在Java文本字段中使用鼠标选择粘贴/替换字符（具有指定的字符限制）

我扩展了DocumentFilter类，将要输入的字符数限制为文本字段中指定的数字。这是我的SSCE：

主要类别：

import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.Font;
import java.net.*;
import java.io.*;
import java.util.Date;
import java.util.StringTokenizer;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
import javax.swing.WindowConstants;
import javax.swing.text.PlainDocument;

public class Sandbox implements Runnable {
    private JFrame frame;
    private JTextField inputField;
    private JButton searchButton; 
    private int MAX_CHAR_LIMIT = 1;

    public Sandbox() {
        inputField = new JTextField(); 
        inputField.setColumns(10);
        inputField.setFont(new Font(null, Font.BOLD, 20));
    }

    @Override
    public void run() {
        frame = new JFrame("SSCE");
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        frame.setPreferredSize(new Dimension(500, 300));

        PlainDocument doc = (PlainDocument) inputField.getDocument();
        doc.setDocumentFilter(new DocumentCharLimitFilter(MAX_CHAR_LIMIT));
        frame.getContentPane().setLayout(new FlowLayout());
        frame.getContentPane().add(inputField);

        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String args[]) {
        SwingUtilities.invokeLater(new Sandbox());
    }

}

DocumentCharLimitFilter类

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

public class DocumentCharLimitFilter extends DocumentFilter {

    private int MAX_CHAR_LIMIT;

    public DocumentCharLimitFilter(int maxChars) {
        this.MAX_CHAR_LIMIT = maxChars;
    }

    // You don't need insertString() when entering text in JTextField. 
    @Override
public void replace(FilterBypass fb, int offset, int length, String newText, AttributeSet aSet) throws BadLocationException {
    int oldTextLength = fb.getDocument().getLength();
    String oldText = fb.getDocument().getText(0, oldTextLength);
    String combinedText = oldText + newText;        

    if (combinedText.length() <= MAX_CHAR_LIMIT) {
        super.replace(fb, offset, length, newText, aSet);

        // paste characters upto maximum allowed limit 
    } else if (oldTextLength < MAX_CHAR_LIMIT) {
        int cutPosition = MAX_CHAR_LIMIT - oldTextLength;
        String cutToFit = newText.substring(0, cutPosition);
        super.replace(fb, offset, length, cutToFit, aSet);

    } else {
        System.out.println("Character limit of " + MAX_CHAR_LIMIT + " exceeded.");
    }
}
}

---

您将忽略传递给replace方法的

length

参数，该参数包含要替换的现有字符数

---

如果突出显示JText字段中的一个或多个字符，然后键入或粘贴一些新文本，

length

将包含正值。JTextField内容的新长度将是

oldTextLength-length+newText.length（）

（除非您更改它）。

尝试中的

DocumentFilter

，查看该筛选器是否有效。然后将代码与工作代码进行比较，看看有什么不同。您将忽略传递给replace方法的

length

参数，该参数包含要替换的现有字符数。另外，我很好奇“在JTextField中输入文本时不需要insertString（）”是从哪里来的；我以前从来没有听说过。@VGR我想这些字符没有被替换。新字符将附加到旧字符。这里如何使用length参数？当我使用inserString（）时，它从未被调用。它总是转到replace（）@卡米克：是的。事实上，我用它作为基础来编写我的类。如果你看到了，我有和这里显示的例子相同的first-If语句。我还实现了该示例中暗示的第二个if。例如，如果突出显示一个或多个字符，然后键入或粘贴一些新文本，

length

将包含正值。JTextField内容的新长度将是

oldTextLength-length+newText.length（）

（除非您更改它）。

@Override
public void replace(FilterBypass fb, int offset, int length, String newText, AttributeSet aSet) throws BadLocationException {
    System.out.println(fb.getClass());
    int oldTextLength = fb.getDocument().getLength();
    String oldText = fb.getDocument().getText(0, oldTextLength);
    String combinedText = oldText + newText;

    if (combinedText.length() <= MAX_CHAR_LIMIT) {
        super.replace(fb, offset, length, newText, aSet);

        // paste characters upto maximum allowed limit 
    } else if (oldTextLength < MAX_CHAR_LIMIT) {
        int cutPosition = MAX_CHAR_LIMIT - oldTextLength;
        String cutToFit = newText.substring(0, cutPosition);
        super.replace(fb, offset, length, cutToFit, aSet);

        // NEW CODE 
        // http://stackoverflow.com/questions/42512743/pasting-replacing-a-character-using-mouse-selection-in-java-textfield-with-spec
        // length indicates number of characters highlighted using mouse or keyboard. This will work only when 
        // the entire text is highlighted (if entire text is not highlighted, it would get complicated)
        // and when it is highlighted, I make sure that the new text to be pasted is within limits of the MAX_CHAR_LIMIT
    } else if (length == MAX_CHAR_LIMIT) {
        String correctedString = newText;
        if (newText.length() > MAX_CHAR_LIMIT) {
            correctedString = newText.substring(0, MAX_CHAR_LIMIT);
        }
        super.replace(fb, offset, length, correctedString, aSet);

    } else {
        System.out.println("Entered characters exceed specified limit of " + MAX_CHAR_LIMIT + "exceeded.");
    }
}