JFrame not displaying Canvas

Question

I've recently been working with BufferStrategy and JFrame for preliminary graphics. However, when attempting to draw a simple rectangle to the frame, nothing appears. Here is the code:

import java.awt.*;
import java.awt.image.BufferStrategy;
import javax.swing.*;

public class GTestingMain {

public static void main(String[] args) {

    JFrame myFrame = new JFrame();
    Canvas myCanvas = new Canvas();
    Graphics2D g;
    BufferStrategy strategy;

    myFrame.setSize(500, 500);
    myFrame.setResizable(false);
    myFrame.setLocationRelativeTo(null);
    myFrame.setVisible(true);
    myFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    myCanvas.setPreferredSize(new Dimension(500, 500));

    myFrame.add(myCanvas);
    myFrame.pack();

    strategy = myCanvas.getBufferStrategy();
    if(strategy == null) {
        myCanvas.createBufferStrategy(3);
    }
    strategy = myCanvas.getBufferStrategy();//Throwing in again so strategy != null

    do {

        do {

            g = (Graphics2D) strategy.getDrawGraphics();
            g.setColor(Color.WHITE);
            g.fillRect(0, 0, 500, 500);
            g.setColor(Color.red);
            g.fillRect(10, 40, 50, 70);
            g.dispose();


        }while(strategy.contentsRestored());
        strategy.show();

    }while(strategy.contentsLost());

}

}

Now the problem is a little more unique. When I go into the debugger and step through the code, it works just fine. If I run normally, blank. If I click on the Frame before it is drawn to while in the debugger - blank.

I know I can 'solve' this issue with a thread, but i'd like to know why it works* in debug mode but not in a regular run. Thanks!

Answer 1

Before you start off with bufferStrategies, go through java doc

It says that,

A buffer strategy gives you two all-purpose methods for drawing: getDrawGraphics and show. When you want to start drawing, get a draw graphics and use it. When you are finished drawing and want to present your information to the screen, call show. These two methods are designed to fit rather gracefully into a rendering loop:

What you are missing is a rendering loop basically. Also since it uses volatile images for its buffer, we never know when our video memory is lost. That explains why you were getting the rectangle in debug mode. Its like a callback system with contentLost and contentsRestored methods.

Just wrap your do while loops as below.

while(isHappy()){ // your logic goes here.
    do {

        do {

            g = (Graphics2D) strategy.getDrawGraphics();
            g.setColor(Color.WHITE);
            g.fillRect(0, 0, 500, 500);
            g.setColor(Color.red);
            g.fillRect(10, 40, 50, 70);
            g.dispose();


        }while(strategy.contentsRestored());
        strategy.show();

    }while(strategy.contentsLost());
}