Java - 如何在 switch 语句中调用方法？

Question

averageLength gets all the words the user has entered in the previous case and gets the average amount of words. The switch statement sits under the main method (not shown here) but when I try to implement case 3 to get the average, it does not work because average is not declared under the main method, its under averageLength . How can I fix this? Thanks

    import java.util.Scanner;
    import java.util.Arrays;

    /**
     * Word Manager
     *
     * @author Harry
     */
    public class WordManager {

    /**
     * Adds the word to the next empty space in the array, if there is space.
     * Returns the new size of the array.
     */
    public static int add(String[] words, int count, String word) {

        if (count < words.length) {
            words[count] = word;
            count++;
        } else {
            System.out.println("The array is full");
        }
        return count;
    }

    /** Displays the words in the collection as a comma separated list. */
    public static void printList(String[] words, int count) { 
    }

    public static void averageLength(String[] words, int count) {
        Scanner sc = new Scanner(System.in);
        double average;
        double sum;

        while (sc.hasNext()) {
            String userInput = sc.next();

            double charNum = userInput.length();
            sum = charNum + sum;
            count++;

            if (count > 0) {
                average = sum / count;
                System.out.println("Average word length = " + average);

            }
        }

    }
    public static void main(String[] args ) {
        Scanner sc = new Scanner(System.in);
        String[] words = new String[20];
        int count = 0;
        String aWord;
        int choice;

        do {
            System.out.println("\t MENU:");
            System.out.println("1. Add a word");
            System.out.println("2. Display words:");
            System.out.println("3. Display average word length");
            System.out.println("4. Quit");
            System.out.println("Enter option: ");
            choice = sc.nextInt();
            System.out.println("choice = "+choice);

            switch (choice) {
                case 1: 
                    System.out.println("Add a word");
                    aWord = sc.next();
                    count = add(words, count, aWord);
                    break;

                case 2:
                    System.out.println("Display words");
                    System.out.println("We have an array of " + words.length + " integers: " + Arrays.toString(words));
                    break;

                case 3:
                    averageLenth();              
                    break;

                default:
                    System.out.println("Invalid responce");

            }
        } while (choice >= 0 && choice < 4);

    }
}

Answer 1

From the code shown, you call "averageLength()" with no parameters, whereas it requires two: the array of words and their count.

The call also contains a typo (the "g" is missing).

So, the function cannot be found by the compiler, since it references a function that doesn't actually exist.

Additionally, of the two parameters of "averageLength()", the array of words is unused, you rescan for words instead of using the list established through the other cases of the switch. This is probably a logic error.

Answer 2

Please, fix:

1. In method main() : averageLenth(); to averageLength(words, count);
2. In method averageLength() : double sum; to double sum = 0;

Answer 3

import java.util.Scanner;
import java.util.Arrays;

/**
 * Word Manager
 *
 * @author Harry
 */
public class WrodManager {

    /**
     * Adds the word to the next empty space in the array, if there is space.
     * Returns the new size of the array.
     */
    public static int add(String[] words, int count, String word) {

        if (count < words.length) {
            words[count] = word;
            count++;
        } else {
            System.out.println("The array is full");
        }
        return count;
    }

    /** Displays the words in the collection as a comma separated list. */
    public static void printList(String[] words, int count) {
    }

    public static void averageLength(String[] words, int count) {
        Scanner sc = new Scanner(System.in);
        double average;
        double sum = 0;

        while (sc.hasNext()) {
            String userInput = sc.next();

            double charNum = userInput.length();
            sum = charNum + sum;
            count++;

            if (count > 0) {
                average = sum / count;
                System.out.println("Average word length = " + average);

            }
        }

    }

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String[] words = new String[20];
        int count = 0;
        String aWord;
        int choice;

        do {
            System.out.println("\t MENU:");
            System.out.println("1. Add a word");
            System.out.println("2. Display words:");
            System.out.println("3. Display average word length");
            System.out.println("4. Quit");
            System.out.println("Enter option: ");
            choice = sc.nextInt();
            System.out.println("choice = " + choice);

            switch (choice) {
            case 1:
                System.out.println("Add a word");
                aWord = sc.next();
                count = add(words, count, aWord);
                break;

            case 2:
                System.out.println("Display words");
                System.out.println("We have an array of " + words.length + " integers: " + Arrays.toString(words));
                break;

            case 3:
                averageLength(words, count);
                break;

            default:
                System.out.println("Invalid responce");

            }
        } while (choice >= 0 && choice < 4);

    }
}

Answer 4

There are a few issues with the code you've pasted - some of which have already been identified in previous comments/answers, but I'll list them here as well for completeness:

1. Typo in the name of averageLenth - change to averageLength . Your code will not compile because of this.
2. The signature of averageLength(String[] words, int count) is not being honoured at the call site - change to averageLength(words, count) at the call site inside the switch.

3. The implementation of averageLength is incorrect - your implementation is not infact iterating over the array of words and computing the average but appears to be asking the scanner for the next input. I've changed the impelentation in the code below to comput the average by iterating over the word array.

    import java.util.Scanner; import java.util.Arrays; /** * Word Manager * * @author Harry */ public class WordManager { /** * Adds the word to the next empty space in the array, if there is space. * Returns the new size of the array. */ public static int add(String[] words, int count, String word) { if (count < words.length) { words[count] = word; count++; } else { System.out.println("The array is full"); } return count; } /** * Displays the words in the collection as a comma separated list. */ public static void printList(String[] words, int count) { } private static void averageLength(String[] words, int count) { int sum=0; for(int word =0; word < count; word++){ int wordLength = words[word].length(); sum += wordLength; } double averageWorldLength = sum/count; System.out.println("Average word length = " +averageWorldLength; } public static void main(String[] args) { Scanner sc = new Scanner(System.in); String[] words = new String[20]; int count = 0; String aWord; int choice; do { displayMenuOptions(); choice = sc.nextInt(); System.out.println("choice = " + choice); switch (choice) { case 1: System.out.println("Add a word"); aWord = sc.next(); count = add(words, count, aWord); break; case 2: System.out.println("Display words"); System.out.println("We have an array of " + words.length + " integers: " + Arrays.toString(words)); break; case 3: averageLength(words, count); break; default: System.out.println("Invalid responce"); } } while (choice >= 0 && choice < 4); } private static void displayMenuOptions() { System.out.println("\t MENU:"); System.out.println("1. Add a word"); System.out.println("2. Display words:"); System.out.println("3. Display average word length"); System.out.println("4. Quit"); System.out.println("Enter option: "); } }