java - 单击按钮后需要读取两个 JTextfield 的输入

Question

我正在开发一个程序，该程序启动一个小程序，该小程序将演示扩展欧几里得算法的执行方式。我有两个 JTextFields，将输入值并需要读取/转换为整数等。我在实际读取输入值时遇到困难。

更新的问题:
阅读第一个答案后，我对代码进行了更改。我没有使用 DocumentListener，而是按照建议在 actionPerformed 方法中执行所有操作，但当我尝试测试时，我仍然遇到错误。

这是我当前执行的操作:

public void actionPerformed(ActionEvent event) {
    System.out.println(event.getActionCommand());
    String quotient = "";
    nText = nField.getText();
    mText = mField.getText();

    if("Find GCD".equals(event.getActionCommand())){
        int nInt = Integer.parseInt(nText);
        int mInt = Integer.parseInt(mText);
        int q = mInt/nInt;
        quotient = (Integer.toString(q));
    }
    else quotient = "n/a";
    //NOT the gcd, just to see if this will display
    gcd.setText(quotient);
    gcd.setEditable(false);
}

(注意:gcd是另一个JTextField，但只需要显示结果)

现在，单击按钮后，我会在控制台中打印出这些错误:

Exception in thread "AWT-EventQueue-1" java.lang.NullPointerException at EuclidApplet.actionPerformed(EuclidApplet.java:87) 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$000(Unknown Source) at java.awt.EventQueue$1.run(Unknown Source) at java.awt.EventQueue$1.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source) at java.security.AccessControlContext$1.doIntersectionPrivilege(Unknown Source) at java.awt.EventQueue$2.run(Unknown Source) at java.awt.EventQueue$2.run(Unknown Source) at java.security.AccessController.doPrivileged(Native Method) at java.security.AccessControlContext$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)

我在设置的行收到 NullPointerException

nText = nField.getText();

但我仍然不确定为什么我无法获取已插入到 JTextField 中的文本。我发现的每个例子都表明这应该可行，但我无法实现。谢谢。

Answer 1

I'm getting a NullPointerException at the line where I set nText = nField.getText();

这可能是因为您将 nField 定义为类变量和局部变量。问题是您试图引用为 null 的类变量。

解决方案是去掉类变量。