java为什么我的程序打印“null”而不是字符串？

Question

我正在尝试创建一个程序来打印一周中每天的温度。我不知道为什么我的代码打印“null”而不是一周中的每一天。我以前从未见过这个错误（我正在学习编程课程），在教科书中找不到任何信息。这是我到目前为止的代码

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();
}

很明显，数组放错了位置，但它现在不会影响输出，所以我想表明我至少在这里尝试过。实际上，我唯一的问题是如何打印一周中的哪一天。也许还有一点关于如何处理上面的两个阵列的指导

Answer 1

当您尝试从数组中检索数据时

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

。。。此时您实际上还没有向数组中放入任何内容

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，在声明和初始化数组时，除非显式填充数组，否则数组将填充数组类型的默认值（在您的示例中为字符串，字符串的默认值为null）

因此，您需要将实际填充数组的代码行移动到之前尝试检索数据的点

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.");
}

Answer 2

只需在for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";