Question

我正在制作GUI。用户以整数形式输入年份，并在GUI上显示该年份。但问题是我只想从用户输入4个整数。如果用户输入5个整数值，则显示JOptionPane消息，请再次输入。但我不知道该怎么办。

代码：

public class A extends JFrame{


    private JTextField tx;
    private JLabel year;
    private JButton bt;
    private JLabel at;


    public A(){
        super("Frame");


        getContentPane().setLayout(null);


        tx= new JTextField();
        tx.setBounds(150, 165, 128, 27);
        getContentPane().add(tx);   

        year= new JLabel("Enter Year :");
        year.setBounds(178, 133, 69, 27);
        getContentPane().add(year);


        at= new JLabel();
        at.setFont(new Font("Tahoma", Font.PLAIN, 17));
        at.setBounds(165, 295, 189, 27);
        getContentPane().add(at);


        bt= new JButton("Submit");
        bt.setBounds(178, 203, 84, 27);
        getContentPane().add(bt);
        bt.addActionListener(new ActionListener(){
            public void actionPerformed(ActionEvent arg0) {

                String w = tx.getText();
                int p = Integer.parseInt(w);

                 at.setText(""+p);

            }

        });

        setSize(450,450);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLocationRelativeTo(null);
        setResizable(false);
        setVisible(true);


    }

}

主要

public class Main {

    public static void main(String[] args) {

        A obj = new A();


    }

}

Answer 1

以下是代码，供您快速查看，但请在将来尝试自行实施。

import java.awt.*;
import javax.swing.*;
import javax.swing.text.AbstractDocument;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.DocumentFilter;
import javax.swing.text.DocumentFilter.FilterBypass;

public class MyDocumentFilterExample {

    private static final int MAX_CHARACTERS = 4;
    private JTextField tField;

    private void displayGUI () {
        JFrame frame = new JFrame("Input Integer Example");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

        JPanel contentPane = new JPanel();
        contentPane.setBorder(
            BorderFactory.createEmptyBorder(5, 5, 5, 5));
        tField = new JTextField(10);
        ((AbstractDocument)tField.getDocument()).setDocumentFilter(
                new MyDocumentFilter ( MAX_CHARACTERS ));        
        contentPane.add(tField); 

        frame.setContentPane(contentPane);
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

    public static void main ( String[] args ) {
        Runnable runnable = new Runnable () {
            @Override
            public void run () {
                new MyDocumentFilterExample ().displayGUI ();
            }
        };
        EventQueue.invokeLater ( runnable );
    }
}

class MyDocumentFilter extends DocumentFilter {

    private int max_Characters;
    private boolean DEBUG;

    public MyDocumentFilter(int max_Chars) {
        max_Characters = max_Chars;
        DEBUG = false;
    }

    public void insertString(FilterBypass fb
                                    , int offset
                                    , String str
                                    , AttributeSet a) 
                                    throws BadLocationException {
        if (DEBUG) {
            System.out.println("In DocumentSizeFilter's insertString method");
        }
        int length = fb.getDocument ().getLength () + str.length ();
        if (length <= max_Characters && isValid ( str ) ) 
            super.insertString(fb, offset, str, a);
        else 
            Toolkit.getDefaultToolkit().beep();
    }

    public void replace(FilterBypass fb
                            , int offset, int length
                            , String str, AttributeSet a)
                                throws BadLocationException {
        if (DEBUG) {
            System.out.println("In DocumentSizeFilter's replace method");
        }
        int len = fb.getDocument ().getLength () + str.length ();
        if (len - length <= max_Characters && isValid ( str ) ) 
            super.replace(fb, offset, length, str, a);
        else
            Toolkit.getDefaultToolkit().beep();
    }

    private boolean isValid ( String string ) {
        int len = string.length();
        boolean isValidInteger = true;

        for (int i = 0; i < len; i++)
        {
            if (!Character.isDigit(string.charAt(i)))
            {
                isValidInteger = false;
                break;
            }
        }
        return isValidInteger;
    }
}

Answer 2

只是不要让他们在第一时间输入超过4个字符

tx.addKeyListener(new KeyAdapter() {
      @Override
      public void keyTyped(KeyEvent e) {
          if (tx.getText().length() >= 4) {
              e.consume();
          }
      }
  });

然后你也可以展开它以确保它们也只输入数字

tx.addKeyListener(new KeyAdapter() {
      @Override
      public void keyTyped(KeyEvent e) {
          if (tx.getText().length() >= 4 || !Character.isDigit(e.getKeyChar())) {
              e.consume();
          }
      }
  });

Answer 3

简而言之，您正在检查用户是否输入了有效年份。在这种情况下，逻辑方法会好得多。在实际情况中，每个应用程序都有一定的用户年份范围。你可以这样做。

String w = tx.getText();
int p = Integer.parseInt(w);
int lower_limit = 1960;
int upper_limit = 2050;
if(p>lower_limit && p<uppper_limit){
   at.setText(""+p);
}

但最好的方法是使用JSpinner。它符合目的。

注意：如果您真的想要所有4位数年份，请分别将upper_limit和lower_limit替换为10000和999。

Answer 4

    String w = tx.getText();
            int p = Integer.parseInt(w);

            String e=String.valueOf(w);
    int m = e.length();
    System.out.println(m);

    if(e.length()==4){


             at.setText(""+p);
    }
    else{
        JOptionPane.showMessageDialog(null, "Wrong");
    }
        }   

    });

伙计们这件事有益于实践

Java Swing TextField整数值问题

4 个答案: