生成随机的数字和字母组合

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));
    }
}