Question

我正在尝试创建一个程序，用于打印一周中每天的温度。我不知道为什么我的代码正在打印＆＃34; null＆＃34;而不是一周中的每一天。我之前从未见过这个错误（我在开始编程课程中）并且我无法在教科书中找到任何信息。到目前为止，这是我的代码......

import java.util.Scanner;
public class TempsInOneWeek {

public static void main(String[] args) {
    Scanner scnr = new Scanner (System.in);
    final int NUMBER_OF_DAYS = 7;
    String[] dayOfWeek = new String[NUMBER_OF_DAYS];
    int[] temp = new int [7]; //array of 7 temperatures for 7 days of the week
    int tempForDay = 0;
    int i = 0; //loop variable

    System.out.println("Enter the temperature for each day, beginning with Sunday.");

    for (i = 0; i <= temp.length; ++i) {
        temp[i] = scnr.nextInt();
        System.out.println(dayOfWeek[i] + "/'s temperature was: " + temp[i] + " degrees.");
    }

    dayOfWeek[i] = "Sunday";    
    dayOfWeek[i] = "Monday";
    dayOfWeek[i] = "Tuesday";
    dayOfWeek[i] = "Wednesday";
    dayOfWeek[i] = "Thursday";
    dayOfWeek[i] = "Friday";
    dayOfWeek[i] = "Saturday";

    temp[i] = scnr.nextInt();
    temp[i] = scnr.nextInt();
    temp[i] = scnr.nextInt();
    temp[i] = scnr.nextInt();
    temp[i] = scnr.nextInt();
    temp[i] = scnr.nextInt();
    temp[i] = scnr.nextInt();
}

显然阵列在错误的位置，但它现在不会影响输出，所以我想表明我至少在这里尝试。真的我唯一的问题是如何打印一周的日子。关于如何处理上面的两个数组，可能还有一点方向。

Answer 1

只需在循环

之前移动以下分配

dayOfWeek[i] = "Sunday";    
dayOfWeek[i] = "Monday";
dayOfWeek[i] = "Tuesday";
dayOfWeek[i] = "Wednesday";
dayOfWeek[i] = "Thursday";
dayOfWeek[i] = "Friday";
dayOfWeek[i] = "Saturday";

Answer 2

当您尝试从阵列中检索数据时......

System.out.println(dayOfWeek[i] + "/'s temperature was: " + temp[i] + " degrees.");

...此时你还没有把任何东西放到数组中。

创建阵列时......

String[] dayOfWeek = new String[NUMBER_OF_DAYS];

这将创建数组并使用 null

填充每个索引

请记住，当您声明并初始化数组时，除非您显式填充数组，否则它将填充数组类型的默认值（在您的情况下为String - 并且String的默认值为null）。

因此，您需要在尝试检索数据之前将实际填充数组的代码行移动到 ...

dayOfWeek[i] = "Sunday"; dayOfWeek[i] = "Monday"; dayOfWeek[i] = "Tuesday"; dayOfWeek[i] = "Wednesday"; dayOfWeek[i] = "Thursday"; dayOfWeek[i] = "Friday"; dayOfWeek[i] = "Saturday"; for (i = 0; i <= temp.length; ++i) { temp[i] = scnr.nextInt(); System.out.println(dayOfWeek[i] + "/'s temperature was: " + temp[i] + " degrees."); }

为什么我的程序打印＆＃34; null＆＃34;而不是字符串？

2 个答案: