我正在做一个作业计划者，其中一个人在JTextArea中输入当天的作业。我将JTextAreas设为静态，因此可以在类外部访问它们。为了清理代码，我决定使用for循环并将JTextAreas放入静态实例变量数组中。但是，当我尝试通过数组访问JTextArea时，出现了NullPointerException。这是一个声明JTextArea的示例：
static JTextArea MondayEng;
数组（每个主题一个）声明为：
static JTextArea[] Eng = new JTextArea[]{
MondayEng,
TuesdayEng,
WednesdayEng,
ThursdayEng,
FridayEng
};
然后有一个
JTextArea[][]包含数组：static JTextArea[][] subjs = new JTextArea[][] {Eng, Hist, Math, Sci, Lang};
JTextAreas在JFrame（称为PWin）内部实例化，如下所示：
MondayEng = new JTextArea();
MondayEng.setBounds(664, 68, 153, 100);
contentPane.add(MondayEng);
我将尝试获取JTextAreas的内容，如下所示：
for (int i = 0; i < PWin.subjs.length; i++) { // Iterate through subjects
String sub = subjects[i]; // Store the current subject in a variable
for (int y = 0; y < days.length; y++) { // Iterate through days in week
String day = days[y]; // Store the current day in a variable
String str = PWin.subjs[i][y].getText(); // Get the text of the JTextArea currently selected, plop it in a string
保存文件时这是例外：
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at PSave.<init>(PSave.java:19)
at PWin$1.actionPerformed(PWin.java:262)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2028)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2351)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:387)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:242)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:236)
at java.awt.Component.processMouseEvent(Component.java:6373)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3267)
at java.awt.Component.processEvent(Component.java:6138)
at java.awt.Container.processEvent(Container.java:2085)
at java.awt.Component.dispatchEventImpl(Component.java:4735)
at java.awt.Container.dispatchEventImpl(Container.java:2143)
at java.awt.Component.dispatchEvent(Component.java:4565)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4621)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4282)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4212)
at java.awt.Container.dispatchEventImpl(Container.java:2129)
at java.awt.Window.dispatchEventImpl(Window.java:2478)
at java.awt.Component.dispatchEvent(Component.java:4565)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:679)
at java.awt.EventQueue.access$000(EventQueue.java:85)
at java.awt.EventQueue$1.run(EventQueue.java:638)
at java.awt.EventQueue$1.run(EventQueue.java:636)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:98)
at java.awt.EventQueue$2.run(EventQueue.java:652)
at java.awt.EventQueue$2.run(EventQueue.java:650)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.AccessControlContext$1.doIntersectionPrivilege(AccessControlContext.java:87)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:649)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:296)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:211)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:196)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:188)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:122)
任何帮助将不胜感激！
最佳答案
似乎您的问题是，在创建数组时，尚未构造JTextAreas。 Java是按值传递的，因此当您传递稍后要构造的JTextAreas的名称时，它与传递null相同。