Java Swing空指针异常do-while

Question

我正在开发一个简单的系统，该系统从通过一系列按钮事件选择的数组中收集元素，将其复制到一个名为“oneRay”的新数组中，然后循环遍历其元素以测试用户的知识.如果用户从提示中正确识别出答案，则该部分中二维数组的第一个元素变为“”，并使用以下代码跳过：

        do{
        pick = random.nextInt(oneRay.length);
    }while(!(oneRay[pick][0].equals("")));

继续返回上述异常。以下代码将随机创建为相关类的成员：

Random random = new Random()

那么我做错了什么？ 任何帮助将不胜感激。

更新：是的，这些元素是通过一系列 switch 语句初始化的，这些语句将正确的选定数组定向到 oneRay

错误报告很大，因为它是在我尝试构建 swing UI 时启动的，所以它左右抛出故障

这是我用于初始化的内容：

switch(subject){
    case 1:
        switch(unit){
        case 1: oneRay = new String[Master.SciChemArray_IntroductionANDFirstChapter.length][2];
           for(int i = 0; (Master.SciChemArray_IntroductionANDFirstChapter.length) > i; i++){
               oneRay[i][0] = Master.SciChemArray_IntroductionANDFirstChapter[i][0];oneRay[i][1] = Master.SciChemArray_IntroductionANDFirstChapter[i][1];}
        default: System.exit(0); break;
        } break;
    case 2:
        switch(unit){
        case 1: 
            oneRay = new String[Master.MathaRay_Part2.length][2];
           for(int i = 0; (Master.MathaRay_Part2.length) > i; i++){
               oneRay[i][0] = Master.MathaRay_Part2[i][0]; oneRay[i][1] = Master.MathaRay_Part2[i][1];} break;
        default: System.exit(0); break;
        } break;

在创建此设置时，我传递了一个对应于主题和单元号的数字，然后用于复制相关数组，就像这样^^

Unit 和 Subject 是这样传递的：

         mathstatb1.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent l) {
            new SwingImplementation(2, 1);
        }}); 

通过一个按钮发送主题 2 和单元 1

这里是错误，现在在底部，如果有人真的想要它们：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at wbh.SwingImplementation.<init>(SwingImplementation.java:60)
at wbh.matstatMenu$1.actionPerformed(matstatMenu.java:23)
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$200(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)

Answer 1

尝试确保所有 oneRay 数组值都正确初始化。

以下行似乎最适合 NullPointer。如果您尝试为 null 调用 .equals() 方法，则会抛出 NullPointer。

oneRay[pick][0].equals("");

Answer 2

如果你粘贴整个代码会更清楚。在当前代码中，我看到以下内容可能会抛出一个空指针：

!(oneRay[pick][0].equals(""))

改成

!("".equals(oneRay[pick][0]))