试试这个课程：
package playground;import java.awt.*;import javax.swing.*;import javax.swing.text.document;@SuppressWarnings("serial")public class PlaceholderTextField extends JTextField { public static void main(final String[] args) { final PlaceholderTextField tf = new PlaceholderTextField(""); tf.setColumns(20); tf.setPlaceholder("All your base are belong to us!"); final Font f = tf.getFont(); tf.setFont(new Font(f.getName(), f.getStyle(), 30)); JOptionPane.showMessageDialog(null, tf); } private String placeholder; public PlaceholderTextField() { } public PlaceholderTextField( final document pDoc, final String pText, final int pColumns) { super(pDoc, pText, pColumns); } public PlaceholderTextField(final int pColumns) { super(pColumns); } public PlaceholderTextField(final String pText) { super(pText); } public PlaceholderTextField(final String pText, final int pColumns) { super(pText, pColumns); } public String getPlaceholder() { return placeholder; } @Override protected void paintComponent(final Graphics pG) { super.paintComponent(pG); if (placeholder == null || placeholder.length() == 0 || getText().length() > 0) { return; } final Graphics2D g = (Graphics2D) pG; g.setRenderingHint( RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON); g.setColor(getDisabledTextColor()); g.drawString(placeholder, getInsets().left, pG.getFontMetrics() .getMaxAscent() + getInsets().top); } public void setPlaceholder(final String s) { placeholder = s; }}
