java.lang.ArithmeticException 看不出为什么

Question

我正在使用计算器并使用 NetBeans GUI 生成器，因此它可能有点不清楚和令人困惑。(完整代码 http://pastebin.com/ZLcM74ZQ ，因为它太长了)

package rechnerfinal;

/**
 *
 * @author Fredrik
 */
public class RechnerJFrame extends javax.swing.JFrame {

    /**
     * Creates new form RechnerJFrame
     */
    private int value1;
    private int value2;
    private int Rechenoperation;
    public RechnerJFrame() {
        initComponents();
    }

//Generated Code....                       

    private void jButton9ActionPerformed(java.awt.event.ActionEvent evt) {                                         
        // TODO add your handling code here:
        //7
        String labeltextNeu = null;
        String labeltext = jLabel1.getText();
        if(labeltext == "0") {
            setlabeltext(7);
        } else {
            labeltextNeu = labeltext + "7";
            setlabeltext(Integer.valueOf(labeltextNeu));
        }
    }                                        

    private void jButton7ActionPerformed(java.awt.event.ActionEvent evt) {                                         
        //÷
        value1 = Integer.valueOf(jLabel1.getText());
        Rechenoperation = 4;
        jLabel1.setText("0");
    }                                        

    private void jButton21ActionPerformed(java.awt.event.ActionEvent evt) {                                          
        // TODO add your handling code here:
        //1
        String labeltextNeu = null;
        String labeltext = jLabel1.getText();
        if(labeltext == "0") {
            setlabeltext(1);
        } else {
            labeltextNeu = labeltext + "0";
            setlabeltext(Integer.valueOf(labeltextNeu));
        }
    }                                         

    private void jButton17ActionPerformed(java.awt.event.ActionEvent evt) {                                          
        // TODO add your handling code here:
        //1
        String labeltextNeu = null;
        String labeltext = jLabel1.getText();
        if(labeltext == "0") {
            setlabeltext(1);
        } else {
            labeltextNeu = labeltext + "1";
            setlabeltext(Integer.valueOf(labeltextNeu));
        }
    }                                         

    private void jButton10ActionPerformed(java.awt.event.ActionEvent evt) {                                          
        // TODO add your handling code here:
        //8
        String labeltextNeu = null;
        String labeltext = jLabel1.getText();
        if(labeltext == "0") {
            setlabeltext(8);
        } else {
            labeltextNeu = labeltext + "8";
            setlabeltext(Integer.valueOf(labeltextNeu));
        }
    }                                         

    private void jButton11ActionPerformed(java.awt.event.ActionEvent evt) {                                          
        // TODO add your handling code here:
        //9
        String labeltextNeu = null;
        String labeltext = jLabel1.getText();
        if(labeltext == "0") {
            setlabeltext(9);
        } else {
            labeltextNeu = labeltext + "9";
            setlabeltext(Integer.valueOf(labeltextNeu));
        }
    }                                         

    private void jButton13ActionPerformed(java.awt.event.ActionEvent evt) {                                          
        // TODO add your handling code here:
        //4
        String labeltextNeu = null;
        String labeltext = jLabel1.getText();
        if(labeltext == "0") {
            setlabeltext(4);
        } else {
            labeltextNeu = labeltext + "4";
            setlabeltext(Integer.valueOf(labeltextNeu));
        }
    }                                         

    private void jButton14ActionPerformed(java.awt.event.ActionEvent evt) {                                          
        // TODO add your handling code here:
        //5
        String labeltextNeu = null;
        String labeltext = jLabel1.getText();
        if(labeltext == "0") {
            setlabeltext(5);
        } else {
            labeltextNeu = labeltext + "5";
            setlabeltext(Integer.valueOf(labeltextNeu));
        }
    }                                         

    private void jButton15ActionPerformed(java.awt.event.ActionEvent evt) {                                          
       // TODO add your handling code here:
        //6
        String labeltextNeu = null;
        String labeltext = jLabel1.getText();
        if(labeltext == "0") {
            setlabeltext(6);
        } else {
            labeltextNeu = labeltext + "6";
            setlabeltext(Integer.valueOf(labeltextNeu));
        }
    }                                         

    private void jButton18ActionPerformed(java.awt.event.ActionEvent evt) {                                          
        // TODO add your handling code here:
        //2
        String labeltextNeu = null;
        String labeltext = jLabel1.getText();
        if(labeltext == "0") {
            setlabeltext(2);
        } else {
            labeltextNeu = labeltext + "2";
            setlabeltext(Integer.valueOf(labeltextNeu));
        }
    }                                         

    private void jButton19ActionPerformed(java.awt.event.ActionEvent evt) {                                          
        // TODO add your handling code here:
        //3
        String labeltextNeu = null;
        String labeltext = jLabel1.getText();
        if(labeltext == "0") {
            setlabeltext(3);
        } else {
            labeltextNeu = labeltext + "3";
            setlabeltext(Integer.valueOf(labeltextNeu));
        }
    }                                         

    private void jButton16ActionPerformed(java.awt.event.ActionEvent evt) {                                          
        //+
        value1 = Integer.valueOf(jLabel1.getText());
        Rechenoperation = 1;
        jLabel1.setText("0");
    }                                         

    private void jButton24ActionPerformed(java.awt.event.ActionEvent evt) {                                          
        //=
        int Ergebnis;
        switch(Rechenoperation) {
            case 1: //+
                value2 = Integer.valueOf(jLabel1.getText());
                Ergebnis = value1 + value2;
                setlabeltext(Ergebnis);
            case 2: //-
                value2 = Integer.valueOf(jLabel1.getText());
                Ergebnis = value1 - value2;
                setlabeltext(Ergebnis);
            case 3: //x
                value2 = Integer.valueOf(jLabel1.getText());
                Ergebnis = value1 * value2;
                setlabeltext(Ergebnis);
            case 4: //:
                value2 = Integer.valueOf(jLabel1.getText());
                Ergebnis = value1 / value2;
                setlabeltext(Ergebnis);
        }
        Ergebnis = 0;
    }                                         

    private void jButton23ActionPerformed(java.awt.event.ActionEvent evt) {                                          
        //AC
        jLabel1.setText("0");
        value1 = 0;
        value2 = 0;
        Rechenoperation = 0;
    }                                         

    private void jButton12ActionPerformed(java.awt.event.ActionEvent evt) {                                          
        //-
        value1 = Integer.valueOf(jLabel1.getText());
        Rechenoperation = 2;
        jLabel1.setText("0");
    }                                         

    private void jButton8ActionPerformed(java.awt.event.ActionEvent evt) {                                         
        //*
        value1 = Integer.valueOf(jLabel1.getText());
        Rechenoperation = 3;
        jLabel1.setText("0");
    }                                        

    private void jButton22ActionPerformed(java.awt.event.ActionEvent evt) {                                          
        // TODO add your handling code here:
    }                                         

    private void jButton5ActionPerformed(java.awt.event.ActionEvent evt) {                                         
        // TODO add your handling code here:
    }                                        


    public void setlabeltext(int labelwert) {
        jLabel1.setText(Integer.toString(labelwert));
    }
    /**
     * @param args the command line arguments
     */
    public static void main(String args[]) {
        /* Set the Nimbus look and feel */
        //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
        /* If Nimbus (introduced in Java SE 6) is not available, stay with the default look and feel.
         * For details see http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html 
         */
        try {
            for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
                if ("Nimbus".equals(info.getName())) {
                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (ClassNotFoundException ex) {
            java.util.logging.Logger.getLogger(RechnerJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(RechnerJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(RechnerJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(RechnerJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }
        //</editor-fold>

        /* Create and display the form */
        java.awt.EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                new RechnerJFrame().setVisible(true);
            }
        });
    }

    // Variables declaration - do not modify                     
    private javax.swing.JButton jButton1;
    private javax.swing.JButton jButton10;
    private javax.swing.JButton jButton11;
    private javax.swing.JButton jButton12;
    private javax.swing.JButton jButton13;
    private javax.swing.JButton jButton14;
    private javax.swing.JButton jButton15;
    private javax.swing.JButton jButton16;
    private javax.swing.JButton jButton17;
    private javax.swing.JButton jButton18;
    private javax.swing.JButton jButton19;
    private javax.swing.JButton jButton2;
    private javax.swing.JButton jButton20;
    private javax.swing.JButton jButton21;
    private javax.swing.JButton jButton22;
    private javax.swing.JButton jButton23;
    private javax.swing.JButton jButton24;
    private javax.swing.JButton jButton3;
    private javax.swing.JButton jButton4;
    private javax.swing.JButton jButton5;
    private javax.swing.JButton jButton6;
    private javax.swing.JButton jButton7;
    private javax.swing.JButton jButton8;
    private javax.swing.JButton jButton9;
    private javax.swing.JLabel jLabel1;
    // End of variables declaration                   
}

这是我收到的错误:

Exception in thread "AWT-EventQueue-0" java.lang.ArithmeticException: / by zero
at rechnerfinal.RechnerJFrame.jButton24ActionPerformed(RechnerJFrame.java:451)
at rechnerfinal.RechnerJFrame.access$1700(RechnerJFrame.java:8)
at rechnerfinal.RechnerJFrame$18.actionPerformed(RechnerJFrame.java:212)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2022)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2348)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
at java.awt.Component.processMouseEvent(Component.java:6533)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3324)
at java.awt.Component.processEvent(Component.java:6298)
at java.awt.Container.processEvent(Container.java:2236)
at java.awt.Component.dispatchEventImpl(Component.java:4889)
at java.awt.Container.dispatchEventImpl(Container.java:2294)
at java.awt.Component.dispatchEvent(Component.java:4711)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4888)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4525)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4466)
at java.awt.Container.dispatchEventImpl(Container.java:2280)
at java.awt.Window.dispatchEventImpl(Window.java:2746)
at java.awt.Component.dispatchEvent(Component.java:4711)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:758)
at java.awt.EventQueue.access$500(EventQueue.java:97)
at java.awt.EventQueue$3.run(EventQueue.java:709)
at java.awt.EventQueue$3.run(EventQueue.java:703)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:86)
at java.awt.EventQueue$4.run(EventQueue.java:731)
at java.awt.EventQueue$4.run(EventQueue.java:729)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:728)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

此外，jLabel 没有显示计算结果，尽管在使用 System.out.println 进行测试时，它给了我正确的解决方案。我完全不知道是什么原因导致这种情况。

Answer 1

您的 switch 语句中有几个问题:

switch(Rechenoperation) {
            case 1: //+
                value2 = Integer.valueOf(jLabel1.getText());
                Ergebnis = value1 + value2;
                setlabeltext(Ergebnis);
                break;
            case 2: //-
                value2 = Integer.valueOf(jLabel1.getText());
                Ergebnis = value1 - value2;
                setlabeltext(Ergebnis);
                break;
            case 3: //x
                value2 = Integer.valueOf(jLabel1.getText());
                Ergebnis = value1 * value2;
                setlabeltext(Ergebnis);
                break;
            case 4: //:
                value2 = Integer.valueOf(jLabel1.getText());
                if(value2 != 0){ //Add a safeguard if value2 is '0'
                    Ergebnis = value1 / value2;
                    setlabeltext(Ergebnis);
                } else {
                    setlabeltext("NaN");
                }
                break;
        }

您需要打破每种情况的逻辑。这使得事情变得更有效率，是一种很好的做法。另外，在除法之前检查value2是否为零。

正如 FredK 指出的，您可以在 switch 语句之后setlabeltext 并在 switch 语句之前获取 value2。无论如何，效率最多并不重要，因为您的 break 语句，这些将被执行一次，但这种方式仍然更适合维护。