如何在字符串中交替使用大写和小写字符？

public String alternateCase(String str) {
    StringBuilder result = new StringBuilder();
    for (int i = 0; i < str.length(); i++) {
        char c = str.charAt(i);
        if (i % 2 == 0) {
            result.append(Character.toUpperCase(c));
        } else {
            result.append(Character.toLowerCase(c));
        }
    }
    return result.toString();
}

public String alternateCase(String str) {
    char[] chars = str.toCharArray();
    for (int i = 0; i < chars.length; i++) {
        if (i % 2 == 0) {
            chars[i] = (char) (chars[i] & ~32);  // 转换为大写
        } else {
            chars[i] = (char) (chars[i] | 32);   // 转换为小写
        }
    }
    return new String(chars);
}

public String alternateCase(String str) {
    StringBuilder result = new StringBuilder();
    boolean isUpperCase = true;
    for (char c : str.toCharArray()) {
        if (isUpperCase) {
            result.append(Character.toUpperCase(c));
        } else {
            result.append(Character.toLowerCase(c));
        }
        isUpperCase = !isUpperCase;
    }
    return result.toString();
}