JTextArea 未设置，抛出错误答案

【问题标题】：JTextArea not setting, throwing up errorJTextArea 未设置，抛出错误
【发布时间】：2015-04-06 15:35:52
【问题描述】：

所以我从数据库中提取信息并将它们放入我的 GUI 中的字段/框中。

houseText 和 addressText 都是文本字段，它们设置得很好，但是 oInfo 是一个 JTextArea，当我尝试设置它时它会导致错误。我也尝试使用“附加”，但它没有改变任何东西。有什么解决办法吗？

infoHolder = dBStatement.executeQuery("SELECT * FROM House");
infoHolder.next();

hName = infoHolder.getString("Name");
hAddress = infoHolder.getString("Address");
numRooms = infoHolder.getInt("numRooms");
Type = infoHolder.getString("Type");
charge = infoHolder.getString("roomCharge");
Access = infoHolder.getString("dAccess");
Info = infoHolder.getString("oInfo");

// the below print prints all the details to prove that the database has been read correctly.
System.out.println(hName + " " + hAddress + " " + numRooms + " " + Type + " " + charge + " " + Access + " " + Info);

houseText.setText(" " + hName); 
addressText.setText(" " + hAddress);
//roomNumber.setSelectedItem(numRooms);
//roomType.setSelectedItem(" " + Type);
//chargeRoom.setSelectedItem(" " + charge);
//access.setSelectedItem(" " + Access);
oInfo.setText(Info);

堆栈跟踪：

java.lang.NullPointerException at FinalBAndB.initialiseDatabase(FinalBAndB.java:124) 
    at FinalBAndB$1.run(FinalBAndB.java:274) 
    at java.awt.event.InvocationEvent.dispatch(Unknown Source) 
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source) 
    at java.awt.EventQueue.access$400(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.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)

【问题讨论】：

您遇到了什么错误，您从哪里调用此代码？它是事件处理程序还是其他线程？
@npinti 我正在从我的公共静态 void main 调用代码。上面的代码在它自己的名为initialiseDatabase()的方法中；文本字段设置完美，但文本区域（oinfo）是问题所在。我在打印堆栈跟踪的方法上有一个异常处理程序，但它不再具有启发性。 infoHolder 是一个结果集。
没有启发乔的可能启发杰克。堆栈跟踪不是 FYEO。
java.lang.NullPointerException at FinalBAndB.initialiseDatabase(FinalBAndB.java:124) at FinalBAndB$1.run(FinalBAndB.java:274) at java.awt.event.InvocationEvent.dispatch（未知来源）在 java.awt.EventQueue.dispatchEventImpl(Unknown Source) at java.awt.EventQueue.access$400(Unknown Source) at java.awt.EventQueue$3.run(Unknown Source) at java.awt.EventQueue$3.run(Unknown Source) ) 在 java.security.AccessController.doPrivileged(Native Method)
在 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) 那是堆栈跟踪。

标签： java get set jtextfield jtextarea

【解决方案1】：

为了完整起见添加答案和其他一些次要信息。

堆栈跟踪：

java.lang.NullPointerException at FinalBAndB.initialiseDatabase(FinalBAndB.java:124) 
    at FinalBAndB$1.run(FinalBAndB.java:274) 
    at java.awt.event.InvocationEvent.dispatch(Unknown Source) 
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source) 
    at java.awt.EventQueue.access$400(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.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)

表示您正在尝试访问未初始化的对象。事实证明是这样的。

附加信息：与许多其他语言一样，Java 使用特定线程来执行其所有 UI 操作。在 Java 中，这称为Event Dispatcher Thread (EDT)。由于您正在更新 UI 组件的文本，因此您需要确保操作通过 EDT 的操作上下文进行。为此，通常会恢复使用SwingUtilities.invokeLater(Runnable runnable)。请确保您遵循此模式以避免任何潜在的跨线程操作问题。

【讨论】：