Thread: Trouble with draw and fillRect in pyramid logic using nested loop

Hello eveyone. I'm working on a project for a class to build a pyramid out of bricks using a user entered height in bricks between 1 and 100. I'm using a nested loop to draw a row of bricks then move up the height of a brick and draw the next row ect. The problem is when I enter the height of the pyramid and hit the button the first time nothing happens. When I hit the button a second time it only draws the first row of bricks. I spent a few hours writing the code and figuring out the logic and a couple of days trying to debug it. The code displays some diagnostic message dialogs that show the values of the variables before they enter the inner loop. The loops seem to be working and the variables are what I expected them to be. I even created a seperate method to draw the bricks that is called from the inner loop. Please take a look and let me know what I did wrong. I could really use a fresh pair of eyes. Also, is there a way to clear the panel before hitting the start button? Sorry about all the commented lines but I'm using them to turn off the statements when I rewrite the code. Thanks so much for you help.

]import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
 
public class Pyramid extends JFrame implements ActionListener
    {
 
    private JPanel panel;
//    private Random random;
    private JTextField pyramidHeightField;
    private JLabel pyramidHeightLabel;
    private JButton buildPyramidButton;
 
    public static void main (String[] args)
    {
        Pyramid frame = new Pyramid();
        frame.setSize(400, 500);
        frame.setTitle("Pyramid");
        frame.createGUI();
        frame.setVisible(true);
    }
 
    private void createGUI()
    {
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        Container window = getContentPane();
        window.setLayout(new FlowLayout() );
 
        panel = new JPanel();
        panel.setPreferredSize(new Dimension(400, 400));
        panel.setBackground(Color.white);
        window.add(panel);
 
        pyramidHeightLabel = new JLabel("Enter Pyramid height from 1 to 100  ");
        window.add(pyramidHeightLabel);
        pyramidHeightField = new JTextField(10);
        window.add(pyramidHeightField);
 
        buildPyramidButton = new JButton("Build Pyramid");
        window.add(buildPyramidButton);
        buildPyramidButton.addActionListener(this);
    }
 
    public void actionPerformed(ActionEvent event)
    {
        int pyramidHeight, brickSize, random;
        int x = 0, y = 400, hLoop = 1, vLoop = 1, endWhile = 0;
        String diagText1, diagText2, diagText3, diagString;
 
        pyramidHeight = Integer.parseInt(pyramidHeightField.getText());
        if (pyramidHeight < 1 || pyramidHeight > 100)
        {
            pyramidHeight = 50;
        }
        brickSize = 400 / pyramidHeight;
 
 
        Graphics paper = panel.getGraphics();
 
        for (vLoop = 1; vLoop <= pyramidHeight; vLoop++)
        {
            y = y - brickSize;
 
            diagText1 = (Integer.toString(vLoop));
            diagText2 = (Integer.toString(x));
            diagText3 = (Integer.toString(y));
 
            endWhile = ((pyramidHeight + 1) - vLoop);
 
            while (hLoop <= endWhile)
            {
//                paper.setColor(Color.yellow);
//                paper.fillRect(x, y, brickSize, brickSize);
                drawBrick(paper, x, y, brickSize);
 
//                paper.setColor(Color.black);
//                paper.drawRect(x, y, brickSize, brickSize);
 
 
                x += brickSize;
 
                hLoop++;
            }
//            diagText1 = (Integer.toString(vLoop));
//            diagText2 = (Integer.toString(x));
//            diagText3 = (Integer.toString(y));
 
            x = (brickSize / 2) * vLoop;
 
            JOptionPane.showMessageDialog (null,
            diagString = "vLoop = " + diagText1 + " x = " + diagText2 + " y = " + diagText3);
 
 
        }
 
    }
    private void drawBrick(Graphics drawingArea, int xPos, int yPos, int size)
    {
        drawingArea.setColor(Color.yellow);
        drawingArea.fillRect(xPos, yPos, size, size);
        drawingArea.setColor(Color.black);
        drawingArea.drawRect(xPos, yPos, size, size);
    }   
 
 
}

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
 
public class Pyramid extends JFrame implements ActionListener
    {
 
    private JPanel panel;
//    private Random random;
    private JTextField pyramidHeightField;
    private JLabel pyramidHeightLabel;
    private JButton buildPyramidButton;
 
    public static void main (String[] args)
    {
        Pyramid frame = new Pyramid();
        frame.setSize(400, 500);
        frame.setTitle("Pyramid");
        frame.createGUI();
        frame.setVisible(true);
    }
 
    private void createGUI()
    {
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        Container window = getContentPane();
        window.setLayout(new FlowLayout() );
 
        panel = new JPanel();
        panel.setPreferredSize(new Dimension(400, 400));
        panel.setBackground(Color.white);
        window.add(panel);
 
        pyramidHeightLabel = new JLabel("Enter Pyramid height from 1 to 100  ");
        window.add(pyramidHeightLabel);
        pyramidHeightField = new JTextField(10);
        window.add(pyramidHeightField);
 
        buildPyramidButton = new JButton("Build Pyramid");
        window.add(buildPyramidButton);
        buildPyramidButton.addActionListener(this);
    }
 
    public void actionPerformed(ActionEvent event)
    {
        int pyramidHeight, brickSize, random;
        int x = 0, y = 400, hLoop = 1, vLoop = 1, endWhile = 0;
        String diagText1, diagText2, diagText3, diagString;
 
        pyramidHeight = Integer.parseInt(pyramidHeightField.getText());
        if (pyramidHeight < 1 || pyramidHeight > 100)
        {
            pyramidHeight = 50;
        }
        brickSize = 400 / pyramidHeight;
 
 
        Graphics paper = panel.getGraphics();
 
        for (vLoop = 1; vLoop <= pyramidHeight; vLoop++)
        {
            y = y - brickSize;
 
            diagText1 = (Integer.toString(vLoop));
            diagText2 = (Integer.toString(x));
            diagText3 = (Integer.toString(y));
 
            endWhile = ((pyramidHeight + 1) - vLoop);
 
            while (hLoop <= endWhile)
            {
//                paper.setColor(Color.yellow);
//                paper.fillRect(x, y, brickSize, brickSize);
                drawBrick(paper, x, y, brickSize);
 
//                paper.setColor(Color.black);
//                paper.drawRect(x, y, brickSize, brickSize);
 
 
                x += brickSize;
 
                hLoop++;
            }
 
//*************************
            hLoop = 1;
//*************************
 
 
//            diagText1 = (Integer.toString(vLoop));
//            diagText2 = (Integer.toString(x));
//            diagText3 = (Integer.toString(y));
 
            x = (brickSize / 2) * vLoop;
 
            JOptionPane.showMessageDialog (null,
            diagString = "vLoop = " + diagText1 + " x = " + diagText2 + " y = " + diagText3);
 
 
        }
 
    }
    private void drawBrick(Graphics drawingArea, int xPos, int yPos, int size)
    {
        drawingArea.setColor(Color.yellow);
        drawingArea.fillRect(xPos, yPos, size, size);
        drawingArea.setColor(Color.black);
        drawingArea.drawRect(xPos, yPos, size, size);
    }   
 
 
}

I change, I reset hLoop back to 1 .

You can use Graphics.clearRect( ) with it's params to clear the area

Chris

Thanks so much for your help Chris. I forgot to reinitalize hLoop...silly me. Do you know why the program won't draw the first time you hit the button? I've seen it happen on other programs I've written. Is this a common problem? Also is there way to clear the whole panel rather and clearing each Rect?

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
 
public class Pyramid extends JFrame implements ActionListener
    {
 
    private JPanel panel;
//    private Random random;
    private JTextField pyramidHeightField;
    private JLabel pyramidHeightLabel;
    private JButton buildPyramidButton;
 
    public static void main (String[] args)
    {
        Pyramid frame = new Pyramid();
        frame.setSize(400, 500);
        frame.setTitle("Pyramid");
        frame.createGUI();
        frame.setVisible(true);
    }
 
    private void createGUI()
    {
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        Container window = getContentPane();
        window.setLayout(new FlowLayout() );
 
        panel = new JPanel();
        panel.setPreferredSize(new Dimension(400, 400));
        panel.setBackground(Color.white);
        window.add(panel);
 
        pyramidHeightLabel = new JLabel("Enter Pyramid height from 1 to 100  ");
        window.add(pyramidHeightLabel);
        pyramidHeightField = new JTextField(10);
        window.add(pyramidHeightField);
 
        buildPyramidButton = new JButton("Build Pyramid");
        window.add(buildPyramidButton);
        buildPyramidButton.addActionListener(this);
    }
 
    public void actionPerformed(ActionEvent event)
    {
        int pyramidHeight, brickSize, random;
        int x = 0, y = 400, hLoop = 1, vLoop = 1, endWhile = 0;
        String diagText1, diagText2, diagText3, diagString;
 
        pyramidHeight = Integer.parseInt(pyramidHeightField.getText());
        if (pyramidHeight < 1 || pyramidHeight > 100)
        {
            pyramidHeight = 50;
        }
        brickSize = 400 / pyramidHeight;
 
 
        Graphics paper = panel.getGraphics();
 
//*********************************
        paper.clearRect(0,0,400,400);        
//*********************************
 
        for (vLoop = 1; vLoop <= pyramidHeight; vLoop++)
        {
            y = y - brickSize;
 
            diagText1 = (Integer.toString(vLoop));
            diagText2 = (Integer.toString(x));
            diagText3 = (Integer.toString(y));
 
            endWhile = ((pyramidHeight + 1) - vLoop);
 
            while (hLoop <= endWhile)
            {
//                paper.setColor(Color.yellow);
//                paper.fillRect(x, y, brickSize, brickSize);
                drawBrick(paper, x, y, brickSize);
 
//                paper.setColor(Color.black);
//                paper.drawRect(x, y, brickSize, brickSize);
 
 
                x += brickSize;
 
                hLoop++;
            }
 
 
            hLoop = 1;
 
 
 
//            diagText1 = (Integer.toString(vLoop));
//            diagText2 = (Integer.toString(x));
//            diagText3 = (Integer.toString(y));
 
            x = (brickSize / 2) * vLoop;
 
            JOptionPane.showMessageDialog (null,
            diagString = "vLoop = " + diagText1 + " x = " + diagText2 + " y = " + diagText3);
 
 
        }
 
    }
    private void drawBrick(Graphics drawingArea, int xPos, int yPos, int size)
    {
        drawingArea.setColor(Color.yellow);
        drawingArea.fillRect(xPos, yPos, size, size);
        drawingArea.setColor(Color.black);
        drawingArea.drawRect(xPos, yPos, size, size);
    }   
 
 
}

that clears it all at once. it works on first press for me :/

Chris