Question

I’m playing around with a GUI Sudoku solver that uses an array of JTextFields (gridArray) for display and an int array (sudokuGrid) for the actual solving. When I run it and it tries to cast the JTextField strings to ints, it throws a NumberFormatException on parsing the strings into ints, specifically this message:

java.lang.NumberFormatException: For input string: ""

Here’s the section of code that’s causing me trouble:

// create solveButton
    solveButton = new JButton("Solve It!");
    solveButton.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent arg0) {
            try {
                // create grid and call Solve()
                for(int i=0;i<9;i++) {
                    for(int j=0;j<9;j++) {
                        if (gridArray[i][j].getText() == "")
                            {sudokuGrid[i][j] = 0;}
                        else {sudokuGrid[i][j] = Integer.parseInt(gridArray[i][j].getText());}
                    }
                } // end for loop

                Solver(sudokuGrid);

                // display solution
                for(int i=0;i<9;i++) {
                    for(int j=0;j<9;j++) {
                        gridArray[i][j].setText(String.valueOf(sudokuGrid[i][j]));
                    }
                } // end for loop
            } catch (NumberFormatException e) {
                JOptionPane.showMessageDialog(mainFrame,e.toString(),"Number Format Exception",JOptionPane.ERROR_MESSAGE);
            } catch (Exception e) {
                JOptionPane.showMessageDialog(mainFrame,"Sorry, something broke, try again.","Solve Error",JOptionPane.ERROR_MESSAGE);
            } // end try-catch
        } // end actionPerformed()
    }); // end solveButton ActionListener

I thought that the if–else would catch the empty fields and only try the parseInt if there was a value present, but if anyone can enlighten me I’d appreciate it.

Answer 1

Your problem is here:

  if (gridArray[i][j].getText() == "")

You can’t compare strings that way. Do it this way instead:

if (gridArray[i][j].getText().equals(""))