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Question

我正在编写一个程序，我必须使用方法来计算我的字符串，.upper 和 lower 使用 switch 语句。我的代码没有显示任何错误，有人可以帮忙。

import java.util.*;
public class Strings
{

    public static void main(String[] args) 
    {
        String selection;

        Scanner keyboard = new Scanner(System.in);

        System.out.println("*********** EXAM 3 ENTER A STRING *************");
        System.out.println("Enter 1 to display the number of words in the string");
        System.out.println("Enter 2 to display the string in all capital letters");
        System.out.println("Enter 3 to display the string in all lower case letters");  
        System.out.println("Enter 4 to display the string in reverse order");
        System.out.println("Enter -1 to exit");
        selection = keyboard.nextLine();

        switch(selection.charAt(0))
        {
        case 1:
            numberOfWords(selection);
            break;
        case 2:
            allCapitals(selection);
            break;
        case 3:
            allLowers(selection);
            break;
        case 4:
            reverseOrder(selection);
            break;



        }//ends switch


    }

    /*public static void menuMethod(String [] args)
    {


        Scanner input = new Scanner(System.in);



        System.out.println("*********** EXAM 3 ENTER A STRING *************");
        System.out.println("Enter 1 to display the number of words in the string");
        System.out.println("Enter 2 to display the string in all capital letters");
        System.out.println("Enter 3 to display the string in all lower case letters");  
        System.out.println("Enter 4 to display the string in reverse order");
        System.out.println("Enter -1 to exit");



        }
       */







       public static void numberOfWords(String selection)
        {

          String input;  // To hold input


          Scanner keyboard = new Scanner(System.in);


          System.out.print("Enter a string: ");
          input = keyboard.nextLine();

          // Display the number of words.
          System.out.println("That string has " + wordCount(input) + " words in it.");



       }
       public static int wordCount(String str)
       {
          StringTokenizer strTok = new StringTokenizer(str);
          return strTok.countTokens();
       }


       public static void allCapitals (String str)
       {
        String input;
        String capInput;

        Scanner keyboard = new Scanner(System.in);

        System.out.println("Please enter a string. ");
        input = keyboard.nextLine();//You must use nextLine here next will not work.

        capInput = input.toUpperCase();
        System.out.println("Your capital case string = \n" + capInput); 
       }

       public static void allLowers (String str)
       {
        String input;
        String lowerInput;

        Scanner keyboard = new Scanner(System.in);

        System.out.println("Please enter a string. ");
        input = keyboard.nextLine();//You must use nextLine here next will not work.

        lowerInput = input.toUpperCase();
        System.out.println("Your lower case string = \n" + lowerInput); 
       }

       public static void reverseOrder (String str)
       {
          String input;  // To hold input


          Scanner keyboard = new Scanner(System.in);


          System.out.print("Enter something: ");
          input = keyboard.nextLine();

          // Display it backwards.
          backward(input);
       }


       public static void backward(String str)
       {
          for (int i = str.length() - 1; i >= 0; i--)
             System.out.print(str.charAt(i));
          System.out.println();
       }


}

Answer 1

请使用此代码进行切换

 switch(selection.charAt(0))

        {

        case '1':
            numberOfWords(selection);
            break;

        case '2':
            allCapitals(selection);
            break;

        case '3':
            allLowers(selection);
            break;

        case '4':
            reverseOrder(selection);
            break;

        }//ends switch

Answer 2

将您的开关条件替换为

switch(Integer.parseInt(selection))
{
//your code
}

而不是

switch(selection.charAt(0))
{
  //your code
}

如果您使用charAt(0)，您的检查条件必须是这样，因为该方法返回一个字符值

    case '1':
        numberOfWords(selection);
        break;
    case '2':
        allCapitals(selection);
        break;
    case '3':
        allLowers(selection);
        break;
    case '4':
        reverseOrder(selection);
        break;

Answer 3

你还没有说程序输出有什么问题。尽可能彻底地解释您的问题将帮助您快速得到一个好的答案。

至于可能出现的问题：

1. 您的allLowers() 方法正在使用toUpperCase()。作为一种良好的设计实践，尽量少复制粘贴代码，因为复制/粘贴代码意味着可能有一个函数可以做同样的事情。

2. 您实际上从未检查过-1 的输入。您在当前方法中要做的所有事情（如果要检查退出条件）就是检查 - 符号，因为它是第一个字符，而不是整个 -1 字符串，如果你扩展程序。