JFrame油漆故障？

Question

所以这是我的代码：

package project;

import java.awt.Graphics;
import java.awt.event.KeyAdapter;
import java.awt.event.KeyEvent;

import javax.swing.JFrame;


public class Project extends JFrame {
String thing = "none";
int x = 100;
int y = 100; 
int w = 1600;
int h = 800;
int ww = 5;
int hh = 5;
public class AL extends KeyAdapter{
    public void keyPressed(KeyEvent e) {
        int KeyCode = e.getKeyCode();
        if (KeyCode == e.VK_NUMPAD1){
            downleft();
            if (thing == "none" || thing == "d" || thing == "dr" || thing == "l" || thing == "r" ||
                    thing == "ul" || thing == "u" || thing == "ur") {
                thing = "dl";
                System.out.println("Drawing down to the left!");
            }
        }
        if (KeyCode == e.VK_NUMPAD2){
            down();
            if (thing == "none" || thing == "dl" || thing == "dr" || thing == "l" || thing == "r" ||
                    thing == "ul" || thing == "u" || thing == "ur") {
                thing = "d";
            System.out.println("Drawing down!");
            }
        }
        if (KeyCode == e.VK_NUMPAD3){
            downright();
            if (thing == "none" || thing == "dl" || thing == "d" || thing == "l" || thing == "r" ||
                    thing == "ul" || thing == "u" || thing == "ur") {
                thing = "dr";
            System.out.println("Drawing down to the right!");
            }
        }
        if (KeyCode == e.VK_NUMPAD4){
            left();
            if (thing == "none" || thing == "dl" || thing == "d" || thing == "dr" || thing == "r" ||
                    thing == "ul" || thing == "u" || thing == "ur") {
                thing = "l";
            System.out.println("Drawing to the left");
            }
        }
        if (KeyCode == e.VK_NUMPAD6){
            right();
            if (thing == "none" || thing == "dl" || thing == "d" || thing == "dr" || thing == "l" ||
                    thing == "ul" || thing == "u" || thing == "ur") {
                thing = "r";
            System.out.println("Drawing to the right!");
            }
        }
        if (KeyCode == e.VK_NUMPAD7){
            upleft();
            if (thing == "none" || thing == "dl" || thing == "d" || thing == "dr" || thing == "l" ||
                    thing == "r" || thing == "u" || thing == "ur") {
                thing = "ul";
            System.out.println("Drawing up to the left!");
            }
        }
        if (KeyCode == e.VK_NUMPAD8){
            up();
            if (thing == "none" || thing == "dl" || thing == "d" || thing == "dr" || thing == "l" ||
                    thing == "r" || thing == "ul" || thing == "ur") {
                thing = "u";
            System.out.println("Drawing up!");
            }
        }
        if (KeyCode == e.VK_NUMPAD9){
            upright();
            if (thing == "none" || thing == "dl" || thing == "d" || thing == "dr" || thing == "l" ||
                    thing == "r" || thing == "ul" || thing == "u") {
                thing = "ur";
            System.out.println("Drawing up to the right!");
            }
        }
        if (KeyCode == e.VK_B){
            ww += 5;
            hh += 5;
            System.out.println("Resized! It is now " + ww + " by " + hh + "!");
            if (ww > 150) {
                ww = 150;
                hh = 150;
                System.out.println("The size went too high! Resized back to 150 by 150!");
            }
        }
        if (KeyCode == e.VK_S){
            ww -= 5;
            hh -= 5;
            System.out.println("Resized! It is now " + ww + " by " + hh + "!");
            if (ww < 5) {
                ww = 5;
                hh = 5;
                System.out.println("The size went too low! Resized back to 5 by 5!");
            }
        }
    }
}
public void downleft(){
    x-=5;
    y+=5;
}
public void down(){
    y+=5;
}
public void downright(){
    x+=5;
    y+=5;
}
public void left(){
    x-=5;
}
public void right(){
    x+=5;
}
public void upleft(){
    x-=5;
    y-=5;
}
public void up(){
    y-=5;
}
public void upright(){
    x+=5;
    y-=5;
}
public Project(){
    addKeyListener(new AL());
    setTitle("Escher Sketch");
    setResizable(false);
    setVisible(true);
    setSize(w, h);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
public void paint(Graphics g) {
    g.fillRect(x, y, ww, hh);
    repaint();
}
public static void main(String[] args) {
    new Project();
}
}

出于某种原因，当我跑它时，它只是一个黑色的窗口，左上角有一个小的白色矩形。我多次阅读代码，看起来它应该可以工作。它正在我的另一台计算机上工作，然后我尝试将该文件放在这台计算机上，但它没有。如果有人能帮助我那会很棒。

Answer 1

将您的代码从Project()部分更改为：

public Project(){
    addKeyListener(new AL());
    setTitle("Escher Sketch");
    setResizable(false);
    setVisible(true);
    setSize(w, h);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    getContentPane().add(new MyGraphics());
}
public static void main(String[] args) {
    new Project();
}
class MyGraphics extends JPanel {
    public void paintComponent(Graphics g) {
        g.fillRect(x, y, ww, hh);
        repaint();
    }
}
}

Answer 2

为什么你不使用Panel而不是将绘画应用到JFrame本身

这里有一些参考：

JFrame, JPanel, paintComponent how to

http://www.java2s.com/Code/JavaAPI/javax.swing/JPanelpaintComponentGraphicsg.htm

请注意，如果要刷新面板调用repaint();