public class User implements Serializable{    private String id;// 自增型ID    private String username;// 用户名    private String password;// 用户密码 }

/* 我是多行注释 */if (null != password ) {    return "ok";}

import java.io.*; /*** This class demonstrates documentation comments.* @author Ayan Amhed* @version 1.2*/public class SquareNum {   /**   * This method returns the square of num.   * This is a multiline description. You can use   * as many lines as you like.   * @param num The value to be squared.   * @return num squared.   */   public double square(double num) {      return num * num;   }   /**   * This method inputs a number from the user.   * @return The value input as a double.   * @exception IOException On input error.   * @see IOException   */   public double getNumber() throws IOException {      InputStreamReader isr = new InputStreamReader(System.in);      BufferedReader inData = new BufferedReader(isr);      String str;      str = inData.readLine();      return (new Double(str)).doubleValue();   }   /**   * This method demonstrates square().   * @param args Unused.   * @return Nothing.   * @exception IOException On input error.   * @see IOException   */   public static void main(String args[]) throws IOException   {      SquareNum ob = new SquareNum();      double val;      System.out.println("Enter value to be squared: ");      val = ob.getNumber();      val = ob.square(val);      System.out.println("Squared value is " + val);   }}