恩,还没有写完,只是代码的一不分. 不过我会努力的!

import javax.swing.*;
import java.awt.*;
public class customer
{
   public static void main(String args[])
      {
         JFrame frameobj;
         JPanel panelobj;
         JLabel Labelobj_1,Labelobj_2;
         JTextField textobj;
         JComboBox Listobj;

         GridBagLayout Girdobj;
         GridBagconstraints constraintsobj;

        frameobj=new JFrame("聊天室");
        panelobj=new JPanel();

        frameobj.getContentPane().add(panelobj);
        frameobj.setDefaultCloseOperation(frameobj.EXIT_ON_CLOSE);
        
        Labelobj_1=new JLabel("请输入你的用户名:");
        Labelobj_1.setBackground(Color.green);
        constraintsobj.gridx=0;
        constraintsobj.gridy=0;
        constraintsobj.anchor=GridBayConstraints.NORTHWEST;
        constraintsobj.fill=GridBayConstraints.BOTH;
        Girdobj.setConstraints(Labelobj_1,constraintsobj);
        panelobj.add(Labelobj_1);

        textobj=new JTextField(5);
        textobj.setBackground(Color.white);
        constraintsobj.gridx=0;
        constraintsobj.gridy=1;
        Gridobj.gridwidth=GridBagConstraints.REMAINDER;
        Gridobj.setConstraints(textobj,constraintsobj);
        panelobj.add(textobj);
       

        Labelobj_2=new JLabel("请选择你所在的城市:");
        panelobj.add(Labelobj_2); 
        constraintsobj.gridx=1;
        constraintsobj.gridy=2;
        Girdobj.setConstraints(Labelobj_2,constraintsobj);
        panelobj.add(Labelobj_2);
        
        String city[]={"china","Ameriaca","Japne"};
        Listobj=new JComboBox(city);
        panelobj.add(Listobj);
        constraintsobj.gridx=1;
        constraintsobj.gridy=1;
        constraintsobj.anchor=GridBayConstraints.NORTHWEST;
        Girdobj.setConstraints(Listobj,constraintsobj);
        panelobj.add(Listobj);
        
        frameobj.setVisible(true);
        frameobj.setSize(449,475);
      }
}