java - 循环和逻辑语句

Question

我有这个类(class)所需的程序，他们要求我完成它的方式让我很困惑，因为我无法输出正确的答案。需要的是一系列输入，其中包含一系列“x”、“X”和“r”，它们依次输出声音。如果输入包含不是“x”、“X”或“r”的字符，则必须输出类似于“请输入有效输入”的内容。在大多数情况下，我已经把所有东西都放下了，但我无法找到一种方法来正确显示无效的输入字符串。

import java.util.Scanner; 
public class String2Beat { //main class
public static void main(String[] args) { 
    Scanner scan = new Scanner(System.in); 
    System.out.println("To play a drum song please enter a series of x's and r's."); 
    System.out.println("Use an Uppercase X for the base drum, "); 
    System.out.println("Use a Lowercase x for the snare drum, "); 
    System.out.println("Or use a Uppercase R for a rest:"); 
    String drums = scan.nextLine(); 

    for (int j = 0; j < 3; j++){
        for (int i = 0; i < drums.length(); i++){
            if (drums.charAt(i) != 'x' && drums.charAt(i) != 'X' && drums.charAt(i) != 'r'){
                System.out.println("not a valid string input");
            }
            else {
                if (drums.charAt(i) == 'X'){
                    System.out.println("Now playing a Bass Drum. " + drums.charAt(i)); 
                    playBass(); 
                }
                else if(drums.charAt(i) == 'x'){
                    System.out.println("Now playing a Snare Drum. " + drums.charAt(i)); 
                    playSnare(); 
                }
                else if(drums.charAt(i) == 'r'){
                    System.out.println("Now playing a Rest. " + drums.charAt(i)); 
                    playRest(); 
                }
            }

        }

    }

    scan.close();
}

Answer 1

您需要做的是在播放声音之前确定字符串是否包含无效输入。您的程序可能应该如下所示:

import java.util.Scanner; 
public class String2Beat { //main class
public static void main(String[] args) { 
    Scanner scan = new Scanner(System.in); 
    System.out.println("To play a drum song please enter a series of x's and r's."); 
    System.out.println("Use an Uppercase X for the base drum, "); 
    System.out.println("Use a Lowercase x for the snare drum, "); 
    System.out.println("Or use a Uppercase R for a rest:"); 
    String drums = scan.nextLine(); 

    boolean test = false;

    for (int i = 0; i < drums.length(); i++)
    {
        if (drums.charAt(i) != 'X' || drums.charAt(i) != 'x' || drums.charAt(i) != 'R')
            test = true;
    }

    if (!test)
    {
        for (int j = 0; j < 3; j++)
        {
            for (int i = 0; i < drums.length(); i++)
            {
                    if (drums.charAt(i) == 'X')
                    {
                        System.out.println("Now playing a Bass Drum. " + drums.charAt(i)); 
                        playBass(); 
                    }
                    else if(drums.charAt(i) == 'x')
                    {
                        System.out.println("Now playing a Snare Drum. " + drums.charAt(i)); 
                        playSnare(); 
                    }
                    else
                    {
                        System.out.println("Now playing a Rest. " + drums.charAt(i)); 
                        playRest(); 
                    }
                }
            }
        }
    }
    else
    {
        System.out.println("not a valid string input");
    }

    scan.close();
}