java - 如何在没有任何复杂路由的情况下更改字符串？

Question

这是我为了完成我的其他项目而创建的代码。我已经尝试了一段时间，并且我认为如果循环中声明的变量太多，则不会访问循环中的深度，因此我认为我无法通过任何简单的方法来完成此操作。如果有人能告诉我为什么这段代码没有给我我希望的结果，那将会非常有帮助。

        char letter, D;
        int lengthString, position, positionInCat, textLength, repetitions;
        String cat = "cat", newCat = "", text, reversingText, reversedText = ""; //Goal: change "cat" to "cad"

        D = 'D';
        lengthString = cat.length();
        position = 0;
        positionInCat = 2; // what I am looking to alter. For example
        //position in cat = 2. 2 becomes a D or any other character. The output should //be: cDt

        reversingText = cat;
        repetitions = reversingText.length();
        textLength = reversingText.length() - 1;

        while  (repetitions > 0) { // reverses the text
                letter = reversingText.charAt(textLength);
                reversedText = reversedText + letter;
                repetitions--;
                textLength --;
        }
        letter = ' ';
        cat = reversedText;     // applies the reversion
        while (lengthString > 1) {
            while (lengthString != positionInCat) { // changes cat to what I want the outcome to be: cDt
            letter = cat.charAt(position);
            newCat = newCat + letter;   // rebuilding CAT
            position++;
            lengthString--;
            } 
            newCat = newCat + D;   // Altering the cat
            position++;
            lengthString--;
            while (lengthString > 0) {
                letter = cat.charAt(position);
                newCat = newCat + letter;
                position++;
                lengthString--; 
            } }
            letter = ' ';
            cat = newCat;
            reversingText = cat;    // giving the reversingText its work
            repetitions = reversingText.length();
            textLength = reversingText.length() - 1;

            while  (repetitions > 0) { // unreverses the reversed text
                    letter = reversingText.charAt(textLength);
                    reversedText = reversedText + letter;
                    repetitions--;
                    textLength --; 
            }
            cat = reversedText; // applies the reversion    

        System.out.print(cat); // what my work should have given me is cDt







  }

} // This is my attempt at it, but I can only get out "taccDt" with it, instead of "cDt"

Answer 1

Java 为您提供内置 String操纵方法。

改cat至 cDt您可以使用 StringBuilder .如果您知道索引，则 StringBuilder 可以轻松帮助您替换字符串中的单个字符。

StringBuilder stringBuilder = new StringBuilder("cat");
stringBuilder.setCharAt(1, 'D');
System.out.println(stringBuilder.toString()); //Prints cDt 

由于索引是基于 0 的，因此第一个字符 'c' 位于索引 0 处，第二个字符 'a' 位于索引 1 处。