Java 图形更新/重绘图形

Question

I'm trying to work with the Java paint utility and it's been a bit of a hassle.

I'm trying to do something which I assume is quite basic. I'm drawing a square Graphic to a JPanel and then trying to move it using repaint

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

public class testGui {

   static gui      gc_gui;
   static int      gv_x;
   static int      gv_y;

   public static void main(String[] args) {

      gc_gui = new gui();
      gv_x = 50;
      gv_y = 50;

      gc_gui.cv_frame.setVisible(true);

   }

   public static class gui {

      JFrame    cv_frame;
      content   cv_content;

      public gui() {

         cv_frame = new JFrame();
         cv_frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
         cv_frame.setTitle("Test GUI");
         cv_frame.setSize(600, 400);
         cv_frame.setLayout(new FlowLayout());   

         cv_content = new content();
         cv_content.setBackground(Color.Black);
         cv_content.setPreferredSize(new Dimension(500, 300));
         cv_frame.add(cv_content);

         gv_x = 0;
         gv_y = 0;

         cv_content.update();

      }

   }

   public static class content extends JPanel {

      public void paint(Graphics graphic) {
         super.paint(graphic);
         draw(graphic);
      }

      public void update() {
         super.repaint();
      }

      public void draw(Graphics graphic) {
         Graphics2D graphic2D = (Graphics2D) graphic;
         graphic2D.setPaint(Color.Red);
         graphic2D.fillRect(gv_x, gv_y, 100, 100);
      }

   }

}

I don't know why the call to the update function isn't doing anything though.

It draws the square at 50x and 50y, the sets it to 0x and 0y immediately and then when I call repaint I expected it to be moved to it's new coordinates although it's still at 50x and 50y.

Why is this?

Answer 1

Your solution is to use KeyBindings.

https://docs.oracle.com/javase/tutorial/uiswing/misc/keybinding.html

and also. You need to create a Swing Timer, Thread, or Loop , that manages the frames to be painted. and such

Here is a link for Swing Timers as they are pretty easy to implement:

https://docs.oracle.com/javase/tutorial/uiswing/misc/timer.html

A lot of programs I see also have this ( AKA. working with threads.):

SwingUtilities.invokeLater(new Runnable() {
    public void run() {
        createAndShowGUI();
    }
});