java - 第二个循环背后的逻辑

Question

最近，我被要求完成一项作业，即编写一个简单的 Java 应用程序，该应用程序将电话号码作为字符串读取，并打印出电话号码中每个数字的频率。然而，在与我的伙伴仔细查看后，我对为什么需要第二个循环行感到有些困惑，代码如下

public class CharacterFrequency {

public static Scanner kbd = new Scanner(System.in);

public static int MAXSIZE=10; //Constant for array size and easy change

public static void main(String[] args) {

    int telephoneNumArrayIndex = 0; //index where array will start checking
    char [] telephoneNumArray = new char[MAXSIZE]; //array holding tel Number digits.

    String telephoneNumber;//string that will that will read input from user.

    System.out.print("Please Enter a 10-digit Telephone Number: ");
    telephoneNumber = kbd.next();

    System.out.println("\nThe Following is the Number of Times Each Digit Appears:\n");

    //loop that will check and test  array for digits and ignore "white space" 
    //characters (-,*,., ,etc)
    for (int i = 0; i < telephoneNumber.length(); i++) {
        if (telephoneNumber.charAt(i) >= (char) 48
                && telephoneNumber.charAt(i) <= (char) 57) {
            telephoneNumArray[telephoneNumArrayIndex++] = telephoneNumber.charAt(i);
        }
    }

    //reasoning behind the loop. ??????
    int[] counter = new int[MAXSIZE];
    //loop to fill 
    for (int i = 0; i < counter.length; i++) {
        counter[i] = 0;
        System.out.println(counter[i]);
    }

    //loop that stores the frequency of each digit 0-9 to its corresponding array 
    //index. the char is then parsed to convert to int datatype in order to use the counter
    //in the array.
    for (int i = 0; i < telephoneNumArray.length; i++) {
        for (int j = 0; j < 10; j++) {
            if (telephoneNumArray[i] == (char) (j + 48)) {
                counter[j]++;
            }
        }
    }

    //loop that will display the frequency (counter[i]) of each digit (i),
    //used in a typical U.S. phone number by looping through each index of the array
    //and printing the number corresponding to that count from 0-9 

    for (int i = 0; i < telephoneNumArray.length; i++) {
        System.out.println(i + " - " + counter[i]);
    }


}

}

两种方式的结果都是相同的，但想知道它是否更有效？

Answer 1

第二个循环的目的是将计数器数组中的所有值初始化为 0。然而在 Java 中，基元数组的每个元素都初始化为其默认值。 int 的默认值为 0，因此计数器数组已将所有内容设置为 0。因此该循环毫无意义，可以删除。