如何限制 JTextField 中的字符数? [英] How To limit the number of characters in JTextField?

问题描述

如何限制在 JTextField 中输入的字符数?

How to limit the number of characters entered in a JTextField?

假设我想输入最多 5 个字符.之后就不能再输入字符了.

Suppose I want to enter say 5 characters max. After that no characters can be entered into it.

推荐答案

http://www.rgagnon.com/javadetails/java-0198.html

import javax.swing.text.PlainDocument;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;

public class JTextFieldLimit extends PlainDocument {
  private int limit;

  JTextFieldLimit(int limit) {
   super();
   this.limit = limit;
   }

  public void insertString( int offset, String  str, AttributeSet attr ) throws BadLocationException {
    if (str == null) return;

    if ((getLength() + str.length()) <= limit) {
      super.insertString(offset, str, attr);
    }
  }
}

然后

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

 public class DemoJTextFieldWithLimit extends JApplet{
   JTextField textfield1;
   JLabel label1;

   public void init() {
     getContentPane().setLayout(new FlowLayout());
     //
     label1 = new JLabel("max 10 chars");
     textfield1 = new JTextField(15);
     getContentPane().add(label1);
     getContentPane().add(textfield1);
     textfield1.setDocument
        (new JTextFieldLimit(10));
     }
}

(来自谷歌的第一个结果)

(first result from google)

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