Java中随机长度数字字符串的生成与条件分组处理

int minLength = 25;
int maxLength = 50;
// 生成25到50之间的随机整数作为字符串长度
int randomLength = (int)(Math.random() * (maxLength - minLength + 1)) + minLength;

StringBuilder randomStringBuilder = new StringBuilder(); // 使用StringBuilder提高拼接效率
for (int i = 0; i < randomLength; i++) {
    int randomNumber = (int)(Math.random() * 10); // 生成0-9的随机数字
    randomStringBuilder.append(randomNumber);
}
String randomString = randomStringBuilder.toString();
System.out.println("生成的字符串长度: " + randomLength);
System.out.println("生成的字符串: " + randomString);

// 错误的尝试
for (int i = 0; i <= length; i++) {
   if (length > 30)
      System.out.println("Group: " + randomString.substring(i, 3)); // 错误：endIndex不应固定为3
   else
      System.out.println("Group: " + randomString.substring(i, 2)); // 错误：endIndex不应固定为2
}

// 确定分组步长
int groupStep;
if (randomLength > 30) {
    groupStep = 3;
} else {
    groupStep = 2;
}

System.out.println("分组步长: " + groupStep);

// 遍历字符串并进行分组
for (int i = 0; i < randomLength; i += groupStep) {
    // substring的结束索引是当前起始索引i加上步长groupStep
    // 但必须确保结束索引不超过字符串的总长度
    int endIndex = Math.min(randomLength, i + groupStep);
    String group = randomString.substring(i, endIndex);
    System.out.println("Group: " + group);
}

import java.io.IOException;

public class StringGroupingTutorial {

    /**
     * 生成一个指定长度范围内的随机数字字符串
     * @param minLength 最小长度
     * @param maxLength 最大长度
     * @return 生成的随机数字字符串
     */
    public static String generateRandomNumericString(int minLength, int maxLength) {
        int randomLength = (int)(Math.random() * (maxLength - minLength + 1)) + minLength;
        StringBuilder randomStringBuilder = new StringBuilder();
        for (int i = 0; i < randomLength; i++) {
            int randomNumber = (int)(Math.random() * 10);
            randomStringBuilder.append(randomNumber);
        }
        System.out.println("生成的字符串长度: " + randomLength);
        System.out.println("生成的字符串: " + randomStringBuilder.toString());
        return randomStringBuilder.toString();
    }

    public static void main(String[] args) {
        // 1. 生成随机数字字符串
        String generatedString = generateRandomNumericString(25, 50);
        int stringLength = generatedString.length();

        // 2. 根据字符串长度确定分组步长
        int groupStep;
        if (stringLength > 30) {
            groupStep = 3;
            System.out.println("字符串长度超过30，采用3位一组分组。");
        } else {
            groupStep = 2;
            System.out.println("字符串长度不超30，采用2位一组分组。");
        }

        // 3. 遍历字符串并进行分组
        System.out.println("\n--- 分组结果 ---");
        for (int i = 0; i < stringLength; i += groupStep) {
            // 计算子串的结束索引，确保不越界
            int endIndex = Math.min(stringLength, i + groupStep);
            String group = generatedString.substring(i, endIndex);
            System.out.println("Group: " + group);
        }
    }
}