java - 如何从 JTextField 读取 int 值？

Question

这个问题已经有答案了:

What is a NullPointerException, and how do I fix it? (12 个回答)

已关闭 6 年前。

我的表单上有 2 个 JTextField，并且我全局声明了这 2 个变量

   int order = Integer.parseInt(textOrder.getText());
   int history = Integer.parseInt(textHistory.getText());

但我遇到了这些错误。

    java.lang.NullPointerException
at FrameController.<init>(FrameController.java:39)//this is line 39: int history=Integer.parseInt(textHistory.getText());

at FrameController$1.run(FrameController.java:56)//this is line 56:     FrameController window = new FrameController();
at java.awt.event.InvocationEvent.dispatch(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$500(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.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

JTextField textOrder=new JTextField();
textOrder.getText() // NullPointerException if the document is null

根据文档getText()返回此TextComponent中包含的文本。如果底层文档为 null，将给出 NullPointerException。

如果您使用这些构造函数之一，则文档为空。

JTextField()、JTextField(String text)、JTextField(int columns)、JTextField(String text, int columns) )