Java生成指定长度的随机数

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char[] str = {'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'};int[] num = {1, 2, 3, 4, 5, 6, 7, 8, 9};String ALLCHAR = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";

@Test
public void getRamdonString() { final int maxNum = 36;
int i; // 生成的随机数
int count = 0; // 生成的密码的长度 char[] str = {'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'};
StringBuffer pwd = new StringBuffer("");
Random r = new Random();
while (count < maxNum) {
// 生成随机数，取绝对值，防止生成负数，
i = Math.abs(r.nextInt(50)); // 生成的数最大为36-1
if (i >= 0 && i < str.length) {
pwd.append(str[i]);
count++;
}
}
System.out.println(pwd);
} @Test
public void getRamdonString2() {
StringBuffer sb = new StringBuffer();
String ALLCHAR = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
Random random = new Random();
for (int i = 0; i < 20; i++) {
sb.append(ALLCHAR.charAt(random.nextInt(ALLCHAR.length())));
} System.out.println(sb.toString());
}