捕获块字符串/数字验证

Question

在catch块中，如果有人输入一个字符串或一个小于13或大于16的数字，我想打印输入有效的卡片no。

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.BoxLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;

//CreditCard class
public class CreditCard {
    //Variable declaration

    private JFrame frame;
    private JPanel panel;
    private JTextField textField;
    private JLabel label;
    private JLabel resLabel;
    private JButton validateBtn;

    //Constructor
    public CreditCard() {

        frame = new JFrame("Credit Card Details");
        frame.setSize(350, 350);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        // create a new panel and add the frame to the panel.
        panel = new JPanel();
        frame.add(panel);
        panel.setLayout(null);

        // add label
        label = new JLabel("Enter Credit Card No.");
        label.setBounds(10, 20, 165, 25);
        panel.add(label);

        // add input text
        textField = new JTextField(16);
        textField.setBounds(10, 50, 165, 25);
        panel.add(textField);

        // create a validation button
        validateBtn = new JButton("Validate");
        validateBtn.setBounds(10, 80, 80, 25);
        panel.add(validateBtn);

        frame.setVisible(true);

        // set label as valid or invalid
        resLabel = new JLabel();
        resLabel.setBounds(180, 50, 265, 25);
        panel.add(resLabel);

        // add event listener
        validateBtn.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                try {
                String text = textField.getText();
                if (text.length() < 13 || text.length() > 16) {
                    resLabel.setText("Entered Value Must Be Between 13-16 Chars");
                    return;
                }
                boolean isValid = validateText(text);
                if(isValid)
                    resLabel.setText("Credit Card is Valid");
                else
                    resLabel.setText("Credit Card is Invalid");
                }catch(NumberFormatException f){
                    System.out.println("Enter Valid Card Number");
                }

            }

            private boolean validateText(String text) {
                int rSum = 0, lSum = 0;
                for (int i = text.length() - 2; i >= 0; i -= 2) {
                    if (!Character.isDigit(text.charAt(i)))
                        return false;
                    int currentNum = Character.getNumericValue(text.charAt(i));
                    currentNum *= 2;
                    if (currentNum > 9) {
                        int tempSum = 0;
                        while (currentNum >= 10) {
                            tempSum += currentNum % 10;
                            currentNum /= 10;
                        }
                        tempSum += currentNum;
                        currentNum = tempSum;
                    }
                    rSum += currentNum;
                }
                System.out.println(rSum);
                for (int i = text.length() - 1; i >= 0; i -= 2) {
                    if (!Character.isDigit(text.charAt(i)))
                        return false;
                    int currentNum = Character.getNumericValue(text.charAt(i));
                    lSum += currentNum;
                }
                System.out.println(lSum);
                int totalSum = lSum + rSum;
                if (totalSum % 10 == 0)
                    return true;
                return false;
            }

        });
    }
}

Answer 1

如果希望引发异常，则必须将其包含在代码中。您可以通过在希望发生的位置添加“throw new NumberFormatException()”来实现它。

无论如何，在您描述的情况下抛出异常不是最好的主意，因为抛出异常会阻止程序以“正常”的方式运行。我建议使用“if”语句来检查输入--如果输入令您满意，则继续，但如果不满意--则提供下一个输入（在提到的“if”语句周围使用无限while循环，当正确输入完成时结束其工作）或简单地编写错误消息。