重复字符串java中的特定字符

public static void findDuplicateChars(String str, char target) {
    int count = 0;
    for (int i = 0; i < str.length(); i++) {
        if (str.charAt(i) == target) {
            count++;
        }
    }
    if (count > 1) {
        System.out.println("字符 '" + target + "' 在字符串中重复出现了 " + count + " 次。");
    } else {
        System.out.println("字符 '" + target + "' 在字符串中没有重复出现。");
    }
}

public static String replaceDuplicateChars(String str, char oldChar, char newChar) {
    StringBuilder sb = new StringBuilder();
    int count = 0;
    for (int i = 0; i < str.length(); i++) {
        if (str.charAt(i) == oldChar) {
            count++;
            if (count > 1) {
                sb.append(newChar);
            } else {
                sb.append(oldChar);
            }
        } else {
            sb.append(str.charAt(i));
        }
    }
    return sb.toString();
}

public static int countDuplicateChars(String str, char target) {
    int count = 0;
    for (int i = 0; i < str.length(); i++) {
        if (str.charAt(i) == target) {
            count++;
        }
    }
    return count > 1 ? count : 0;
}