = Sudoku.MIN_VAL; row <= Sudoku.MAX_VAL ; row++)
         for (int col = Sudoku.MIN_VAL; col <= Sudoku.MAX_VAL ; col++)
         {
            // rule out 2 through 8 in all places except middle row and col
            if ( row == 5 || col == 5 )
               continue;
             for (int k = 2; k <= 8; k++)
               puzzle.RuleOut(row, col, k);
         }

      System.out.print( "\n ---------- after massive rule-outs ---------- \n");
      puzzle.Display(true);
   }
}

class Sudoku
{
   static final int MIN_VAL = SudCell.MIN_VAL;
   static final int MAX_VAL = 9;
   static final int NUM_VALS = 9;
   static final int SQRT_NUM_VALS = 3;
   static final int NOT_FINAL_YET = -1;
   
   SudCell suds[][] = new SudCell[NUM_VALS][NUM_VALS];
   
   public Sudoku()
   {
      
   }
   void Display(boolean reveal)
   {
      String output;
      int levlinecount = 0, sepcount = 0, divider = 0, divideend = 0;
      if (reveal == false)
      {
         for (int x=0;x<MAX_VAL;x++)
         {
            for (int y=0;y<MAX_VAL;y++)
            {
               output = suds[x][y].ToString();
               System.out.print(output);
               sepcount++;
               if (sepcount > 2)
               {
                  sepcount = 0;
                  if (levlinecount < 2)
                  {
                     System.out.print ("|");
                     levlinecount++;
                  }
                  else
                  {
                     levlinecount = 0;
                     if (divider < 2)
                     {
                        System.out.print( "\n" );
                        divider++;
                     }
                     else
                     {
                        if (divideend < 2)
                        {
                           System.out.print( "\n" + "---------------" +
                                 "--------------" +"\n" );
                           divider = 0;
                           divideend++;
                        }
                     }
                  }
               }
            }
         }
      }
      else
      {
         for (int x=0;x<MAX_VAL;x++)
         {
            for (int y=0;y<MAX_VAL;y++)
            {
               output = suds[x][y].ToStringReveal();
               System.out.print(output);
               sepcount++;
               if (sepcount > 2)
               {
                  sepcount = 0;
                  if (levlinecount < 2)
                  {
                     System.out.print ("|");
                     levlinecount++;
                  }
                  else
                  {
                     levlinecount = 0;
                     if (divider < 2)
                     {
                        System.out.print( "\n" );
                        divider++;
                     }
                     else
                     {
                        if (divideend < 2)
                        {
                           System.out.print( "\n" + "---------------" +
                                 "--------------" +"\n" );
                           divider = 0;
                           divideend++;
                        }
                     }
                  }
               }
            }
         }
      }
   }
   
   
   public int GetFinalValue(int row, int col)
   {
      return suds[row-1][col-1].GetFinalValue();
   }
   public boolean IsCompleted(int row, int col)
   {
      return suds[row-1][col-1].IsCompleted();
      
   }
   public boolean ValuePresent(int row, int col, int val)
   {
      return suds[row-1][col-1].ValuePresent(val);
   }
   public int NumRemainingVals(int row, int col)
   {
      return suds[row-1][col-1].NumRemainingVals();
   }
   public int NumRemainingValsTotal()
   {
      int total = 0;
      for (int x=0;x<MAX_VAL;x++)
      {
         for (int y=0;y<MAX_VAL;y++)
         {
            total += suds[x][y].GetFinalValue();
         }
      }
      return total;
   }
   public boolean AllSingletons()
   {
      boolean answer = true;
      for (int x=0;x<MAX_VAL;x++)
      {
         for (int y=0;y<MAX_VAL;y++)
         {
            if (NOT_FINAL_YET == suds[x][y].GetFinalValue())
               answer = false;
         }
      }
      return answer;
   }
   public boolean EmptyCellFound()
   {
      boolean answer = false;
      for (int x=0;x<MAX_VAL;x++)
      {
         for (int y=0;y<MAX_VAL;y++)
         {
            if (0 == suds[x][y].NumRemainingVals())
               answer = true;
         }
      }
      return answer;
   }
   
   public void SetToBlank()
   {
      for (int x=0;x<MAX_VAL;x++)
      {
         for (int y=0;y<MAX_VAL;y++)
         {
            suds[x][y].SetToBlank();
         }
      }
   }
   public boolean ForcedSet(int row, int col, int val)
   {
      return suds[row-1][col-1].ForcedSet(val);
   }
   public boolean Complete(int row, int col)
   {
      return suds[row-1][col-1].Complete();
   }
   public boolean RuleOut(int row, int col, int val)
   {
      return suds[row-1][col-1].RuleOut(val);
   }
   public boolean SoftSet(int row, int col, int val)
   {
      return suds[row-1][col-1].SoftSet(val);
   }
   
   boolean Validate(int val)
   {
      if (val < MIN_VAL || val > MAX_VAL)
         return false;
      else
         return true;
   }
   boolean  IndexValidate(int n)
   {
      if (n < 0 || n > NUM_VALS-1)
         return false;
      else
         return true;
   }
}

class SudCell
{
   private boolean digits[] = new boolean [9];
   private boolean completed;
   private int FinalValue;
   private int NumRemainingVals;
   private String String_Val,String_RVL;
   
   static final int MIN_VAL = 1;
   static final int MAX_VAL = 9;
   static final int NUM_VALS = 9;
   static final int SQRT_NUM_VALS = 3;
   static final int NOT_FINAL_YET = -1; 
   
   public SudCell()
   {
      for (int k=0;k<9;k++)
      {
         digits[k] = true;
      }
      completed = false;
   }

   public String ToString()
   {
      String output;
      int boolcount = 0;
      int whichdigit = 0;
      for (int x=0;x<9;x++)
      {
         if (digits[x] == true)
         {
            whichdigit = x;
            boolcount++;
         }
      }
      if (boolcount > 1 || boolcount < 1)
         output = " - ";
      else
      {
         whichdigit++;
         output = Integer.toString(whichdigit);
         output = " " + output + " ";
      }

      return output;
   }
   
   public String ToStringReveal()
   {
      String_RVL = "";
      if (digits[0] == true && digits[1] == false && digits[2] == false
            && digits[3] == false && digits[4] == false && digits[5] == false
            && digits[6] == false && digits[7] == false && digits[8] == false)
      {
         String_RVL = "1";
      }
      else if  (digits[0] == false && digits[1] == true && digits[2] == false
            && digits[3] == false && digits[4] == false && digits[5] == false
            && digits[6] == false && digits[7] == false && digits[8] == false)
      {
         String_RVL = "2";
      }
      else if  (digits[0] == false && digits[1] == false && digits[2] == true
            && digits[3] == false && digits[4] == false && digits[5] == false
            && digits[6] == false && digits[7] == false && digits[8] == false)
      {
         String_RVL = "3";
      }
      else if  (digits[0] == false && digits[1] == false && digits[2] == false
            && digits[3] == true && digits[4] == false && digits[5] == false
            && digits[6] == false && digits[7] == false && digits[8] == false)
      {
         String_RVL = "4";
      }
      else if  (digits[0] == false && digits[1] == false && digits[2] == false
            && digits[3] == false && digits[4] == true && digits[5] == false
            && digits[6] == false && digits[7] == false && digits[8] == false)
      {
         String_RVL = "5";
      }
      else if  (digits[0] == false && digits[1] == false && digits[2] == false
            && digits[3] == false && digits[4] == false && digits[5] == true
            && digits[6] == false && digits[7] == false && digits[8] == false)
      {
         String_RVL = "6";
      }
      else if  (digits[0] == false && digits[1] == false && digits[2] == false
            && digits[3] == false && digits[4] == false && digits[5] == false
            && digits[6] == true && digits[7] == false && digits[8] == false)
      {
         String_RVL =  "7";
      }
      else if  (digits[0] == false && digits[1] == false && digits[2] == false
            && digits[3] == false && digits[4] == false && digits[5] == false
            && digits[6] == false && digits[7] == true && digits[8] == false)
      {
         String_RVL = "8";
      }
      else if  (digits[0] == false && digits[1] == false && digits[2] == false
            && digits[3] == false && digits[4] == false && digits[5] == false
            && digits[6] == false && digits[7] == false && digits[8] == true)
      {
         String_RVL = "9";
      }
      else
      {
         for (int k=0;k<9;k++)
         {
            if (digits[0] = true)
               k=k+1;
            String_RVL = String_RVL +(k);
         }
      }
      return String_RVL = " "+String_RVL+" ";
   }

   public int GetFinalValue()
   {
      if (digits[0] == true && digits[1] == false && digits[2] == false
            && digits[3] == false && digits[4] == false && digits[5] == false
            && digits[6] == false && digits[7] == false && digits[8] == false)
      {
         FinalValue = 1;
      }
      else if  (digits[0] == false && digits[1] == true && digits[2] == false
            && digits[3] == false && digits[4] == false && digits[5] == false
            && digits[6] == false && digits[7] == false && digits[8] == false)
      {
         FinalValue = 2;
      }
      else if  (digits[0] == false && digits[1] == false && digits[2] == true
            && digits[3] == false && digits[4] == false && digits[5] == false
            && digits[6] == false && digits[7] == false && digits[8] == false)
      {
         FinalValue = 3;
      }
      else if  (digits[0] == false && digits[1] == false && digits[2] == false
            && digits[3] == true && digits[4] == false && digits[5] == false
            && digits[6] == false && digits[7] == false && digits[8] == false)
      {
         FinalValue = 4;
      }
      else if  (digits[0] == false && digits[1] == false && digits[2] == false
            && digits[3] == false && digits[4] == true && digits[5] == false
            && digits[6] == false && digits[7] == false && digits[8] == false)
      {
         FinalValue = 5;
      }
      else if  (digits[0] == false && digits[1] == false && digits[2] == false
            && digits[3] == false && digits[4] == false && digits[5] == true
            && digits[6] == false && digits[7] == false && digits[8] == false)
      {
         FinalValue = 6;
      }
      else if  (digits[0] == false && digits[1] == false && digits[2] == false
            && digits[3] == false && digits[4] == false && digits[5] == false
            && digits[6] == true && digits[7] == false && digits[8] == false)
      {
         FinalValue = 7;
      }
      else if  (digits[0] == false && digits[1] == false && digits[2] == false
            && digits[3] == false && digits[4] == false && digits[5] == false
            && digits[6] == false && digits[7] == true && digits[8] == false)
      {
         FinalValue = 8;
      }
      else if  (digits[0] == false && digits[1] == false && digits[2] == false
            && digits[3] == false && digits[4] == false && digits[5] == false
            && digits[6] == false && digits[7] == false && digits[8] == true)
      {
         FinalValue = 9;
      }
      else
         FinalValue = NOT_FINAL_YET;
      return FinalValue;
   }
   public boolean IsCompleted()
   {
      return completed;
   }
   public boolean ValuePresent(int val)
   {
      if (digits[val-1] == true)
         return true;
      else
         return false;
   }
   public int NumRemainingVals()
   {
      int boolcount = 0;
      for (int x=0;x<9;x++)
      {
         if (digits[x] == true)
            boolcount++;
      }
      return boolcount;
   }
   
   public void SetToBlank()
   {
      for (int x=0;x<9;x++)
      {
         digits[x] = true;
      }
   }
   
   public boolean ForcedSet(int val)
   {  
      if(val < MIN_VAL || val > MAX_VAL)
         return false;
      else
      {
      for (int x=0;x<9;x++)
      {
         digits[x] = false;
      }
      digits[val-1] = true;
      return true;
      }
   }
   public boolean Complete()
   {

      if (digits[0] == true && digits[1] == false && digits[2] == false
            && digits[3] == false && digits[4] == false && digits[5] == false
            && digits[6] == false && digits[7] == false && digits[8] == false)
      {
         completed = true;
         return true;
      }
      else if  (digits[0] == false && digits[1] == true && digits[2] == false
            && digits[3] == false && digits[4] == false && digits[5] == false
            && digits[6] == false && digits[7] == false && digits[8] == false)
      {
         completed = true;
         return true;
      }
      else if  (digits[0] == false && digits[1] == false && digits[2] == true
            && digits[3] == false && digits[4] == false && digits[5] == false
            && digits[6] == false && digits[7] == false && digits[8] == false)
      {
         completed = true;
         return true;
      }
      else if  (digits[0] == false && digits[1] == false && digits[2] == false
            && digits[3] == true && digits[4] == false && digits[5] == false
            && digits[6] == false && digits[7] == false && digits[8] == false)
      {
         completed = true;
         return true;
      }
      else if  (digits[0] == false && digits[1] == false && digits[2] == false
            && digits[3] == false && digits[4] == true && digits[5] == false
            && digits[6] == false && digits[7] == false && digits[8] == false)
      {
         completed = true;
         return true;
      }
      else if  (digits[0] == false && digits[1] == false && digits[2] == false
            && digits[3] == false && digits[4] == false && digits[5] == true
            && digits[6] == false && digits[7] == false && digits[8] == false)
      {
         completed = true;
         return true;
      }
      else if  (digits[0] == false && digits[1] == false && digits[2] == false
            && digits[3] == false && digits[4] == false && digits[5] == false
            && digits[6] == true && digits[7] == false && digits[8] == false)
      {
         completed = true;
         return true;
      }
      else if  (digits[0] == false && digits[1] == false && digits[2] == false
            && digits[3] == false && digits[4] == false && digits[5] == false
            && digits[6] == false && digits[7] == true && digits[8] == false)
      {
         completed = true;
         return true;
      }
      else if  (digits[0] == false && digits[1] == false && digits[2] == false
            && digits[3] == false && digits[4] == false && digits[5] == false
            && digits[6] == false && digits[7] == false && digits[8] == true)
      {
         completed = true;
         return true;
      }
      else
         return false;
   }
   public boolean RuleOut(int val)
   {
      if (val == 1)
      {
         digits[0] = false;
         return false;
      }
      else if (val == 2)
      {
         digits[1] = false;
         return false;
      }
      else if (val == 3)
      {
         digits[2] = false;
         return false;
      }
      else if (val == 4)
      {
         digits[3] = false;
         return false;
      }
      else if (val == 5)
      {
         digits[4] = false;
         return false;
      }
      else if (val == 6)
      {
         digits[5] = false;
         return false;
      }
      else if (val == 7)
      {
         digits[6] = false;
         return false;
      }
      else if (val == 8)
      {
         digits[7] = false;
         return false;
      }
      else if (val == 9)
      {
         digits[8] = false;
         return false;
      }
      else
      return false;
   }
   public boolean SoftSet(int val)
   {
      for (int k=0;k<9;k++)
      {
         for (int l=1;l<10;l++)
         {
            if (val == l)
            {
               digits[k] = true;
            }
         }
      }
      return false;
   }
   public boolean Validate(int val)
   {
      if (val >= MIN_VAL && val <= MAX_VAL)
      {
         return true;
      }
      else
         return false;
   }
}  

[Greg Charles]

When you initialize the suds array:

SudCell suds[][] = new SudCell[NUM_VALS][NUM_VALS];

that creates a two-dimensional array of nulls. That's an important point to remember with Java. When you try to work with one of those values, you instantly get a NullPointerException. You need to instantiate each element of the array using "new SudCell()" before you reference it.

[Nattakan Lukkanapinit]

Why i can't just call like this

    public Sudoku()
   {
      SetToBlank();
   }   

[Campbell Ritchie]

Never use == true or == false. Use if (xxx) or if (!xxx)

[Rob Spoor]

Hong hong wrote:Why i can't just call like this

    public Sudoku()
   {
      SetToBlank();
   }   

Because that calls suds[x][y].SetToBlank(); for each array element, but these are still all null as Greg said. In your constructor you need to add a block to initialize the array elements: suds[x][y] = new SudCell();

[pete stein]

cross-post: java-forums thread

[Rob Spoor]

Hong hong, please BeForthrightWhenCrosspostingToOtherSites.

[David Newton]

A few comments:

Java naming conventions: Standard Java naming conventions include starting method and variable names with a lower-case letter. Doing otherwise makes code more difficult to read than necessary.

Simplify logic expressions:

if (foo == true)
    return true;
else
    return false;

// Compare with

return foo;

Code organization: Put separate classes in separate files. To do otherwise obfuscates the logical separation of functionality, and makes navigation more difficult than necessary on both editing and cognitive levels.

Simplify flow: Consider your boolean RuleOut(int) method: first, every single path returns false. You only need one return, outside of any conditional. Second, pay attention to what you're doing: do you see any relationship between the val being passed in and the array index you're setting? This is a two-line method, unless the logic is completely wrong--which is possible, because a boolean method that always returns false doesn't need to return *anything*.

Particularly when trying to get help from people it's really important to keep things as simple, clear, and concise as possible. For your *own* benefit as well--code that's easy to read is easier to debug, understand, explain, extend, etc.

[David Newton]

You're going to get a lot more errors--you're trying to test things that are going to throw runtime exceptions.

Right now it seems to me like you wrote everything at once without running *anything* -- the main method isn't going to get passed the forcedSet(-1) line before crashing.

Start small. Test as you go. Look for ways to simplify what you're doing--don't just blindly throw code at a problem without taking the time to reflect on what you've just written. Be consistent in conventions. Localize functionality. Make sure you're not doing more work than necessary; simple example:

        System.out.print(sud1.valuePresent(1) + " "
                + Boolean.toString(sud1.valuePresent(2))
                + " " + Boolean.toString(sud1.valuePresent(3)) + "\n");

Here you're both not being consistent and doing more work than necessary--if the valuePresent(1) call is going to print correctly, why bother with the Boolean.toString(...) wrapping of the others? (And consider printf :)

I'm finding the code very difficult to follow as I bang on it, it's not clear to me what the intent of many things are. These things are fixable without a huge amount of effort.