我正在构建一个程序，该程序接受未定义数量的输入，将它们存储在数组列表中，并且仅在退出程序之前打印变量

Question

我无法理解它：我要求一个循环，最后询问用户是否要重复该过程。 但是在这样做时，我从根本上重置了循环的计数器，因为我调用了整个方法，如果用户想要插入另一组数据因此我不能将我的数组填充到索引 0 之外，并引入一个管理数量的全局变量重复代码的次数也无济于事。 这是代码：

  public class Main  {
    public static Scanner input = new Scanner(System.in);
    public static int counter = 0; 
    public static void main (String[] args) {
        inputdata();
        
    }
    public static void repeat (ArrayList<String> names, ArrayList<Integer> ages, ArrayList<Double> passinggrades) {
        System.out.println("Want to insert another student? y/n");
        String goon = input.nextLine();
        if (goon.equalsIgnoreCase("n")) {
            System.out.println("thank you for using the program. exiting...");
            showdata(names, ages, passinggrades);
            System.exit(0);
        }
        else if (goon.equalsIgnoreCase("y")) {
            
            inputdata();
        }
        else {
            System.out.println("Wrong input: " + goon + " is not y or n");
            repeat(names, ages, passinggrades);
        }
    }
    public static void inputdata () {
        ArrayList<String> names = new ArrayList<String>();
        ArrayList<Integer> ages = new ArrayList<Integer>();
        ArrayList<Double> passinggrades = new ArrayList<Double>();
        
        for (int i = counter; i != -1; i++) {
            System.out.print("insert name here: ");
            String name = input.nextLine();
            System.out.print("insert age here: ");
            int age = input.nextInt();
            System.out.print("insert passing grade here: ");
            double passinggrade = input.nextDouble();
            Student student = new Student(name, age, passinggrade);
            names.add(i, student.name);
            ages.add(i, student.age);
            passinggrades.add(i, student.passinggrade);
            input.nextLine();
            System.out.println(counter);
            counter ++;
            repeat(names, ages, passinggrades);
        }
    }
    public static void showdata (ArrayList<String> names, ArrayList<Integer> ages, ArrayList<Double> passinggrades) {
        System.out.print("Name |");
        System.out.print("Age |");
        System.out.print("Grade |");
        System.out.println();
        for (int i = 0; i < names.size(); i++) {
            System.out.print(names.get(i)+ " |");
            System.out.print(ages.get(i)+ " |");
            System.out.print(passinggrades.get(i)+ " |");
            System.out.println();
        }
    }
}

学生班：

public class Student {
    String name;
    int age;
    double passinggrade;
    
    
    Student(String name, int age, double passinggrade){
        this.name = name;
        this.age = age;
        this.passinggrade = passinggrade;
    }
}

当我尝试插入第一个元素之外的元素时，编译器给出的错误：

Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 1, Size: 0
    at java.base/java.util.ArrayList.rangeCheckForAdd(ArrayList.java:756)
    at java.base/java.util.ArrayList.add(ArrayList.java:481)
    at simpleconstructor2.Main.inputdata(Main.java:42)
    at simpleconstructor2.Main.repeat(Main.java:22)
    at simpleconstructor2.Main.inputdata(Main.java:48)
    at simpleconstructor2.Main.main(Main.java:9)

Answer 1

我为 inputdata() 起草了一个快速版本的代码，它消除了对 repeat() 的需求。

    ArrayList<Student> students = new ArrayList<>();  //declare and initialize your arrayList outside the loop so it is not redeclared and replaced in each iteration.
    while (true){
        System.out.print("insert name here: ");
        String name = input.nextLine();
        System.out.print("insert age here: ");
        int age = input.nextInt();
        System.out.print("insert passing grade here: ");
        double passinggrade = input.nextDouble();
        Student student = new Student(name, age, passinggrade);
        //redundant-------------------------------------
        //names.add(i, student.name);
        //ages.add(i, student.age);
        //passinggrades.add(i, student.passinggrade);
        //----------------------------------------------
        students.add(student);
        input.nextLine();

        //you can probably fit this in a boolean method that will break or return depending on value of goon
        System.out.println("Want to insert another student? y/n");
        String goon = input.nextLine();
        if (goon.equalsIgnoreCase("n")) {
            System.out.println("thank you for using the program. exiting...");
            showdata(students);  //modify your showdata() method accordingly for an ArrayList of Student
            break;
        }else if (goon.equalsIgnoreCase("y")) {
            continue;
        }else {
            System.out.println("Wrong input: " + goon + " is not y or n");
            continue;
        }
    }