尽管运行代码显示菜单，但Java applet显示白屏

Posted 2021-04-09

我有一个小游戏applet和朋友正在为我们的计算机科学课做准备。我们正在尝试创建一个在applet开头打开的菜单，然后在1秒后显示一个类选择屏幕。然而，在一秒钟之后，屏幕只是变成白色，但是输出分配的打印语句信号类选择屏幕已经加载，我不确定为什么会发生这种情况并且想要解决这个问题。

我已经尝试将代码放在另一个线程中显示类选择屏幕，因此在运行时没有别的东西会阻止它，但是，这没有改变。我还确保显示屏幕的条件是真实的，并且每隔0.2秒显示一次，但似乎没有任何效果。我试图让代码在角色的构造函数中运行，它应该运行一次，它运行一次，但运行一次的问题是它立即退出菜单并进入游戏的下一阶段没理由。

import java.awt.*;
import java.applet.*;
import java.awt.event.KeyListener;
import java.awt.event.KeyEvent;
import java.awt.event.*;
import java.io.*;
import javax.swing.*;
import java.util.*;

public class FinalProjectTest extends Applet implements KeyListener, Runnable, MouseListener
{
   int xCoord = 50;
   int yCoord = 600;
   int moveScale = 20;
   int xSize = 20;
   int ySize = 20;

   int leftWall = 0;
   int rightWall = 1000;
   int topWall = 0;
   int bottomWall = 650;
   public volatile Graphics graphics;
   boolean isInMenu = false;
   boolean firstRun = true;
   boolean drawMap = true;

   int hostileAmount = 1000;

   Character P1;

   @Override
   public void init()
   {
      addKeyListener(this);
      addMouseListener( this );
   }

   public void Looper(Graphics g)
   {
      drawPlayer(g);

      // Enemy 1
      HostileObject enemy = new HostileObject(100, 250);
      enemy.CreateHostile(g);
   }

   public void paint(Graphics g)
   {
      if (firstRun)
      {
         firstRun = false;
         isInMenu = true;
         System.out.println("Character Created");
         P1 = new Character(g);
      }
      if (!isInMenu && !firstRun)
      {
         System.out.println("Game has begun!");
         Map1 firstMap = new Map1(g);
         Looper(g);
      }
   }

   public void drawPlayer(Graphics g)
   {
      g.setColor(Util.black);
      g.fillRect(xCoord - xSize, yCoord - ySize, xSize, ySize);
   }

   public void MovePlayer(int x, int y)
   {
      if (CheckPosition(xCoord + x, yCoord + y))
      {
         xCoord += x;
         yCoord += y;
      }
   }

   public boolean CheckPosition(int x, int y)
   {
      if (WallCheck1(x,y) && WallCheck2(x,y) && CheckBorders(x, y))
      {
         return true;
      }
      else
         return false;
   }

   public boolean CheckBorders(int x, int y)
   {
      if (y + ySize <= bottomWall && y - ySize >= topWall && x - xSize >= leftWall && x + xSize <= rightWall)
      {
         return true;
      }
      else
         return false; 
   }

   public boolean WallCheck1(int x, int y)
   {
      if ((y - ySize >= Map1.wall1y1 || y + ySize <= Map1.wall1y2 + 20) || x - xSize >= Map1.wall1x2)
      {
         return true;
      }
      else
         return false; 
   }
   public boolean WallCheck2(int x, int y)
   {
      if ((y - ySize >= Map1.wall2y1 || y + ySize <= Map1.wall2y2 + 20) || x - xSize <= Map1.wall2x2)
      {
         return true;
      }
      else
         return false;
   }

   boolean keyIsHeld;
   char moveChar;

   public void keyReleased( KeyEvent e )
   {
      keyIsHeld = false;
      moveChar = ' ';
   }
   public void keyTyped( KeyEvent e ) { }

   public void keyPressed( KeyEvent a )
   {
      char c = a.getKeyChar();
      if ( c == 'w' )
      {
         moveChar = 'w';
         keyIsHeld = true;
      }
      else if ( c == 'a')
      {
         moveChar = 'a';
         keyIsHeld = true;
      }
      else if ( c == 's')
      {
         moveChar = 's';
         keyIsHeld = true;
      }
      else if ( c == 'd')
      {
         moveChar = 'd';
         keyIsHeld = true;
      }
   }

   public void mouseClicked(MouseEvent e)
   {
      int x = e.getX();
      int y = e.getY();
      if (isInMenu && P1.ClassID == 0)
      {
         if (x < 500 && y > 100 && y < 375)
         {
            P1.ClassID = 1;
            isInMenu = false;
            System.out.println(P1.Pseudo + " has chosen class: Warrior!");
         }
         if (x < 500 && y >= 375)
         {
            P1.ClassID = 3;
            isInMenu = false;
            System.out.println(P1.Pseudo + " has chosen class: UO3!");
         }
         if (x >= 500 && y > 100 && y < 375)
         {
            P1.ClassID = 2;
            isInMenu = false;
            System.out.println(P1.Pseudo + " has chosen class: Thief!");
         }
         if (x >= 500 && y >= 375)
         {
            P1.ClassID = 4;
            isInMenu = false;
            System.out.println(P1.Pseudo + " has chosen class: Mage!");
         }
         repaint();
      }
   }
   public void mouseEntered(MouseEvent e){}
   public void mouseExited(MouseEvent e) {}
   public void mousePressed(MouseEvent e) {}
   public void mouseReleased(MouseEvent e) {}
   public boolean mouseDown(Event e, int x, int y){return true;}

   public void run()
   {
      while (!isInMenu || !firstRun)
      {
         if (moveChar == 'w')
         {
            MovePlayer(0, -moveScale);
         }
         else if (moveChar == 'a')
         {
            MovePlayer(-moveScale, 0);
         }
         else if (moveChar == 's')
         {
            MovePlayer(0, moveScale);
         }
         else if (moveChar == 'd')
         {
            MovePlayer(moveScale, 0);
         }
         Util.wait(200);
         repaint();
      }
   } 

   Thread moveThread;
   Graphics g;
   boolean increaseDecrease = false;

   public void SetUpGraphics(Graphics graphics)
   {
      g = graphics;
   }

   public void start ()
   {
      if (moveThread == null)
      {
         moveThread = new Thread(this);
         moveThread.start();
      }
   }

}

class Map1 extends FinalProjectTest
{
   protected static int wall1x1 = 0;
   protected static int wall1y1 = 500;
   protected static int wall1x2 = 810;
   protected static int wall1y2 = 440;

   protected static int wall2x1 = 1000;
   protected static int wall2y1 = 200;
   protected static int wall2x2 = 190;
   protected static int wall2y2 = 140;
   public Map1(Graphics g)
   {
      Walls wall1 = new Walls(g, wall1x1, wall1y1, wall1x2, wall1y2);
      Walls wall2 = new Walls(g, wall2x1, wall2y1, wall2x2, wall2y2);
   }
}

class HostileObject
{
   private int startPosX, startPosY;
   private int xSize = 35;
   private int ySize = 35;
   public int health = 100;

   public HostileObject(int x, int y)
   {
      startPosX = x;
      startPosY = y;
   }

   public void CreateHostile(Graphics g)
   {
      g.setColor(Util.black);
      //Util.fillRect(g ,startPosX,startPosY,xSize,ySize);
   }
}

class Walls
{
   private static int wallCount = 2;

   public Walls(Graphics g, int x1, int y1, int x2, int y2)
   {
      Util.fillRect(g, x1, y1, x2, y2);
   }
}



class Character extends FinalProjectTest implements MouseListener, Runnable
{
   protected int ClassID = 0;
   protected int PlayerID = 0;
   protected int GP = 100;
   protected String Pseudo = "Muritor";
   protected boolean DebuggingMode = false;
   protected Graphics menuGraphics;
   Thread startMenuThread;

   public Character(Graphics g)
   {
      g.setColor(Util.black);
      Util.fillRect(g, 1, 1, 1000, 650);
      Util.drawButton(g, 1, 1, 1000, 100, "3 Floors", 2);
      Util.wait(1000);
      menuGraphics = g;
      startMenuThread = new Thread(this);
      startMenuThread.start();
   }

   public void run()
   {
      while (Thread.currentThread() == startMenuThread)
      {
         Util.fillRect(menuGraphics, 1, 1, 1000, 650);
         Util.drawButton(menuGraphics, 1, 1, 1000, 100, "Choose a Class", 2);
         Util.drawButton(menuGraphics, 1, 100, 500, 375, "Warrior", 1);
         Util.drawButton(menuGraphics, 501, 100, 1000, 375, "Thief", 1);
         Util.drawButton(menuGraphics, 1, 376, 500, 650, "UO3", 1);
         Util.drawButton(menuGraphics, 501, 376, 1000, 650, "Mage", 1);
         repaint();
         System.out.println("Menu loaded");
         Util.wait(200);
      }
   } 

   public static void ButtonSelection(Graphics g)
   {

   }
}



class Util
{
   static final Color black = Color.black;
   static final Color white = Color.white;

   public static void wait(int mil)
   {
      try
      {
         Thread.sleep((mil));
      }
      catch(InterruptedException ex)
      {
         Thread.currentThread().interrupt();
      }
   }

   public static void fillRect(Graphics g, int x1, int y1, int x2, int y2)
   {
      int widthPlaceholder = x2 - x1;
      int heightPlaceholder = y2 - y1;
      g.fillRect(x1,y1,widthPlaceholder,heightPlaceholder);
   }

   public static void drawButton(Graphics g, int x1, int y1, int x2, int y2, String title, int fontType)
   {
      g.setColor(Util.black);
      int widthPlaceholder = x2 - x1;
      int heightPlaceholder = y2 - y1;
      g.fillRect(x1,y1,widthPlaceholder,heightPlaceholder);
      g.setColor(Util.white);
      widthPlaceholder = x2 - x1;
      heightPlaceholder = y2 - y1;
      for (int k = 0; k < 3; k++)
      {
         g.drawRect(x1+k,y1+k,widthPlaceholder-k,heightPlaceholder-k);
      }
      switch(fontType)
      {
         case 1:
            Font characterCreateButton = new Font("SansSerif", Font.PLAIN, 75);
            g.setFont(characterCreateButton);
            g.drawString(title, x1+100, y1+100);
            break;
         case 2:
            Font characterCreateTitle = new Font("SansSerif", Font.BOLD, 100);
            g.setFont(characterCreateTitle);
            g.drawString(title, x1+25, y1+80);
            break;
         case 3:
            Font mainMenu = new Font("Arial", Font.ITALIC, 50);
            g.setFont(mainMenu);
            break;
      }
   }
}

我希望它每隔0.2秒说“菜单加载”并以相同的速率刷新实际的菜单屏幕，我收到消息，但小程序窗口只是白色。

答案

Problem #1

public class FinalProjectTest extends Applet implements KeyListener, Runnable, MouseListener {

我不了解你，但是当我编译你的代码时，我得到了

注意：... / FinalProjectTest.java使用或覆盖不推荐使用的API。注意：使用-Xlint重新编译：弃用以获取详细信息。

所以，如果我启用编译器标志，我得到......

Compiling 1 source file to .../build/classes
.../FinalProjectTest.java:18: warning: [deprecation] Applet in java.applet has been deprecated
public class FinalProjectTest extends Applet implements KeyListener, Runnable, MouseListener {
.../FinalProjectTest.java:179: warning: [deprecation] mouseDown(Event,int,int) in Component has been deprecated
    public boolean mouseDown(Event e, int x, int y) {
                   ^
.../FinalProjectTest.java:179: warning: [deprecation] Event in java.awt has been deprecated
    public boolean mouseDown(Event e, int x, int y) {
                             ^
3 warnings

这应该是警钟。

Applet已经被积极地弃用，并且不再受支持，并且相信已经在最新版本的API中删除了，认真的时间继续前进。

事实上，当我运行代码时，我得到：

警告：不推荐使用Applet API和AppletViewer。

Problem #2

public void paint(Graphics g) {
    if (firstRun) {
        firstRun = false;
        isInMenu = true;
        System.out.println("Character Created");
        P1 = new Character(g);
    }
    if (!isInMenu && !firstRun) {
        System.out.println("Game has begun!");
        Map1 firstMap = new Map1(g);
        Looper(g);
    }
}

绘画应该描绘状态，不做出合乎逻辑的决定或改变状态，事实上，更令人担忧的是......

P1 = new Character(g);

你永远不应该保持对你自己没有创建的Graphics上下文的引用。 AWT / Swing中的绘画系统使用共享上下文，因此所有组件将使用相同的Graphics上下文，也不能保证上下文在绘制周期之间是相同的。

这也强调了你不了解绘画系统在AWT / Swing中的工作原理。

从Performing Custom Painting和Painting in AWT and Swing开始，了解有关绘画实际如何工作以及如何使用它的更多细节

Problem ♾

好的，所以从那以后，其他所有事情都只是基于上面的复合，使情况变得更糟，例如......

    public void run() {
        while (Thread.currentThread() == startMenuThread) {
            Util.fillRect(menuGraphics, 1, 1, 1000, 650);
            Util.drawButton(menuGraphics, 1, 1, 1000, 100, "Choose a Class", 2);
            Util.drawButton(menuGraphics, 1, 100, 500, 375, "Warrior", 1);
            Util.drawButton(menuGraphics, 501, 100, 1000, 375, "Thief", 1);
            Util.drawButton(menuGraphics, 1, 376, 500, 650, "UO3", 1);
            Util.drawButton(menuGraphics, 501, 376, 1000, 650, "Mage", 1);
            repaint();
            System.out.println("Menu loaded");
            Util.wait(200);
        }
    }

这个“可能”似乎没问题，但是如果你理解了这幅画，你就会明白调用repaint会触发并画出传递并导致再次调用paint ......等等，坚持......

class Character extends FinalProjectTest implements MouseListener, Runnable {

为什么Character从FinalProjectTest延伸？它甚至没有添加到任何可以涂漆的容器中......亲爱的......

Answer...

重新开始。

不，严肃地说，扔掉你所做的并重新开始。这一次从阅读（和理解）开始......

• “责任分离”的基本OO设计概念。而不是将所有逻辑复合到一个方法中，将程序的每个部分的责任分成他们自己的类。菜单应该是一个独立的组件，游戏画布应该是它自己的，独立组件，你应该有一个“控制器”，根据这些组件的反馈（通过observer pattern）决定每个应该是什么时候显示（以及如何）。
• Model-View-Controller（渗入以前的评论）
• Performing Custom Painting和Painting in AWT and Swing
• How to Use Key Bindings因为KeyListener在这里不是一个好选择
• Concurrency in Swing因为Swing和大多数GUI框架一样，不是线程而且是单线程的，你应该知道如何处理它。
• How to Make Frames (Main Windows)因为Applet死了
• How to Use CardLayout因为这将有助于您的生活更轻松
• 使用JavaFX。至少你应该使用Swing，但如果可以的话，使用JavaFX