Java生成随机密码

《Java编程的逻辑》

import java.util.Random;

public class RandomPwdV1 {

  /**
   * 生成随机密码：6位数字
   * 
   * @return 密码字符串
   */
  public static String randomPassword() {
    char[] chars = new char[6];
    Random rnd = new Random();
    for (int i = 0; i < 6; i++) {
      chars[i] = (char) ('0' + rnd.nextInt(10));
    }
    return new String(chars);
  }

  public static void main(String[] args) {
    System.out.println(randomPassword());
  }
}

import java.util.Random;

/**
 * 生成随机密码：简单8位
 * 对每个字符，先随机选类型，然后在给定类型中随机选字符
 */
public class RandomPwdV2 {
  private static final String SPECIAL_CHARS = "!@#3%&*_=+";

  private static char nextChar(Random rnd) {
    switch (rnd.nextInt(4)) {
      case 0:
        return (char) ('a' + rnd.nextInt(26));
      case 1:
        return (char) ('A' + rnd.nextInt(26));
      case 2:
        return (char) ('0' + rnd.nextInt(10));
      default:
        return SPECIAL_CHARS.charAt(rnd.nextInt(SPECIAL_CHARS.length()));
    }
  }

  /**
   * 生成随机密码：简单8位
   * 
   * @return
   */
  public static String randomPassword() {
    char[] chars = new char[8];
    Random rnd = new Random();
    for (int i = 0; i < 8; i++) {
      chars[i] = nextChar(rnd);
    }
    return new String(chars);
  }

  public static void main(String[] args) {
    System.out.println(randomPassword());
  }
}

import java.util.Random;

/**
 * 生成随机密码：复杂8位
 * nextIndex随机生成一个未赋值的位置，程序先随机生成4个不同类型的字符，放到随机位置上，然后给未赋值的其他位置随机生成字符。
 */
public class RandomPwdV3 {

  private static final String SPECIAL_CHARS = "!@#3%&*_=+";

  private static int nextIndex(char[] chars, Random rnd) {
    int index = rnd.nextInt(chars.length);
    while (chars[index] != 0) {
      index = rnd.nextInt(chars.length);
    }
    return index;
  }

  private static char nextSpecialChar(Random rnd) {
    return SPECIAL_CHARS.charAt(rnd.nextInt(SPECIAL_CHARS.length()));
  }

  private static char nextUpperlLetter(Random rnd) {
    return (char) ('A' + rnd.nextInt(26));
  }

  private static char nextLowerLetter(Random rnd) {
    return (char) ('a' + rnd.nextInt(26));
  }

  private static char nextNumLetter(Random rnd) {
    return (char) ('0' + rnd.nextInt(10));
  }

  private static char nextChar(Random rnd) {
    switch (rnd.nextInt(4)) {
      case 0:
        return (char) ('a' + rnd.nextInt(26));
      case 1:
        return (char) ('A' + rnd.nextInt(26));
      case 2:
        return (char) ('0' + rnd.nextInt(10));
      default:
        return SPECIAL_CHARS.charAt(rnd.nextInt(SPECIAL_CHARS.length()));
    }
  }

  /**
   * 生成随机密码：复杂8位
   * 
   * @return 密码字符串
   */
  public static String randomPassword() {
    char[] chars = new char[8];
    Random rnd = new Random();
    chars[nextIndex(chars, rnd)] = nextSpecialChar(rnd);
    chars[nextIndex(chars, rnd)] = nextUpperlLetter(rnd);
    chars[nextIndex(chars, rnd)] = nextLowerLetter(rnd);
    chars[nextIndex(chars, rnd)] = nextNumLetter(rnd);
    for (int i = 0; i < 8; i++) {
      if (chars[i] == 0) {
        chars[i] = nextChar(rnd);
      }
    }
    return new String(chars);
  }

  public static void main(String[] args) {
    System.out.println(randomPassword());
  }
}