import java.util.Random;public class StringUtil {    private static final int Num_WORD = 1;//数字    private static final int STR_WORD = 2;//字母    private static final int STR_NUM_WORD = 3;//字母数字    private static final int MIX_WORD = 4;//字母数字符号    /**     * 获取随机字符串     * @param style  输出格式  1纯数字，2纯字符串，3字符数字组合，4字符数字符号组合。     * @param length 输出长度     * */    public static String getRandomStr(int style, int length) {         if (style == Num_WORD) {                return getNumRandom(length);            } else if (style == STR_WORD) {                return getStrRandom(length);            } else if (style == STR_NUM_WORD) {                return getStrNumRandom(length);            }else if (style == MIX_WORD) {                return getMixRandom(length);            }else{                 return getMixRandom(length);             }         }    //纯数字    private static String getNumRandom(int length) {        int[] array = new int[length];        StringBuilder str = new StringBuilder();        for (int i = 0; i < length; i++) {            array[i] = (int) (Math.random() * 10);            str.append(array[i]);        }        return str.toString();    }    //纯字母    private static String getStrRandom(int length) {        int[] array = new int[length];        char[] chars = new char[length];        StringBuilder str = new StringBuilder();        for (int i = 0; i < length; i++) {            while (true) {                array[i] = (int) (Math.random() * 1000);                if ((array[i] > 64 && array[i] < 91)                        || (array[i] > 96 && array[i] < 123))                    break;            }            chars[i] = (char) array[i];            str.append(chars[i]);        }        return str.toString();    }    //字母数字组合    public static String getStrNumRandom(Integer length) {          StringBuilder str = new StringBuilder();        Random random = new Random();          for (int i = 0; i < length; i++) {              boolean b = random.nextBoolean();              if (b) { // 字符串                  int choice = random.nextBoolean() ? 65 : 97; //取得65大写字母还是97小写字母                  str.append((char) (choice + random.nextInt(26)));// 取得大写字母              } else { // 数字                  str.append(random.nextInt(10));              }          }          return str.toString();      }          //字母数字符号组合    private static String getMixRandom(int length) {        int[] array = new int[length];        char[] chars = new char[length];        StringBuilder str = new StringBuilder();        for (int i = 0; i < length; i++) {            while (true) {                array[i] = (int) (Math.random() * 1000);                if (array[i] > 47 && array[i] < 91 || (array[i] > 96 && array[i] < 123))                    break;            }            chars[i] = (char) array[i];            str.append(chars[i]);        }        return str.toString();    }        public static void main(String[] args) {        System.out.println(StringUtil.getRandomStr(4, 10));    }}