我一直在研究我的项目，但很难知道我可以解决什么问题，以便让它发挥作用，我是一个初学者，只是想让你知道..
这是错误消息:
Exception in thread "AWT-EventQueue-1" java.lang.NullPointerException: String is null
at sun.java2d.SunGraphics2D.drawString(SunGraphics2D.java:2817)
at project2.project2.paint(project2.java:101)
at sun.awt.RepaintArea.paintComponent(RepaintArea.java:264)
at sun.awt.RepaintArea.paint(RepaintArea.java:240)
at sun.awt.windows.WComponentPeer.handleEvent(WComponentPeer.java:347)
at java.awt.Component.dispatchEventImpl(Component.java:4937)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:729)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:688)
at java.awt.EventQueue$3.run(EventQueue.java:686)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.awt.EventQueue$4.run(EventQueue.java:702)
at java.awt.EventQueue$4.run(EventQueue.java:700)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:699)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)
这是我的代码:
package project2;
import java.awt.*;
import java.applet.*;
public class project2 extends Applet
{
Image tortoise, hare;
int tortX = 250, hareX = 250;
final int tortY = 100, hareY = 300, WIDTH = 15, HEIGHT = 50;
int turn; String turnNum;
int move; String tMove, hMove;
public void init()
{
tortoise = getImage( getDocumentBase(), "images/tortoise.gif" );
hare = getImage( getDocumentBase(), "images/hare.gif" );
move = 0; turn = 0;
}
public void control()
{
while (( tortX < 985 ) || ( hareX < 985 ))
{
move = (int)(10 * Math.random());
switch (move)
{
case 1:
case 2:
tortX += (3 * WIDTH);
hareX += (9 * WIDTH);
tMove = "Fast Plod"; hMove = "Big Hop";
break;
case 3:
case 4:
case 5:
tortX += (3 * WIDTH);
hareX += WIDTH;
tMove = "Fast Plod"; hMove = "Small Hop";
break;
case 6:
tortX += WIDTH;
if (hareX == 250) {} // Agit Nihil
else if (hareX <= (250 + (11 * WIDTH)))
hareX = 250;
else
hareX -= (12 * WIDTH);
tMove = "Slow Plod"; hMove = "Big Slip";
break;
case 7:
case 8:
tortX += (1 * WIDTH);
if (hareX == 250) {} // Agit Nihil
else if (hareX <= (250 + (WIDTH)))
hareX = 250;
else
hareX -= (2 * WIDTH);
tMove = "Slow Plod"; hMove = "Small Slip";
break;
case 9:
case 10:
if (tortX == 250) {} // Agit nihil
else if (tortX <= (250 + (5 * WIDTH)))
tortX = 250;
else
tortX -= (6 * WIDTH);
tMove = "Slip"; hMove = "Fall Asleep.";
break;
// Cuniculus dormit, agit nihil .
}
turn++; turnNum = (turn + "");
repaint();
for (int i = 1; i <= 10; i++)
{
delay();
}
}
tortX = 985; hareX = 985;
repaint();
}
public void paint( Graphics screen )
{
drawRace(screen);
if (tortX >= 985)
{
screen.setFont(new Font("Times New Roman", Font.ITALIC, 48));
screen.drawString("Tortoise Wins", 650, 240);
clearCurrent(screen);
fillNext(screen);
}
else if (hareX >= 985)
{
screen.setFont(new Font("Times New Roman", Font.ITALIC, 48));
screen.drawString("Tortoise Wins", 650, 240);
clearCurrent(screen);
fillNext(screen);
}
else
{
screen.drawString(("Turn " + turnNum), 621, 55);
screen.setFont(new Font("Times New Roman", Font.ITALIC, 12));
screen.drawString(tMove, 59, 65); screen.drawString(hMove, 66, 255);
clearCurrent(screen);
fillNext(screen);
}
stop();
}
public void clearCurrent( Graphics s )
{
s.clearRect(tortX+1, tortY+1, WIDTH-1, HEIGHT-1);
s.clearRect(hareX+1, hareY+1, WIDTH-1, HEIGHT-1);
}
public void fillNext( Graphics s )
{
s.fillRect(tortX+1, tortY+1, WIDTH-1, HEIGHT-1);
s.fillRect(hareX+1, hareY+1, WIDTH-1, HEIGHT-1);
}
public void drawRace( Graphics s )
{
// Initium
s.drawRect(250, 100, 750, 50);
s.drawRect(250, 300, 750, 50);
int lineX = 265, lineYi = 100, lineYf = 150;
for (int i = 1; i <= 98; i++)
{
if (lineX == 1000)
{
lineX = 265; lineYi = 300; lineYf = 350;
}
s.drawLine(lineX, lineYi, lineX, lineYf);
lineX += 15;
}
s.fillRect(tortX+1, tortY+1, WIDTH-1, HEIGHT-1);
s.fillRect(hareX+1, hareY+1, WIDTH-1, HEIGHT-1);
s.drawImage(tortoise, 59, 80, this);
s.drawImage(hare, 66, 271, this);
s.setFont(new Font("Times New Roman", Font.BOLD, 24));
s.drawString("Race", 250, 55);
}
public void delay()
{
for (int i = 0; i < 90000000; i++)
{
}
}
public void stop()
{
}
}
最佳答案
看起来tMove或hMove(或两者)都是null。在某些情况下，control() 中的 switch 语句似乎可以使这些未分配。要么确保 tMove 和 hMove 在绘制屏幕之前明确分配，或者(也许更好，因为不能保证 control() 会被在绘制小程序之前调用)替换此代码:
screen.drawString(tMove, 59, 65);
screen.drawString(hMove, 66, 255);
这样:
if (tMove != null) {
screen.drawString(tMove, 59, 65);
}
if (hMove != null) {
screen.drawString(hMove, 66, 255);
}
关于java - 龟兔赛跑小程序，如何才能让我的代码正常工作？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/19342727/