Java框架中的空白框架

Question

I have been trying to create a 10x10 grid in Java, and I tried to use the drawLines function in order to do so. However, when I run the program, all I see is a blank window with that will not close. These are my two classes to draw the grid. Could someone explain why this code does not work?

import java.awt.*;

public class RandomWalk extends Canvas{

    int width, height;

    public RandomWalk(int w, int h) {
        setSize(width = w, height = h);
    }

    public void paintGrid(Graphics g) {
        width = getWidth();
        height = getHeight();
        for(int i = 0; i < 11; i++) {
            g.drawLine(i*width/10, 0, i*width/10, height);
            g.drawLine(0, i*height/10, width, i*height/10);
        }
    }
}

import java.awt.*;

public class GridViewer extends Frame{

    GridViewer(String title, int w, int h) {
        setTitle(title);
        RandomWalk grid = new RandomWalk(w, h);
        add(grid);
    }

    public static void main(String[] args) {
        new GridViewer("Random Walk", 300, 300).setVisible(true);
    }
}

Answer 1

Add a printout to paintGrid like : System.out.println("paintGrid invoked");
Does it ever get invoked ?
This might help: Performing Custom Painting

Answer 2

You u need to override paint() method in Canvas class to achieve your goal and for the window closing, you need to add WindowListener to dispose the window (or u could simply use javax.swing.JFrame class instead of java.awt.Frame )

refer the below code

import java.awt.*;
import java.awt.event.*;

public class RandomWalk extends Canvas {

    int width, height;

    public RandomWalk(int w, int h) {
        setSize(width = w, height = h);
    }

    @Override
    public void paint(Graphics g) {
        width = getWidth();
        height = getHeight();
        for (int i = 0; i < 11; i++) {
            g.drawLine(i * width / 10, 0, i * width / 10, height);
            g.drawLine(0, i * height / 10, width, i * height / 10);
        }
    }
}

public class GridViewer extends Frame {

    GridViewer(String title, int w, int h) {
        setTitle(title);
        setSize(w, h);
        RandomWalk grid = new RandomWalk(w, h);
        add(grid);

        addWindowListener(new WindowAdapter() {
            @Override
            public void windowClosing(WindowEvent e) {
                dispose();
            }
        });
    }

    public static void main(String[] args) {
        new GridViewer("Random Walk", 300, 300).setVisible(true);
    }
}