java生成一个由大写字母和数字组成的6位的随机字符串，并且字符串不重复

Question

java生成一个由大写字母和数字组成的6位随机字符串，并且字符串不重复，求代码。

Answer 1

public static char[] generate() {

    char[] letters = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J',
            'K', 'L', 'M', 'N', 'O', 'P','Q', 'R', 'S', 'T', 'U', 'V',
            'W', 'X', 'Y', 'Z','0','1','2','3','4','5','6','7','8','9'};
    boolean[] flags = new boolean[letters.length];
    char[] chs = new char[6];
    for (int i = 0; i < chs.length; i++) {
        int index;
        do {
            index = (int) (Math.random() * (letters.length));
        } while (flags[index]);// 判断生成的字符是否重复
        chs[i] = letters[index];
        flags[index] = true;
    }
    return chs;
}