简易聊天界面

package Layout;

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.HashMap;
import java.util.Map;

import javax.swing.*;

public class ChatInterface extends JFrame implements ActionListener {
    private JTextArea jta = new JTextArea();
    private JPanel jp = new JPanel();
    private Map<String, String> map = new HashMap();
    private String str[] = { "one", "two", "three", "four" };
    @SuppressWarnings("unused")
    private String str1[] = { str + "five" };
    private JComboBox jcb = new JComboBox(str);
    private JTextField jtf = new JTextField(10);
    private JButton b = new JButton("发送");
    private JScrollPane jsp = new JScrollPane(jta);//滚动条

    public ChatInterface() {
        map.put("one", "one");
        map.put("two", "two");
        map.put("three", "three");
        jp.add(jcb);
        jp.add(jtf);
        jp.add(b);
        // this.setLayout( new GridLayout(2,1));

        this.add(jp, BorderLayout.SOUTH);
        this.add(jsp, BorderLayout.CENTER);
        this.setTitle("聊天窗口");
        this.setIconImage((new ImageIcon("photo/psb.jpg")).getImage());
        this.setSize(500, 400);
        this.setLocation(100, 100);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setVisible(true);

        b.addActionListener(this);
        ActionEvent e = null;

        actionPerformed(e);

        // jta.append();
        // jta.append(getName());
        // System.out.println(str1);
        // if(b!=null){str.}
    }

    public static void main(String[] args) {
        ChatInterface l = new ChatInterface();

    }

    @Override
    public void actionPerformed(ActionEvent e) {
     try{
        String cmd = e.getActionCommand();
        if ("发送" == cmd) {
            jta.append(jtf.getText()+'
');}
        }catch( java.lang.NullPointerException a){}
        }
    }