"計算字符串中的字符出現次數 - Java"

Question

我在編寫一個采用字符串並計算第一個字符（或實際上任何字符）出現的次數的方法時遇到問題。 我編寫的代碼如下，但由於某種原因，當我運行它時，它總是返回正確計數的一半。 任何幫助將不勝感激，謝謝。

public static void countOccurrences(String string1) {
    int counter = 0;
    char toCheck = string1.charAt(0);
    char compareChar;
    for (int i = 0; i < string1.length(); i++) {
        compareChar = string1.charAt(i);
        if (toCheck == compareChar) {
            counter++;
        }
        i++;
    }
    System.out.println(toCheck + " appears " + counter + " times in string1.");
}

Answer 1

你遞增i兩次，每次迭代中，所以你跳過半個漢字：

for (int i = 0; i < string1.length(); i++) { // i is incremented here

  compareChar = string1.charAt(i);
  if (toCheck == compareChar){
      counter++ ;
  }
  i++ ; // i is incremented again here - remove this line

}

Answer 2

你當前的問題是i++; 每次迭代發生兩次。

另一種方法是使用

s.length() - s.replace("x", "").length()

它給出了"x"出現在s 。 可以說它不是最有效的方式，但很明顯。

Answer 3

i ++ for for循環將i值遞增1，無需在eloop內遞增

在這里檢查For循環的工作

  public static void countOccurrences(String string1) {

  int counter = 0;

  char toCheck = string1.charAt(0);

  char compareChar;

  for (int i = 0; i < string1.length(); i++) { 

      compareChar = string1.charAt(i);
      if (toCheck == compareChar){
          counter++ ;
      }
  }
  System.out.println(toCheck + " appears " + counter + " times in string1.");
}

Answer 4

    /* Most common string occurrence related solutions using java 8 */
    
    //find all character occurrences in a string
    String myString = "test";
    List<Character> list = myString.chars().mapToObj(c -> (char)c).collect(Collectors.toList());
    list.stream().distinct().forEach(c -> System.out.println(c + " = " + Collections.frequency(list, c)));

    //find one specific character occurrence in a string
    String myString = "test";
    char search = 't';
    long count = myString.chars().filter(c -> c == search).count();
    System.out.println(count);

    //find all unique characters in a string
    String myString = "test";
    List<Character> list = myString.chars().mapToObj(c -> (char)c).collect(Collectors.toList());
    list.stream().filter(c -> Collections.frequency(list,c) == 1).forEach(System.out::println);

    //find first unique character in a string
    String myString = "test";
    List<Character> list = myString.chars().mapToObj(c -> (char)c).collect(Collectors.toList());
    char firstUniqueChar = list.stream().filter(c -> Collections.frequency(list,c) == 1).findFirst().get();
    System.out.println(firstUniqueChar);