Java for循环逻辑问题

Question

I am having trouble understanding why my for loop isn't behaving as I would like it. The purpose for my loop is to add multiple textfields onto a GUI, 70 to be exact. 7 across, 10 down. It adds the fields fine, but stops short one row and one column than I want. This seems to be enough information to identify the problem, but I can't, so I came here.

        for(int i = 0; i < 6; i++){
            for(int j = 0; j < 9; j++){
                OT2Field[i][j] = new JTextField();
                OT1Field[i][j] = new JTextField();
                STField[i][j] = new JTextField();
            }
        }

        int xPointer = 3;
        int yPointer = 7;
        for(int i = 0; i < 6; i++){
            for(int j = 0; j < 9; j++){
                addTimeFieldBorder0010(option3, OT2Field[i][j], gridbag, gbc, xPointer, yPointer, 1, 1, 0);
                yPointer = yPointer + 3;
            }
            xPointer++;
            yPointer = 7;
        }


    }

    private void addTimeFieldBorder0010(JComponent container, JComponent component, 
            GridBagLayout gridbag, GridBagConstraints gbc,
            int x, int y, int height, int width, double weightx) {
        gbc.gridx = x;
        gbc.gridy = y;
        gbc.gridheight = height;
        gbc.gridwidth = width;
        gbc.weightx = weightx;
        ((JTextField) component).setHorizontalAlignment(JLabel.CENTER);
        component.setBorder(BorderFactory.createMatteBorder(0, 0, 1, 0, Color.red));
        component.setFont(component.getFont().deriveFont(18.0f));
        component.setForeground(Color.red);
        component.setBackground(Color.YELLOW);
        gridbag.setConstraints(component, gbc);


        container.add(component, gbc);
     }

Answer 1

According to the Java Language Specification §15.20.1 ,

• The value produced by the < operator is true if the value of the left-hand operand is less than the value of the right-hand operand, and otherwise is false .

So you are starting at i = 0 and looping while i is less than 6. You need to loop while it is less than 7, or less than or equal to 6. The same applies to your next loop.

Change your two loops to:

for(int i = 0; i < 7; i++){
    for(int j = 0; j < 10; j++){
        //stuff
    }
}

Answer 2

Your outer loop only executes from 0 to 5 and inner loop only executes from 0 to 8. Change the loop to

for(int i = 0; i < 7; i++){
        for(int j = 0; j < 10; j++){
            OT2Field[i][j] = new JTextField();
            OT1Field[i][j] = new JTextField();
            STField[i][j] = new JTextField();
        }
    }

The < symbol return false when the value on the left is equal to right. So for i=6 , i<6 returns false and hence you are missing one iteration.

Answer 3

You're cycling between 0 to 5 for loop i and from 0 to 8 for loop j . That's why it stops short one row and one column. You should change them as follow:

for(int i = 0; i <= 6; i++){
  for(int j = 0; j <= 9; j++){
    ...
  }
}

or

for(int i = 0; i < 7; i++){
  for(int j = 0; j < 10; j++){
    ...
  }
}

Answer 4

for(int i = 0; i <= 6; i++){
    for(int j = 0; j <= 9; j++)

Answer 5

Your loop should be

for(int i = 0; i < 7; i++)
{
   for(int j = 0; j < 10; j++)
   {

       //your code
   }
}