"计算字符串中的字符出现次数 - Java"

Question

我在编写一个采用字符串并计算第一个字符（或实际上任何字符）出现的次数的方法时遇到问题。 我编写的代码如下，但由于某种原因，当我运行它时，它总是返回正确计数的一半。 任何帮助将不胜感激，谢谢。

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

你递增i两次，每次迭代中，所以你跳过半个汉字：

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

你当前的问题是i++; 每次迭代发生两次。

另一种方法是使用

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

它给出了"x"出现在s 。 可以说它不是最有效的方式，但很明显。

Answer 3

i ++ for for循环将i值递增1，无需在eloop内递增

在这里检查For循环的工作

  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);