Java 由于文本字段，ActionListener中存在空指针？

作为对JavaSwingGUI界面和我即将在学校上的几何课的介绍，我决定为这门课制作一个“特殊”计算器。 现在我有一个空指针在里面，我不太明白是什么导致了它。我编程的方式在我的其他课程中也起作用，那么为什么它在这里不起作用呢

不管怎么说，这里有两个类的错误是在和其他两个工作，我不明白我做了什么不同。 以下是错误：

Exception in thread "AWT-EventQueue-0" java.lang.ExceptionInInitializerError
    at geohelper.GeoFrame.addToGUI(GeoFrame.java:90)
    at geohelper.GeoFrame.showGUI(GeoFrame.java:42)
    at geohelper.GeoHelper$1.run(GeoHelper.java:13)
    at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
    at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:727)
    at java.awt.EventQueue.access$200(EventQueue.java:103)
    at java.awt.EventQueue$3.run(EventQueue.java:688)
    at java.awt.EventQueue$3.run(EventQueue.java:686)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
    at java.awt.EventQueue.dispatchEvent(EventQueue.java:697)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
    at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
    at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
    at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)
Caused by: java.lang.NullPointerException
    at geohelper.RPrismListener.<init>(RPrismListener.java:21)
    at geohelper.RecPrism.<clinit>(RecPrism.java:14)
    ... 17 more

这是它的听众的课程

package geohelper;

import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.DocumentEvent;
import javax.swing.event.DocumentListener;

public class RPrismListener implements ActionListener, DocumentListener {

    private JButton listenbutton;
    private JTextField listenfield[];
    private String s[];
    private boolean failinput = false;
    private boolean hasinput[] = {false, false, false};
    private double y, z;
    private double x[];
    private RecPrism rp = new RecPrism();

    public RPrismListener(JButton jb1, JTextField Jtxt1, JTextField Jtxt2, JTextField Jtxt3) {
        listenbutton = jb1;
        listenfield[0] = Jtxt1;
        listenfield[1] = Jtxt2;
        listenfield[2] = Jtxt3;
    }

    @Override
    public void actionPerformed(ActionEvent ae) {
        for(int d = 0; d < 2; d++) {
            if(hasinput[d]) {
                s[d] = listenfield[d].getText();
                x[d] = Double.parseDouble(s[d]); 
            } else {
                GeoFrame.GLabel.setText("one or more of the text fields haven't been changed.");
                return;
            }
        }
        y = rp.volume(x[0], x[1], x[2]);
        z = rp.surfacearea(x[0], x[1], x[2]);
        GeoFrame.GLabel.setText("The Volume is: " + y + ". The Surface area is: " + z +".");
    }

    @Override
    public void insertUpdate(DocumentEvent de) {
        if(de.getDocument().equals("Length")) {
            hasinput[0] = true;
        } if (de.getDocument().equals("Width")) {
            hasinput[1] = true;
        } if (de.getDocument().equals("Height")) {
            hasinput[2] = true;
        }
    }

    @Override
    public void removeUpdate(DocumentEvent de) {

    }

    @Override
    public void changedUpdate(DocumentEvent de) {

    }

    }

听众

package geohelper;

import javax.swing.*;
import java.awt.event.*;

public class SquareListener implements ActionListener {

    private JButton ListenButton;
    private JTextField ListenField;
    private double x;
    private double y;
    private double z;
    private String s = "1";
    private Square square = new Square();

    public SquareListener(JButton par1, JTextField par2) {
        this.ListenButton = par1;
        this.ListenField = par2;
    }

    @Override
    public void actionPerformed(ActionEvent ae) {
        try {
            s = Square.squarefield.getText();
        } catch(NullPointerException npe) {
            npe.printStackTrace();
        }
        x = Double.parseDouble(s);
        y = square.area(x);
        z = square.perimeter(x);
        GeoFrame.GLabel.setText("The area is: " + y + ". The perimeter is: " + z + ".");
    }

}

---

我想知道的是为什么会生成它以及如何修复它，谢谢。

都在堆栈跟踪中：

Caused by: java.lang.NullPointerException
at geohelper.RPrismListener.<init>(RPrismListener.java:21)

listenField

从未初始化，因此为空

在构造函数的开头添加以下内容：

public RPrismListener(JButton jb1, JTextField Jtxt1, JTextField Jtxt2, JTextField Jtxt3) {
    listenbutton = jb1;
    listenfield[0] = Jtxt1;
    listenfield[1] = Jtxt2;
    listenfield[2] = Jtxt3;
}

listenfield = new JTextField[3];

---

所有这些都在堆栈跟踪中：

Caused by: java.lang.NullPointerException
at geohelper.RPrismListener.<init>(RPrismListener.java:21)

listenField

从未初始化，因此为空

在构造函数的开头添加以下内容：

public RPrismListener(JButton jb1, JTextField Jtxt1, JTextField Jtxt2, JTextField Jtxt3) {
    listenbutton = jb1;
    listenfield[0] = Jtxt1;
    listenfield[1] = Jtxt2;
    listenfield[2] = Jtxt3;
}

listenfield = new JTextField[3];

---

显示堆栈跟踪。它将精确地显示引用空引用的位置（行号）。对不起，忘记了这一点，只是更新了它显示堆栈跟踪的方式。它将精确地显示引用空引用的位置（带有行号）。哦，很抱歉忘记了这一点，只是更新了它。它也没有在正方形中初始化，并且工作正常。在正方形中，您通过分配它

par1

和

par2

来初始化它，因为它不是数组，而是字段。但是

listenfield

是一个数组。在将内容放入数组之前，必须以某种方式构建数组。它也不是在正方形中初始化的，并且该数组工作得很好。在正方形中，通过分配它

par1

和

par2

来初始化它，因为它不是数组，而是字段。但是

listenfield

是一个数组。您必须以某种方式构建阵列，然后才能将内容放入其中。