Create a 4-digit numeric PIN code input field using JPasswordField

• download example.jar
• download src.zip
• repository

Code

class PinCodeDocumentFilter extends DocumentFilter {
  public static final int MAX = 4;

  @Override public void replace(
      DocumentFilter.FilterBypass fb, int offset,
      int length, String text, AttributeSet attrs) throws BadLocationException {
    String str = fb.getDocument().getText(
      0, fb.getDocument().getLength()) + text;
    if (str.length() <= MAX && str.matches("\\d+")) {
      super.replace(fb, offset, length, text, attrs);
    }
  }
}

class PasswordView2 extends PasswordView {
  public PasswordView2(Element elem) {
    super(elem);
  }

  @Override protected int drawUnselectedText(
      Graphics g, int x, int y, int p0, int p1) throws BadLocationException {
    return drawText(g, x, y, p0, p1);
  }

  // @see drawUnselectedTextImpl(...)
  private int drawText(Graphics g, int x, int y, int p0, int p1)
        throws BadLocationException {
    Container c = getContainer();
    int j = x;
    if (c instanceof JPasswordField) {
      JPasswordField f = (JPasswordField) c;
      if (f.isEnabled()) {
        g.setColor(f.getForeground());
      } else {
        g.setColor(f.getDisabledTextColor());
      }
      Graphics2D g2 = (Graphics2D) g;
      char echoChar = f.getEchoChar();
      int n = p1 - p0;
      // Override BasicPasswordFieldUI#create(Element) to return PasswordView2
      // that makes only trailing digits visible without masking
      for (int i = 0; i < n; i++) {
        j = i == n - 1
            ? drawLastChar(g2, j, y, i)
            : drawEchoCharacter(g, j, y, echoChar);
      }
    }
    return j;
  }

  private int drawLastChar(Graphics g, int x, int y, int p1)
        throws BadLocationException {
    Graphics2D g2 = (Graphics2D) g;
    Font font = g2.getFont();
    float fs = font.getSize2D();
    double w = font.getStringBounds("0", g2.getFontRenderContext()).getWidth();
    int sz = (int) ((fs - w) / 2d);
    Document doc = getDocument();
    Segment s = new Segment(); // SegmentCache.getSharedSegment();
    doc.getText(p1, 1, s);
    // int ret = Utilities.drawTabbedText(s, x, y, g, this, p1);
    // SegmentCache.releaseSharedSegment(s);
    return Utilities.drawTabbedText(s, x + sz, y, g, this, p1);
  }
}

References

• Create a 4-digit numeric PIN code input field using JPasswordField(Japanese)