java - Try and Catch 用于简单的计算器输入

Question

这个用java编写的程序用作计算器。如果用户尝试从结果文本中输入，谁能告诉我如何实现 try/catch block ，以便我可以处理不正确的工作流程？

这是代码:

    package simplecal;

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

 public class SimpleCal extends JFrame {

JTextField jftinput1, jftinput2, jftresult;
JButton jbtminus, jbtadd,jbtdivid, jbttimes;
final int JTEXT_SIZE = 5;
SimpleCal(){
    setLayout(new FlowLayout());
    jftinput1 = new JTextField(JTEXT_SIZE);
    jftinput2 = new JTextField(JTEXT_SIZE);
    jftresult = new JTextField(JTEXT_SIZE);
    add(new JLabel("Input 1: "));
    add(jftinput1);
    add(new JLabel("Input 2: "));
    add(jftinput2);
    add(new JLabel("Result "));
    add(jftresult);
    JPanel p1 = new JPanel();

    jbtminus = new JButton("Subtract");
    jbtadd = new JButton("Add");
    jbttimes = new JButton("Multiple");
    jbtdivid = new JButton("Divided");

    p1.add(jbtminus);
    jbtminus.addActionListener(new ButtonListener1());
    p1.add(jbtadd);
    jbtadd.addActionListener(new ButtonListener2());
    p1.add(jbttimes);
    jbttimes.addActionListener(new ButtonListener3());
    p1.add(jbtdivid);
    jbtdivid.addActionListener(new ButtonListener4());
    add(p1, BorderLayout.SOUTH);

}

class ButtonListener1 implements ActionListener{
    public void actionPerformed(ActionEvent e){
        double input1 = Double.parseDouble(jftinput1.getText());
        double input2 = Double.parseDouble(jftinput2.getText());

        double answer = input1 - input2;

        jftresult.setText(Double.toString(answer));
    }
}

class ButtonListener2 implements ActionListener{
    public void actionPerformed(ActionEvent e){
       double input1 = Double.parseDouble(jftinput1.getText());
        double input2 = Double.parseDouble(jftinput2.getText());

        double answer = input1 + input2;

        jftresult.setText(Double.toString(answer));
    }
}

class ButtonListener3 implements ActionListener{
    public void actionPerformed(ActionEvent e){
       double input1 = Double.parseDouble(jftinput1.getText());
        double input2 = Double.parseDouble(jftinput2.getText());

        double answer = input1 * input2;

        jftresult.setText(Double.toString(answer));
    }
}

class ButtonListener4 implements ActionListener{
    public void actionPerformed(ActionEvent e){
       double input1 = Double.parseDouble(jftinput1.getText());
        double input2 = Double.parseDouble(jftinput2.getText());

        double answer = input1 / input2;

        jftresult.setText(Double.toString(answer));
    }
}

public static void main(String[] args) {
    SimpleCal frame = new SimpleCal();
    frame.setTitle("Simple Cal");
    frame.pack();
    frame.setLocationRelativeTo(null);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setVisible(true);      
    frame.setResizable(false);
    frame.setSize(450,100);
}

}

Answer 1

您不需要为此使用异常处理程序。只需将该字段设置为不可编辑即可:

jftresult.setEditable(false);

参见http://docs.oracle.com/javase/7/docs/api/javax/swing/text/JTextComponent.html#setEditable(boolean) .