int n = (int)(Math.random()*x);

Random random = new Random();
int n = random.nextInt(50)；

import java.awt.EventQueue;
import java.awt.Font;
import java.awt.List;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.util.ArrayList;
import java.util.Random;

import javax.swing.JDesktopPane;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JTextArea;
import javax.swing.JTextField;
import javax.swing.JButton;

public class Lottery extends JFrame {
 static JTextField textField;
 static JTextField textField_1;

 public static void main(String[] args) {

 EventQueue.invokeLater(new Runnable() {
  public void run() {
  try {
   Lottery frame = new Lottery();
   frame.setVisible(true);
  } catch (Exception e) {
   e.printStackTrace();
  }
  }
 });

 }

 public Lottery() {
 Font fn = new Font("宋體",Font.BOLD,15);//定義字體，并用構(gòu)造方法初始化
 setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);//定義窗口可關(guān)閉
 setBounds(100, 100, 625, 328);//窗口大小和位置
 getContentPane().setLayout(null);//絕對(duì)布局

 JDesktopPane desktopPane = new JDesktopPane();//定義小窗口
 //desktopPane.setToolTipText("輸入觀眾姓名按回車");
 desktopPane.setBounds(24, 12, 171, 286);
 getContentPane().add(desktopPane);//添加界面

 JLabel lblNewLabel = new JLabel("　　輸入觀眾姓名按回車");//為上面的小窗口定義標(biāo)簽名稱
 lblNewLabel.setBounds(0, 12, 171, 13);
 desktopPane.add(lblNewLabel);

 textField = new JTextField();//文本框
 textField.setBounds(10, 37, 149, 26);
 desktopPane.add(textField);
 textField.setColumns(30);

 List list = new List();//列表定義，用于存儲(chǔ)姓名
 desktopPane.setLayer(list, 100);
 list.setMultipleSelections(true);
 list.setBounds(8, 69, 151, 169);
 desktopPane.add(list);

 JDesktopPane desktopPane_1 = new JDesktopPane();
 desktopPane_1.setBounds(216, 12, 317, 286);
 getContentPane().add(desktopPane_1);

 JLabel lblNewLabel_1 = new JLabel("抽取觀眾成員");
 lblNewLabel_1.setBounds(12, 12, 220, 19);
 desktopPane_1.add(lblNewLabel_1);

 JLabel label = new JLabel("本次抽取的觀眾成員為");
 label.setBounds(12, 32, 275, 27);
 desktopPane_1.add(label);

 JTextArea textArea = new JTextArea(3,20);
 textArea.setBounds(12, 82, 281, 192);
 desktopPane_1.add(textArea);
 textArea.setFont(fn);

 JButton btnNewButton = new JButton("抽取");
 btnNewButton.setBounds(543, 218, 70, 23);
 getContentPane().add(btnNewButton);

 int i=0;
 ArrayList<String> str = new ArrayList<String>(); 
 textField.addKeyListener(new KeyListener() {//文本框鍵盤監(jiān)聽(tīng)
  public void keyTyped(KeyEvent e) {}
  public void keyReleased(KeyEvent e) {}
  public void keyPressed(KeyEvent e) {//當(dāng)出現(xiàn)回車按鍵時(shí)間，會(huì)處理文本框的字符串，將他們進(jìn)行儲(chǔ)存，添加到列表
  if(e.getKeyChar()!='\n')
   return ;
  String name = textField.getText();
  if(name.isEmpty())
   return ;
  list.add(name+"\n");
  str.add(name);
  textField.setText("");
  }
 });

 btnNewButton.addActionListener(new ActionListener() {//按鈕監(jiān)聽(tīng)，輸出隨機(jī)生成的標(biāo)號(hào)在字符串?dāng)?shù)組中的所對(duì)應(yīng)下標(biāo)的名字
  public void actionPerformed(ActionEvent e) {
  // TODO 自動(dòng)生成的方法存根
  int n = str.size();
  int x = (int) (Math.random()*n);
  String s0 = str.get(x);
  String s1 = "\t\t\t"+s0+"\n恭喜"+s0+"成為本次觀眾抽獎(jiǎng)的大獎(jiǎng)得主。"+"\n\n我們將為"+s0+"頒發(fā)：\n\t\t過(guò)期酸奶66箱。";
  textArea.setText(s1);
  }
 });
 }
}