如何使用Java编程生成一个包含大写字母、小写字母和数字的8位随机字符串？

在Java中，可以使用`java.util.Random`类和`StringBuilder`类结合的方式来生成一个包含大写字母、小写字母和数字的8位随机字符串。以下是一个简单的示例：

import java.security.SecureRandom;
import java.util.Random;

public class RandomStringGenerator {
    private static final String CHAR_LOWER = "abcdefghijklmnopqrstuvwxyz";
    private static final String CHAR_UPPER = CHAR_LOWER.toUpperCase();
    private static final String NUMBER = "0123456789";

    public static String generateRandomString(int length) {
        StringBuilder sb = new StringBuilder(length);
        Random random = new SecureRandom(); // 使用SecureRandom获得更安全的随机数

        // 遍历并添加大写字母、小写字母和数字字符到字符串
        for (int i = 0; i < length; i++) {
            int randomCharIndex;
            switch (random.nextInt(3)) { // 每次随机选择字母或数字
                case 0:
                    randomCharIndex = random.nextInt(CHAR_LOWER.length());
                    sb.append(CHAR_LOWER.charAt(randomCharIndex));
                    break;
                case 1:
                    randomCharIndex = random.nextInt(CHAR_UPPER.length());
                    sb.append(CHAR_UPPER.charAt(randomCharIndex));
                    break;
                case 2:
                    randomCharIndex = random.nextInt(NUMBER.length());
                    sb.append(NUMBER.charAt(randomCharIndex));
                    break;
            }
        }

        return sb.toString();
    }

    public static void main(String[] args) {
        String randomStr = generateRandomString(8); // 生成8位随机字符串
        System.out.println("Random string: " + randomStr);
    }
}