Java: StringBuilder setCharAt 无法正常工作

Question

所以我正在制作一个程序，其中每个字母的大小写都颠倒了。如果输入 "Hello"，它会输出 "hELLO"。我知道无论我在做什么都行不通，但我只是不完全清楚为什么它行不通。

  public static void main(String [] args){

  Scanner keyboard = new Scanner(System.in);
  keyboard.useDelimiter(System.getProperty("line.separator"));
  char letter;
  char newLetter;

  String strLetter;
  System.out.print("Phrase: ");
  String phrase = keyboard.next();
  StringBuilder aWord = new StringBuilder(phrase);
  int wordLength = phrase.length();

  //loop through each letter
  for (int x = 0; x < wordLength; x++) {
     letter = phrase.charAt(x);

     //if letter is uppercase, set newLetter to lowercase and vice versa.
     if (Character.isUpperCase(letter)) {
        newLetter = Character.toLowerCase(letter);
     } else {
        newLetter = Character.toUpperCase(letter);
     }
     //When I print new letter here, it shows as the updated version
     //However, setCharAt is not actually updating, as seen by 
     //the "System.out.print(phrase);" line outside of the loop.
     aWord.setCharAt(x,newLetter);
     System.out.print(newLetter);
  }

  System.out.println();
  System.out.print(phrase);
  }

Answer 1

它确实有效，但最后您在变量 phrase 中打印原始字符串，您可能想在变量 aWord.

中打印转换后的字符串

Java: StringBuilder setCharAt 无法正常工作

Java: StringBuilder setCharAt not working properly

java

stringbuilder