java - 如何在不使用 .replace 的情况下替换 Java 中字符串中的字符？

Question

该程序的目标是提示用户输入单个字符和一个短语，然后用“$”替换该短语中该字符的所有实例。我下面的程序就是这样做的，但是当我把它展示给我的教授时，我被告知我不能在我构建的方法中使用 .replace，所以我必须想办法不使用它。我已经研究了一段时间，到目前为止我知道我可以用 for 循环替换它，但经过几次令人沮丧的迭代后，我似乎无法正确处理。对不起，如果我的代码看起来很时髦，我仍然是一名入门级的 Java 学生，所以我仍在学习基础知识。我在下面的代码片段末尾提供了一个建议的解决方案。

public static char getKeyCharacter(String userInput) {

    char keyCharacter;
    Scanner inputStream = new Scanner(System.in);
    while(userInput.length() > 1) 
    {
        System.out.println("Please enter a SINGLE character to use as key: ");
        userInput = inputStream.nextLine();
    }
    keyCharacter = userInput.charAt(0);

    return keyCharacter;
}
public static String getString(String userResponse) {

    Scanner inputStream = new Scanner(System.in);
    String theString;
    while(userResponse.length() > 500) {
        System.out.println("Please enter a phrase or sentence >= 4 and <=500 characters: ");
        userResponse = inputStream.nextLine();
    }
    while(userResponse.length() < 4) {
        System.out.println("Please enter a phrase or sentence >= 4 and <=500 characters: ");
        userResponse = inputStream.nextLine();

    }

    theString = userResponse;
    return theString;

}
public static String maskCharacter(String theString, char keyCharacter){

    String maskedString = "";
    final char mask = '$';
    maskedString = maskedString + theString.replace(keyCharacter, mask);
    System.out.println("String with " + keyCharacter + " masked: ");
    return maskedString;
}

public static String removeCharacter(String theString, char keyCharacter) {

    String modifiedString = " ";
    final char replaceChar = ' ';
    modifiedString = modifiedString + theString.replace(keyCharacter, replaceChar);
    System.out.println("String with " + keyCharacter + " removed:");
    return modifiedString;

}

public static int countKey(String theString, char keyCharacter) {
    int charCount = 0;
    for (int c = 0; c < theString.length(); c++) {
        if (theString.charAt(c) == keyCharacter) {
            charCount++;
        }
    }
    System.out.println("Occurences of " + keyCharacter + " in string:");
    return charCount;
}  

我相信解决方案看起来像这样，但到目前为止我一直没有成功 -

public static String maskCharacter(String theString, char keyCharacter){

    String maskedString = "";
    final char mask = '$';
    for (int k = 0; k < theString.length(); k++) {
        if (theString.charAt(k) == keyCharacter) {
            keyCharacter = mask;
         }
    System.out.println("String with " + keyCharacter + " masked: ");
    return maskedString;
}

我的问题在于使 maskedString = theString 的所有 keyCharacter 都被掩码替换。郑重声明，我还没有了解那些奇特的数组，所以如果有办法使用简单的 for 循环来做到这一点，我将不胜感激。提前感谢您的帮助!

Answer 1

我会使用 StringBuilder 和 String#toCharArray() 以及一个简单的 for-each 循环。喜欢，

public static String maskCharacter(String theString, char keyCharacter){
    StringBuilder sb = new StringBuilder();
    for (char ch : theString.toCharArray()) {
        if (ch == keyCharacter) {
            sb.append('$'); // <-- mask keyCharacter(s).
        } else {
            sb.append(ch); // <-- it isn't the character to mask
        }
    }
    return sb.toString();
}