當JTextField沒有輸入時，顯示提示文字，類似於

通過實現FocusListener來實現。

import java.awt.Color;
import java.awt.event.FocusEvent;
import java.awt.event.FocusListener;

import javax.swing.JTextField;

public class JTextFieldHintListener implements FocusListener {
	private String hintText;
	private JTextField textField;
	public JTextFieldHintListener(JTextField jTextField,String hintText) {
		this.textField = jTextField;
		this.hintText = hintText;
		jTextField.setText(hintText);  //預設直接顯示
		jTextField.setForeground(Color.GRAY);
	}

	@Override
	public void focusGained(FocusEvent e) {
		//獲取焦點時，清空提示內容
		String temp = textField.getText();
		if(temp.equals(hintText)) {
			textField.setText("");
			textField.setForeground(Color.BLACK);
		}
		
	}

	@Override
	public void focusLost(FocusEvent e) {	
		//失去焦點時，沒有輸入內容，顯示提示內容
		String temp = textField.getText();
		if(temp.equals("")) {
			textField.setForeground(Color.GRAY);
			textField.setText(hintText);
		}
		
	}

}
 

JTextField jTextField = new JTextField();
jTextField.addFocusListener(new JTextFieldHintListener(jTextField, "提示內容"));