Java获取ip地址

import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.net.InetAddress;
import java.net.UnknownHostException;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class ip extends JFrame
  implements ActionListener
{
  private static final long serialVersionUID = 3339481369781127417L;
  JButton jb1;
  JButton jb2;
  JButton jb3;
  JPanel jp;
  JLabel jl;
  JLabel jl1;
  JTextField jt;

  public ip()
  {
    this.jp = new JPanel();
    this.jl = new JLabel();
    this.jl1 = new JLabel("您的域名：");
    this.jb1 = new JButton("提交");
    this.jb2 = new JButton("重置");
    this.jb3 = new JButton("退出");
    this.jt = new JTextField(20);
    this.jb1.addActionListener(this);
    this.jb2.addActionListener(this);
    this.jb3.addActionListener(this);
    this.jp.setLayout(new GridLayout(3, 2));
    this.jp.add(this.jl1);
    this.jp.add(this.jt);
    this.jp.add(this.jb1);
    this.jp.add(this.jl);
    this.jp.add(this.jb2);
    this.jp.add(this.jb3);

    setBounds(200, 200, 500, 240);
    add(this.jp);
    setVisible(true);
    setDefaultCloseOperation(3);
  }

  public static void main(String[] args)
  {
    new ip();
  }

  public void actionPerformed(ActionEvent e) {
    if (e.getSource() == this.jb1) {
      String url = this.jt.getText();
      InetAddress ip = null;
      try {
        ip = InetAddress.getByName(url);
      }
      catch (UnknownHostException e1) {
        e1.printStackTrace();
      }
      this.jl.setText(ip.toString());
    }
    else if (e.getSource() == this.jb2) {
      this.jl.setText("");
      this.jt.setText("");
    } else {
      System.exit(0);
    }
  }
}