java从循环中获取数组元素

Question

我试图从数组中获取一个元素，并在以后的代码中使用它，但代码中有一些逻辑错误。我希望用户输入他或她需要清洁的日期，然后打印出清洁的日期。代码如下：

import java.util.Scanner;

public class arrayLoopTest {

    public static void main(String[] args) {
        Scanner scr = new Scanner(System.in);
        String[] days = { "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday" };

        int i = 0;
        while (true) {
            System.out.println("On what day should the cleaning be scheduled ? ");
            String schedule = scr.nextLine();

            for (i = 0; i < days.length; i++) {

                if (days[i].equals(schedule)) {

                    System.out.println("Cleaning scheduled for " + schedule);

                } else {
                    System.out.println("Invalid, You have to choose one of these days: \n " + days[i]);
                }
            }

        }
    }
}

控制台输出

On what day should the cleaning be scheduled ? 
Thursday
Invalid, You have to choose one of these days: 
Monday
Invalid, You have to choose one of these days: 
Tuesday
Invalid, You have to choose one of these days: 
Wednesday
Cleaning scheduled for Thursday
Invalid, You have to choose one of these days: 
Friday
Invalid, You have to choose one of these days: 
Saturday
Invalid, You have to choose one of these days: 
Sunday
On what day should the cleaning be scheduled ? 

Answer 1

在检查任何一天是否匹配时，您要检查它是否匹配day[i]，并立即打印结果（甚至在检查数组的其余部分是否匹配之前）

一种可能的解决方案是跟踪用户输入是否已将一天与布尔值匹配。试着这样做：

public static void main(String[] args) {
        Scanner scr = new Scanner(System.in);
        String[] days = {"Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday"};

        int i = 0;

        boolean validEntry;
        while (true) {

            validEntry = false;
            System.out.println("On what day should the cleaning be scheduled ? ");
            String schedule = scr.nextLine();

            for (i = 0; i < days.length; i++) {

                if (days[i].equals(schedule)) {
                    System.out.println("Cleaning scheduled for " + schedule);
                    validEntry = true;
                }
            }

            if (!validEntry) {
                System.out.println("Invalid, You have to choose one of these days: \n" + Arrays.toString(days));
            }
        }
    }

注意，我也改变了

System.out.println("Invalid, You have to choose one of these days: \n" + days[i]);

对这个

System.out.println("Invalid, You have to choose one of these days: \n " + Arrays.toString(days));

Answer 2

我认为逻辑错误在于，在循环数组时打印响应，所以它总是打印出“无效…”至少六次

相反，您可以在数组中循环，直到找到匹配项，然后根据是否找到匹配项打印响应：

        boolean scheduleIsValid = false;
        for (i = 0; i < days.length; i++) {
            if (days[i].equals(schedule)) {
                scheduleIsValid = true;
                break; // Leave the for loop, we've already found what we were looking for.
            }
        }

        if (scheduleIsValid) {
            System.out.println("Cleaning scheduled for " + schedule);
            break; // Leave the while loop.
        } else {
            System.out.println("Invalid, You have to choose one of these days: \n " + days);
        }

Answer 3

Java Arrays实用程序是你的选择。不用手动循环，你可以从数组中提取ArrayList，使用IndexOf找到你的一天

List listOfDays = Arrays.asList(days);
int dayIndex = listOfDays.IndexOf(schedule);

if (dayIndex >= 0)
{
    System.out.println("Cleaning scheduled for " + listOfDays[dayIndex]);
}
else
{
    System.out.println("Invalid " + schedule); // Perform error handling as you wish
}

资料来源：

http://www.tutorialspoint.com/java/util/arrays_aslist.htm

http://www.tutorialspoint.com/java/util/arraylist_indexof.htm

Answer 4

请注意，有更有效、更简单的方法可以从循环中获取数组元素，但这是一种简单的方法，初学者应该很容易遵循

您有一个很好的for循环，但是在检查整个数组以查看用户输入是否匹配数组中的任何值之前，您正在向用户打印文本。我做了一个名为dayIsValid的布尔值，检查用户输入的字符串是否为有效日期。如果日期有效，则会打印出所需的消息。请注意，只有在我查看整个数组后，才会打印此消息

我注意到的另一件事是，您试图打印字符串数组中的所有日期，但只打印了一天。为了解决这个问题，我在字符串数组中循环，打印出值。希望这个解释对你有所帮助。如果您有任何问题，请随时在下面发表评论

Scanner scr = new Scanner(System.in);
String[] days = { "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday" };
boolean continueLooping = true;
//be aware that this while loop will execute infinitely, unless you change continuelooping to false inside the while loop
while (continueLooping) {
    System.out.println("On what day should the cleaning be scheduled ? ");
    String dayScheduledForCleaning = scr.next();
    boolean dayIsValid = false;
    for (int i = 0; i < days.length; i++) {
        if (days[i].equalsIgnoreCase(dayScheduledForCleaning)) {
            System.out.println("Cleaning scheduled for " + dayScheduledForCleaning);
            dayIsValid = true;
            break;
        }
    }
    if(! dayIsValid) {
        System.out.println("Invalid, You have to choose one of these days:");
        for(int i = 0; i < days.length; i++)
            System.out.println(days[i]);
    }
}

Answer 5

试试这个：

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

public class ArrayLoopTest {
    public static void main(String[] args) {
        Scanner scr = new Scanner(System.in);
        String[] days = { "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "Sunday" };

        int i = 0;
        while (true) {
            System.out.println("On what day should the cleaning be scheduled ? ");
            String schedule = scr.nextLine();

            for (i = 0; i < days.length; i++) {

                if (days[i].equals(schedule)) {

                    System.out.println("Cleaning scheduled for " + schedule);
                    break;
                }
            }

            if (i == days.length){
                System.out.println("Invalid, You have to choose one of these days: \n " + Arrays.asList(days));             
            }

        }
    }
}

如果您担心性能，可以使用哈希集。如果你不知道如何使用，只需发送一条消息，我就会发布解决方案

Answer 6

一个非常简单的方法是添加另一个变量：

String savedVar = ""; 
....
if (days[i].equals(schedule)) {
            savedVar = schedule; //save your user input here
            System.out.println("Cleaning scheduled for " + schedule);

        } else {
            System.out.println("Invalid, You have to choose one of these days: \n " + days[i]);
        }

然后在以后的代码中使用savedVar