Question

当我尝试运行此代码时noOfSub()方法正确执行; 但GC()方法面临以下问题：

Enter the number of subjects:
2
Enter Your Subject 1 Grade:
s
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 1
    at GPA.GC(GPA.java:21)
    at GPA.main(GPA.java:35)
Java Result: 1

这是我的代码：

 import java.util.Scanner;  

 public class GPA {   

   public int noOfSubjects;  
   public int i=1;
   Scanner gradeInput = new Scanner(System.in);
   String[] grade = new String[noOfSubjects];
   int[] credit = new int[noOfSubjects];

    public void noOfSub() {
        System.out.println("Enter the number of subjects:");
        Scanner sub = new Scanner(System.in);
        noOfSubjects = sub.nextInt();   
    } 
    public void GC() {
        while(i<=noOfSubjects)
        {
          System.out.println("Enter Your Subject "+i+" Grade:" );

            grade[i] = gradeInput.nextLine();

            System.out.println("Enter the Subject "+i+" Credit:");

            credit[i] = gradeInput.nextInt();
                i++;              
        }
    }
    public static void main(String[] args) {
       GPA obj = new GPA();
       obj.noOfSub();
       obj.GC();
    }  
}

Answer 1

当你这样做时：

public int noOfSubjects;

noOfSubjects设置为0，即default value

所以当你有以下代码时：

 String[] grade = new String[noOfSubjects];

它基本上意味着，

String[] grade = new String[0]; //create a new String array with size 0

为你创建一个空数组。

所以当你这样做时，

grade[i] = gradeInput.nextLine(); //where i is 1

你得到：

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 1
    at GPA.GC(GPA.java:21)
    at GPA.main(GPA.java:35

因为1中没有索引String[] grade。

Answer 2

如果要从用户获取数组的大小，请在从stdin获取数组后创建该数组。否则，它将创建一个大小为0的数组，这是java中int的默认值。

Answer 3

分离您的声明和初始化

String[] grade = null;
int[] credit = null;
...
noOfSubjects = scan.nextInt();
grade = new String[noOfSubjects];
credit = new int[noOfSubjects];

Answer 4

数组初始化时出现问题。您可以在从用户那里获取输入后初始化数组。

例如：

public void noOfSub() {
  System.out.println("Enter the number of subjects:");
  Scanner sub = new Scanner(System.in);
  noOfSubjects = sub.nextInt();   
  grade = new String[noOfSubjects];
  credit = new int[noOfSubjects];
}

改变你的状态。而不是你使用

  while(i < noOfSubjects)

并设置i = 0

Answer 5

为什么不使用ArrayList，因为不知道数组的大小

public class GPA {   

 public int noOfSubjects;  
 public int i=0;
 Scanner gradeInput = new Scanner(System.in);
 List<String> grade = new ArrayList<>();
 List<Integer> credit = new ArrayList<>();

    public void noOfSub(){
        System.out.println("Enter the number of subjects:");
        Scanner sub = new Scanner(System.in);
        noOfSubjects = sub.nextInt();   
    } 
    public void GC(){
        while(i<noOfSubjects)
        {
          System.out.println("Enter Your Subject "+(i+1)+" Grade:" );

            grade.add(gradeInput.nextLine());

            System.out.println("Enter the Subject "+(i+1)+" Credit:");

            credit.add(gradeInput.nextInt());
            gradeInput.nextLine(); 
                i++;              
        }
    }
            public static void main(String[] args) {
               GPA obj = new GPA();
               obj.noOfSub();
               obj.GC();
            }  
    }

注意：我在gradeInput.nextLine()之后添加了i++，因为Scanner.nextInt()方法不会消耗您输入的最后一个换行符，因此会消耗换行符在下一次调用Scanner.nextLine()时，我会在gradeInput.nextLine()之后触发一个空白的gradeInput.nextInt()来调用该行的剩余部分，包括换行符

Answer 6

由于noOfSubjects具有运行时值，因此代码应为：

import java.util.Scanner;

公共类GPA {

public int noOfSubjects;
public int i = 0;
Scanner gradeInput = new Scanner(System.in);
String[] grade;
int[] credit;

public void noOfSub() {
    System.out.println("Enter the number of subjects:");
    Scanner sub = new Scanner(System.in);
    noOfSubjects = sub.nextInt();
    grade = new String[noOfSubjects];
    credit = new int[noOfSubjects];
}

public void GC() {

    while (i < noOfSubjects) {
        System.out.println("Enter Your Subject " + (i + 1) + " Grade:");

        grade[i] = gradeInput.next();

        System.out.println("Enter the Subject " + (i + 1) + " Credit:");

        credit[i] = gradeInput.nextInt();
        i++;
    }

    for (int j = 0; j < grade.length; j++) {
        System.out.println(grade[j] + " " + credit[j]);
    }

}

public static void main(String[] args) {
    GPA obj = new GPA();
    obj.noOfSub();
    obj.GC();
}

}

如何从循环语句中的用户获取字符串或整数数组？

6 个答案: