Java - 如何在 switch 语句中调用方法？答案

【问题标题】：Java - How do I call a method within a switch statement?Java - 如何在 switch 语句中调用方法？
【发布时间】：2019-10-04 07:35:25
【问题描述】：

averageLength 获取用户在前一种情况下输入的所有词，并获取平均词数。 switch 语句位于 main 方法下（此处未显示），但是当我尝试实现案例 3 以获得平均值时，它不起作用，因为average 未在main 方法下声明，它在averageLength 下。我怎样才能解决这个问题？谢谢

    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);

    }
}

【问题讨论】：

我在这段代码中看不到switch：我看到case 和default，但看不到语句从哪里开始。
average 是 main 方法中的局部变量。您不能在该方法之外使用它。一种解决方法是将其声明移到方法之外，在类主体中并使其成为static。
很难判断，因为您的代码不完整，但从 averageLength() 函数返回 average 的值可能会有所帮助
我已经上传了整个代码

标签： java variable-declaration

【解决方案1】：

您粘贴的代码存在一些问题 - 其中一些已在之前的 cmets/answers 中发现，但为了完整起见，我也会在此处列出：

averageLenth 名称中的错字 - 更改为 averageLength。因此，您的代码将无法编译。
averageLength(String[] words, int count) 的签名在呼叫站点不被认可 - 在交换机内部的呼叫站点更改为 averageLength(words, count)。

averageLength 的实现不正确 - 您的实现实际上并没有遍历单词数组并计算平均值，而是似乎在询问扫描仪的下一个输入。我已经改变了下面代码中的实现，通过迭代单词数组来计算平均值。

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: ");
 }
}

【讨论】：

【解决方案2】：

从显示的代码中，您可以调用不带参数的“averageLength()”，而它需要两个参数：单词数组及其计数。

该调用还包含一个错字（“g”缺失）。

因此，编译器无法找到该函数，因为它引用了一个实际上并不存在的函数。

另外，在“averageLength()”的两个参数中，单词数组是未使用的，您重新扫描单词而不是使用通过开关的其他情况建立的列表。这可能是一个逻辑错误。

【讨论】：

【解决方案3】：

请修复：

在方法main(): averageLenth(); 到averageLength(words, count);
在方法averageLength()：double sum; 到double sum = 0;

【讨论】：

【解决方案4】：

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);

    }
}

【讨论】：