返回字符在字符串中出现的次数

Question

public class StringFind {

   /** findLetter looks for a letter in a String
    * @param String letter to look for
    * @param String text to look in
    * @return boolean true if letter is in text
    * After running the code, change this method to return
    * an int count of how many times letter is in the text.
    */
    public int findLetter(String letter, String text) {
        int count = 0;
        for(int i=0; i < text.length(); i++) {
            if (text.substring(i, i+1).equalsIgnoreCase(letter)) {         
                count = count++;
            }
        }
         
        return(count);
    }

    public static void main(String args[]) {
        StringFind test = new StringFind();
        String message = "Apples and Oranges";
        String letter = "p";
        System.out.println("Does " + message +  " contain a " + letter + "?");
    }
}

此代码有错误，我不确定如何修复它。 此代码应该返回字母在用户输入的消息中出现的次数。 我一直在努力弄清楚我需要毫无错误地改变什么。

Answer 1

第一个错误是在你有的findLetter中

count = count++; // this is effectively count = count;

那应该是

count++; // or count = count + 1;

那你就不会打电话给findLetter 。 将您当前的println更改为类似

System.out.printf("%s contains %s %d times.%n", message, letter, 
        test.findLetter(letter, message));

没有其他变化，然后我得到

Apples and Oranges contains p 2 times.

Answer 2

要完成 Elliott Frisch 给出的答案，您的 function 的第一个参数错误，它是一个字符而不是字符串，鉴于此，您需要使用 function charAt 来更改在字符串中查找字符的方式，使其成为更简单（ https://www.w3schools.com/java/ref_string_charat.asp ）。 这不是强制性的改变，但我认为它更有意义。

public class StringFind {
    /** findLetter looks for a letter in a String
     * @param String letter to look for
     * @param String text to look in
     * @return boolean true if letter is in text
     * After running the code, change this method to return
     * an int count of how many times letter is in the text.
     */
    public int findLetter(char letter, String text)
    {
        int count = 0;
        for(int i=0; i < text.length(); i++)
        {    if(text.charAt(i) == letter)
            count++;
        }


        return(count);

    }

    public static void main(String args[])
    {
        StringFind test = new StringFind();
        String message = "Apples and Oranges";
        Character letter = 'p';
        System.out.printf("%s contains %s %d times.%n", message, letter, test.findLetter(letter, message));
    }
}