Question

我只是在学习Java异常处理和Java。我创建了一个Swing GUI，用户将整数输入两个字段，然后单击带有算术功能的单选按钮，答案将出现在第三个文本字段中。我希望包含一个try / catch块来捕获异常，如果用户将前两个字段中的一个留空或输入除整数之外的其他字段，如果用户试图除以零则返回第二个字段。该表单在功能上有效，但不会捕获错误，只返回堆栈跟踪并使程序崩溃。我有一种感觉，我只是在错误的地方有try / catch块，但是我越是将它移动到更糟糕的地方。有人可以指出我哪里出错了吗？

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.ButtonGroup;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JRadioButton;
import javax.swing.JTextField;

import javax.swing.WindowConstants;
import javax.swing.SwingUtilities;

public class Main extends javax.swing.JFrame {
    private JTextField aTextField;
    private JRadioButton dRadioButton;
    private ButtonGroup buttonGroup;
    private JLabel aLabel;
    private JRadioButton cRadioButton;
    private JRadioButton bRadioButton;
    private JRadioButton aRadioButton;
    private JTextField cTextField;
    private JTextField bTextField;

    /**
     * Auto-generated main method to display this JFrame
     */
    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                Main inst = new Main();
                inst.setLocationRelativeTo(null);
                inst.setVisible(true);
            }
        });
    }

    public Main() {
        super();
        initGUI();
    }

    private void initGUI() {
        try {
            setDefaultCloseOperation(WindowConstants.DISPOSE_ON_CLOSE);
            getContentPane().setLayout(null);
            {
                aTextField = new JTextField();
                getContentPane().add(aTextField);
                aTextField.setBounds(12, 49, 62, 30);
            }
            {
                bTextField = new JTextField();
                getContentPane().add(bTextField);
                bTextField.setBounds(178, 49, 62, 31);
            }
            {
                cTextField = new JTextField();
                getContentPane().add(cTextField);
                cTextField.setBounds(297, 49, 62, 30);
            }
            {
                aRadioButton = new JRadioButton();
                getContentPane().add(aRadioButton);
                aRadioButton.setText("+");
                aRadioButton.setBounds(91, 18, 43, 20);
                aRadioButton.setFont(new java.awt.Font("Segoe UI", 1, 16));
                aRadioButton.addActionListener(new ActionListener() {
                    public void actionPerformed(ActionEvent evt) {
                        aRadioButtonActionPerformed(evt);
                    }
                });
                getButtonGroup().add(aRadioButton);
            }
            {
                bRadioButton = new JRadioButton();
                getContentPane().add(bRadioButton);
                bRadioButton.setText("-");
                bRadioButton.setBounds(91, 53, 43, 20);
                bRadioButton.setFont(new java.awt.Font("Segoe UI", 1, 16));
                bRadioButton.addActionListener(new ActionListener() {
                    public void actionPerformed(ActionEvent evt) {
                        bRadioButtonActionPerformed(evt);
                    }
                });
                getButtonGroup().add(bRadioButton);
            }
            {
                cRadioButton = new JRadioButton();
                getContentPane().add(cRadioButton);
                cRadioButton.setText("*");
                cRadioButton.setBounds(91, 99, 43, 20);
                cRadioButton.setFont(new java.awt.Font("Segoe UI", 1, 16));
                cRadioButton.addActionListener(new ActionListener() {
                    public void actionPerformed(ActionEvent evt) {
                        cRadioButtonActionPerformed(evt);
                    }
                });
                getButtonGroup().add(cRadioButton);
            }
            {
                dRadioButton = new JRadioButton();
                getContentPane().add(dRadioButton);
                getContentPane().add(getALabel());
                dRadioButton.setText("/");
                dRadioButton.setBounds(91, 140, 46, 20);
                dRadioButton.setFont(new java.awt.Font("Segoe UI", 1, 16));
                dRadioButton.addActionListener(new ActionListener() {
                    public void actionPerformed(ActionEvent evt) {
                        dRadioButtonActionPerformed(evt);
                    }
                });
                getButtonGroup().add(dRadioButton);
            }
            pack();
            setSize(400, 300);
        } catch (NumberFormatException e) {
            JOptionPane.showMessageDialog(null,
                    "Error: You must enter an integer");

        } catch (ArithmeticException e) {
            JOptionPane.showMessageDialog(null,
                    "Error: You cannot divide by zero");
        }
    }

    private ButtonGroup getButtonGroup() {
        if (buttonGroup == null) {
            buttonGroup = new ButtonGroup();
        }
        return buttonGroup;
    }

    private JLabel getALabel() {
        if (aLabel == null) {
            aLabel = new JLabel();
            aLabel.setText("=");
            aLabel.setBounds(249, 56, 30, 16);
            aLabel.setFont(new java.awt.Font("Segoe UI", 1, 16));
        }
        return aLabel;
    }

    private void aRadioButtonActionPerformed(ActionEvent evt) {
        String a = aTextField.getText();
        int i = Integer.parseInt(a);
        String b = bTextField.getText();
        int j = Integer.parseInt(b);
        int k = i + j;
        cTextField.setText(Integer.toString(k));
    }

    private void bRadioButtonActionPerformed(ActionEvent evt) {
        String a = aTextField.getText();
        int i = Integer.parseInt(a);
        String b = bTextField.getText();
        int j = Integer.parseInt(b);
        int k = i - j;
        cTextField.setText(Integer.toString(k));
    }

    private void cRadioButtonActionPerformed(ActionEvent evt) {
        String a = aTextField.getText();
        int i = Integer.parseInt(a);
        String b = bTextField.getText();
        int j = Integer.parseInt(b);
        int k = i * j;
        cTextField.setText(Integer.toString(k));
    }

    private void dRadioButtonActionPerformed(ActionEvent evt) {
        String a = aTextField.getText();
        int i = Integer.parseInt(a);
        String b = bTextField.getText();
        int j = Integer.parseInt(b);
        int k = i / j;
        cTextField.setText(Integer.toString(k));
    }

    }


Here is the stack trace I receive:

Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException: For input string: "vvvv"
at java.lang.NumberFormatException.forInputString(Unknown Source)
at java.lang.Integer.parseInt(Unknown Source)
at java.lang.Integer.parseInt(Unknown Source)
at Main.aRadioButtonActionPerformed(Main.java:154)
at Main.access$0(Main.java:152)
at Main$2.actionPerformed(Main.java:78)
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
at javax.swing.JToggleButton$ToggleButtonModel.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$200(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.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.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)

Answer 1

您应该将try catch块放在Integer.parseInt()来电。

Answer 2

你需要将try-catch移动到动作预先形成的方法，现在，它们仅在Java设置GUI时，当用户预先形成动作（actionPreformed）时将调用这些方法，因此它们需要try-catch，而不是设置方法。

private void cRadioButtonActionPerformed(ActionEvent evt) {
    try {

          String a = aTextField.getText();
          int i = Integer.parseInt(a);
          String b = bTextField.getText();
          int j = Integer.parseInt(b);
          int k = i * j;
          cTextField.setText(Integer.toString(k));

       } catch (NumberFormatException e) {
          JOptionPane.showMessageDialog(null,
                "Error: You must enter an integer");

       } catch (ArithmeticException e) {
          JOptionPane.showMessageDialog(null,
                "Error: You cannot divide by zero");
    }
}

将try-catch添加到使用此类似代码的所有ActionPreformed方法中，只需确保每个actionPreformed方法仍然拥有它自己的代码，只需使用它周围的try-catch块

Answer 3

如果你不检查你的每个事件方法，你会得到例外，所以你可以做这样的事情来解决它，

private void aRadioButtonActionPerformed(ActionEvent evt) {
    String a = aTextField.getText();
    String b = bTextField.getText();



    // you may get empty string here so check if the texbox is empty ?
 int i=0,j=0;

        try{

    if(a.length()>0 || b.length()>0){
         i = Integer.parseInt(a);
         j = Integer.parseInt(b);
    }else{
        if(a.length()<1 && b.length()>0){

            i = Integer.parseInt(a);
        }else{
            if(b.length()<1 && a.length()>0)
            j = Integer.parseInt(b);
        }
    }


    int k = i + j;
        }catch(Exception e){
          System.out.println("Exception:"+e);
          }
    cTextField.setText(Integer.toString(k));
}

为你做同样的事情 - ，*，/单选按钮监听器

Java Swing GUI Try / Catch Block

3 个答案: