问当用户键入数字时，中间的四位数显示为通配符

EN

import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
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 Test {

    public Test() {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                JFrame frame = new JFrame("Test");
                frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

                //create instance of our custom DocumentFiler class
                PhoneNumberFilter phoneNumberFilter = new PhoneNumberFilter(6, 10, '*');


                JTextField jtf = new JTextField(10);
                //add filter to JTextField
                ((AbstractDocument) jtf.getDocument()).setDocumentFilter(phoneNumberFilter);
                frame.add(jtf);

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

                //jtf.setText("0119887654");
            }
        });
    }

    public static void main(String[] args) {
        new Test();
    }
}

class PhoneNumberFilter extends DocumentFilter {

    private int textLength = 0;//keeps track of length of text within the field (used to check if we should start applying the mask)
    private int numberMaskStartIndex;
    private int numberMaskEndIndex;
    private String mask;//what the characters in the specified ranges positions will be replaced with

    public PhoneNumberFilter(int start, int end, char mask) {
        numberMaskStartIndex = start;
        numberMaskEndIndex = end - 1;
        this.mask = String.valueOf(mask);
    }

    @Override
    public void replace(FilterBypass fb, int i, int i1, String string, AttributeSet as) throws BadLocationException {
        if (string.length() > 1) {
            for (int n = string.length() - 1; n >= 0; n--) {//an inserted string may be more than a single character i.e copy and pasting a number
                char c = string.charAt(n);//get a single character of the string
                if (n >= numberMaskStartIndex && n <= numberMaskEndIndex) {//check if its between the range which we should mask
                    super.replace(fb, i, i1, mask, as);
                } else {
                    super.replace(fb, i, i1, String.valueOf(c), as);
                }
                textLength++;
            }
        } else if (textLength >= numberMaskStartIndex && textLength <= numberMaskEndIndex) {//only a singe character was inserted and its between the range which we should mask
            super.replace(fb, i, i1, mask, as);
            textLength++;
        } else {
            super.replace(fb, i, i1, string, as);
            textLength++;
        }
    }

    @Override
    public void remove(FilterBypass fb, int i, int i1) throws BadLocationException {
        super.remove(fb, i, i1);
        if (i == 0 && i1 == textLength) {//if the text removed is the entire textfield i.e CTRL+A or Mouse dragged and DEL than we reset our counter which keeps track of the number of characters in the textfield
            textLength = 0;
        } else {//only a single character was deleted
            textLength--;
        }
    }

    @Override
    public void insertString(FilterBypass fb, int i, String string, AttributeSet as) throws BadLocationException {
        super.insertString(fb, i, string, as);
    }
}