Java中随机数生成常见的几种方式及适用场景

import java.security.SecureRandom;
SecureRandom secureRandom = new SecureRandom();
int secureInt = secureRandom.nextInt(1000); // 生成0-999的加密安全随机数 [2,3](@ref)

// 生成6位数字（100000到999999）
int length = 6;
int number = random.nextInt((int) Math.pow(10, length)) + (int) Math.pow(10, length - 1); [2](@ref)

Random seededRandom = new Random(12345L); // 固定种子
int repeatableNum = seededRandom.nextInt(100); // 每次运行结果相同 [6](@ref)

import org.apache.commons.lang3.RandomUtils;
int num = RandomUtils.nextInt(1000, 10000); // 生成4位数验证码 [2](@ref)

char randomLower = (char) ('a' + Math.random() * 26);  
// 示例输出：'k'、'd'等

char randomUpper = (char) ('A' + Math.random() * 26);  
// 示例输出：'X'、'B'等

public static char getRandomChar(char start, char end) {
    return (char) (start + Math.random() * (end - start + 1));
}
// 示例：生成a-z之间的字母
char customChar = getRandomChar('a', 'z');

public static String generateLowerString(int length) {
    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < length; i++) {
        sb.append((char) ('a' + Math.random() * 26));
    }
    return sb.toString();
}
// 示例：generateLowerString(5) → "bqthm"

public static String generateMixedCaseString(int length) {
    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < length; i++) {
        // 随机选择大小写字母
        boolean isLower = Math.random() < 0.5;
        char base = isLower ? 'a' : 'A';
        sb.append((char) (base + Math.random() * 26));
    }
    return sb.toString();
}
// 示例：generateMixedCaseString(6) → "JxRkYf"

public static String generateAlphaNumeric(int length) {
    String chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < length; i++) {
        int index = (int) (Math.random() * chars.length());
        sb.append(chars.charAt(index));
    }
    return sb.toString();
}
// 示例：generateAlphaNumeric(8) → "3hF8kZ2p"