扫描多个输入时没有此类元素异常

Question

我是java编程新手，我试图学习java编程中类和对象的用法，同时编写下面的代码，我得到了一个例外。

java.util.NoSuchElementException

用于样本输入

5

1 2 3 4 5

这里，第一行包含元素数(在本例中为5)，下一行包含元素。

当在类选举中接受for循环中的输入时，我得到了异常。

我试着搜索堆栈溢出和其他资源，但仍然找不出如何删除这个异常。

import java.io.*;
import java.util.Scanner;
public class TestClass {
     public static void main(String[] args) {
        int n;
        Scanner input = new Scanner(System.in);
        n = input.nextInt();
        input.nextLine();
        Election obj = new Election(n);
        obj.getVotes();
    }
}
class Election {
     int n,v1,v2,v3,v4,v5,d;
     public Election(int n) {
          this.n = n;
          v1=v2=v3=v4=v5=d=0;
     }
     public void getVotes() {
       Scanner sc = new Scanner(System.in);
       for(int i = 0 ; i < 1 ; i++) {
         int var = sc.nextInt();
         switch(var) {
             case 1: ++v1; break;
             case 2: ++v2; break;
             case 3: ++v3; break;
             case 4: ++v4; break;
             case 5: ++v5; break;
           default: ++d; break;
         }
       }     
     }
}

Answer 1

看上去我有点晚了，但既然你接受的回答更多的是评论而不是解决方案，我还是会发这篇文章。

下面是您提供的代码的简单偏差，但是达到了预期的结果！

我会带你经历这一切：

public class MyTest {
    public static void main(String[] args) {

        //First of all, we need an instance of an Election-type object, so
        //that we can call its methods and get votes from users.
        Election e = new Election();
        //Now we can easily call the method getVotes(), as defined in Election class.
        //What happens here, is that the program will 'jump' to the getVotes() method
        //and it will execute every line of code in that method. Then it will
        //'return' to where it 'left off' in the main() method. Since getVotes()
        //is of type 'void', it will not return anything. It will just 'jump' back.
        e.getVotes();

        //Now, you can use testResult() method, to see the values of the variables.
        e.testResult();
    }
}

现在，让我们看一下类Election以及它是如何工作的。

public class Election {
    private final int VOTES_NUM = 1;
    private int v1,v2,v3,v4,v5,d;

    public Election() {
        v1=v2=v3=v4=v5=d=0;
        //print now, just to show that all variables = 0
        testResult();
    }

    //Simple method that prints value of each variable. We use this for testing
    public void testResult(){
        System.out.println("v1 = "+v1);
        System.out.println("v2 = "+v2);
        System.out.println("v3 = "+v3);
        System.out.println("v4 = "+v4);
        System.out.println("v5 = "+v5);
        System.out.println("d = "+d);
    }

    private int getInput(){
       //First of all, we need a Scanner to take user input. 
       //You do that in your own code too. We simply move it in this method instead.
        Scanner input = new Scanner(System.in);

        //You also need variable to hold the user input. 
        //(Always give meaningful names to all entities)
        int userInput;

        System.out.print("Please enter vote number here: ");

        //the next part has to be in a try-catch block, 
        //to avoid exceptions like InputMismatchException, etc..
        try{
            //Get user input
            userInput = input.nextInt();
        }
        //If user enters letter, or symbol, or something else that isn't an integer,
        //then inform them of the mistake they made and recursively call this method,
        //until they get it right!
        catch (InputMismatchException ime){
            System.out.println("Please enter only a single number");
            return getInput();
        }

        //If all goes well, return the user input
        return userInput;
    }

    public void getVotes() {
        //'VOTES_NUM' is a constant that defines the times the 
        //loop will iterate (like Macros in 'C')
        for(int x=0; x<VOTES_NUM; x++)
            int n = getInput();
        //then let the switch statement increment one of the variables
        switch(userInput) {
            case 1: ++v1; break;
            case 2: ++v2; break;
            case 3: ++v3; break;
            case 4: ++v4; break;
            case 5: ++v5; break;
            default: ++d; break;
        }
    }
}

Answer 2

我想你发布的密码不见了。您发布的代码工作正常，只有在我在input.close()之前编写obj.getVotes()时，我才实现了异常。当您想关闭扫描器时，您应该在代码完成后进行此操作。因此，如果在obj.getVotes()之后关闭输入，则不应该出现任何错误。

Answer 3

我试着在一个简短的主类中运行您的代码，没有任何异常。我就是这样运行您的方法的：

public static  void main(String...args){
    Election election = new Election(10);
    election.getVotes();
    System.out.println(election.v1);
    System.out.println(election.v2);
    System.out.println(election.v3);
    System.out.println(election.v4);
    System.out.println(election.v5);
    System.out.println(election.d);
}

我的输入是1 2 3 4 5 6 7 1 2，控制台输出是：

2 // v1
3 // v2
1 // v3
1 // v4
1 // v5
2 // d

我对你的节目做了个小小的改动。在getVotes()方法中的for循环中，我将条件更改为i<n (而不是发布的代码中的i<1 )。