Java AWT在Panel中放置Textfield失败

Question

我在Java awt中用我的简单形式提交了一个特殊文本的奇怪问题。我的代码和结果如下：

import java.awt.GridLayout;
import java.awt.Label;
import java.awt.Panel;
import java.awt.TextField;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Frame;

public class GUI extends Frame {

public static TextField user        = null;
public static TextField password    = null;
public static TextField base        = null;

Label userLabel     = null;
Label passwordLabel = null;
Label baseLabel     = null;

public GUI(){
    this.setSize(260, 160);
    this.setTitle("Sybase connection");
    this.setResizable(false);
    //CLOSE OP
    this.addWindowListener(new WindowAdapter(){
        public void windowClosing( WindowEvent we){
            System.exit(0);
        }
    });
    //LAYOUT
    this.setLayout(null);

    // FORM PANEL
    Panel form = new Panel();
    form.setLayout(null);
    form.setBackground(new Color(0, 255, 0));
    form.setBounds(30,30, 200, 110);


    //TEXT/LABEl

    userLabel = new Label("User:");
    userLabel.setBounds(5, 5, 90, 20);
    form.add(userLabel);

    passwordLabel = new Label("Password:");
    passwordLabel.setBounds(5, 30, 90, 20);
    form.add(passwordLabel);

    baseLabel = new Label("Base:");
    baseLabel.setBounds(5, 55, 90, 20);
    form.add(baseLabel);

    user = new TextField(20);
    user.setBounds(100, 5, 90, 20);
    form.add(user);

    password = new TextField(20);
    password.setBounds(100, 30, 90, 20);
    form.add(password);

    base = new TextField(20);
    user.setBounds(100, 55, 90, 20);
    form.add(base);

    this.add(form);
    //TEXT/LABEL

    //BUTTON
    //LoginButton b = new LoginButton();

    //this.add(b);
    //BUTTON
}
public static void main(String[] args) {
    GUI frame = new GUI();
    frame.setVisible(true);
}

}

结果： enter image description here

那个丑陋的绿色背景仅用于检查面板是否位于一个好位置。你可以看到，其他两个TextField都可以。你有什么想法，为什么第一个不在表格面板？