我正在为我正在上课的课程设置一个程序。所有代码都已提供，我已将所有内容配置到 Eclipse 中。我还必须becker.jar在库 -> 类路径中用作外部 jar 文件。当我运行程序时，会出现关于NullPointerException.
我已经尝试将 becker.jar 更改为模块路径而不是类路径，但是 Eclipse 找不到该文件。我还尝试重新安装becker.jar以及重做项目的整个设置。
这是我要设置的代码：
import becker.robots.*;
/*
Starting Template:
This file was created in order to provide you with a pre made
'starter' program
*/
public class Starting_Template extends Object {
public static void main(String[] args) {
City toronto = new City();
Robot jo = new Robot(toronto, 3, 0, Direction.EAST, 0);
new Thing(toronto, 3, 2);
jo.move();
jo.turnLeft();
}
}
运行时出现此错误：
Exception in thread "main" java.lang.NullPointerException
at java.desktop/sun.font.FontDesignMetrics.getDefaultFrc(FontDesignMetrics.java:158)
at java.desktop/sun.font.FontDesignMetrics.getMetrics(FontDesignMetrics.java:279)
at java.desktop/sun.swing.SwingUtilities2.getFontMetrics(SwingUtilities2.java:1183)
at java.desktop/javax.swing.JComponent.getFontMetrics(JComponent.java:1646)
at java.desktop/javax.swing.plaf.basic.BasicLabelUI.getPreferredSize(BasicLabelUI.java:245)
at java.desktop/javax.swing.JComponent.getPreferredSize(JComponent.java:1680)
at java.desktop/javax.swing.JSlider.updateLabelUIs(JSlider.java:853)
at java.desktop/javax.swing.JSlider.setLabelTable(JSlider.java:824)
at becker.robots.x.<init>(SourceFile:32)
at becker.robots.RobotUIComponents.<init>(SourceFile:87)
at becker.robots.RobotUIComponents.<init>(SourceFile:110)
at becker.robots.City.a(SourceFile:228)
at becker.robots.City.<init>(SourceFile:97)
at becker.robots.City.<init>(SourceFile:47)
at Starting_Template.main(Starting_Template.java:10)