为什么数组值在切换情况下不保留？

Question

为什么数组值没有保存在我的开关函数中？ 首先，我按1，创建我的名册值。 创建值后，按2会导致ArrayOutOfBound错误。 谁能告诉我我在做什么错？

请忽略FileNotFoundExceptions。 解决我做错的事情后，需要在该部分上进行工作。

public static Scanner keyboard = new Scanner(System.in);
public static int numStudents;
public static String[] nameOfStudent;
public static int[] broncoID;
public static int[] grade;

^这些是我声明的变量

public static void main(String[] args) throws FileNotFoundException {

    startMenus(keyboard);
}

public static void startMenus(Scanner sc) throws FileNotFoundException {
    while (true) {
        System.out.println("(Enter option # and press ENTER)\n");
        System.out.println("1. Create new Roster");
        System.out.println("2. Display Current Roster");

        int option = sc.nextInt();

        sc.nextLine();

        switch (option) {
        case 1:
            createRoster();
            break;
        case 2:
            displayRoster();
            break;
        default:
            System.out.println("Unrecognized Option!\n");
        }
    }
}

public static void createRoster() throws FileNotFoundException {

    System.out.println("Please list how many students there are.");

    numStudents = keyboard.nextInt();

    nameOfStudent = new String[numStudents];
    broncoID = new int[numStudents];
    grade = new int[numStudents];

    keyboard.nextLine();

    for(int i = 0; i < numStudents; i++){
        System.out.println("Please enter full name of Student.");
        nameOfStudent[i] = keyboard.nextLine();
        System.out.println("Now please enter the BroncoID of Student.");
        broncoID[i] = keyboard.nextInt();
        System.out.println("Now please enter grade of Student (0-100)");
        grade[i] = keyboard.nextInt();
        keyboard.nextLine();
    }
    System.out.println("Roster successfully created!");
    for (int i = 0; i < numStudents ; i++){
        System.out.printf("Name: %9s\t Bronco ID: %5d \t Grade: %2d \n", nameOfStudent[i], broncoID[i], grade[i]);
    }
}

public static void displayRoster(){
    System.out.printf("Name: %9s\t Bronco ID: %5d \t Grade: %2d \n", nameOfStudent[1], broncoID[1], grade[1]);

}

第一种情况下的printf有效，但第二种情况下无效。 错误我得到：

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 1
at Roster.displayRoster(Roster.java:115)
at Roster.startMenus(Roster.java:36)
at Roster.main(Roster.java:16)

Answer 1

数组始终以索引0开头。您向数组添加了一个“ Roster”。 该名册将获得索引0。在displayRoster()方法中，您希望显示索引1，但是您的数组仅具有索引0。因此它将获得ArrayIndexOutOfBoundsException。

代替：

System.out.printf("Name: %9s\t Bronco ID: %5d \t Grade: %2d \n", nameOfStudent[1], broncoID[1], grade[1]);

尝试：

System.out.printf("Name: %9s\t Bronco ID: %5d \t Grade: %2d \n", nameOfStudent[0], broncoID[0], grade[0]);

Answer 2

您在switch语句中使用2种情况：

情况1和2

但是，您将输入作为createroster输入1，将displayroster输入为4

在switch语句中使用“案例1”和“案例4”。 或使用：

System.out.println("1. Create new Roster");
System.out.println("2. Display Current Roster");

Answer 3

1. 最好将displayRoster方法修改为：

    public static void displayRoster() { System.out.println("Enter the record number to be displayed[1 to numStudents :"); int i = keyboard.nextInt(); if(i <= nameOfStudent.length) System.out.printf("Name: %9s\\t Bronco ID: %5d \\t Grade: %2d \\n", nameOfStudent[i-1], broncoID[i-1], grade[i-1]); else System.out.println("This is where you are trying to access element out of bound."); } 

2. 输入option = 4指向代码中的default开关大小写，应为S.out“ Unrecognized Option!"