java - 尝试读取 int 时出现 InputMismatchException

Question

import java.util.Collections;
import java.util.ArrayList;
import java.util.Scanner;

public class BinarySearch 
{
    public static void main(String [] args)
    {
        Scanner input = new Scanner(System.in);
        ArrayList <Integer> a = new ArrayList <Integer> ();
        System.out.println("Enter elements of your array, input an alphabet in order to exit");
        while(input.hasNextInt()) //takes input from the user until data type becomes something other than int
        {
            int i = input.nextInt();
            a.add(i);
        }
        Collections.sort(a); //Sorts the arrayList
        System.out.print("Enter a value which you wish to search in the array- ");
        int value = input.nextInt();
        System.out.println(contains(a,value));
    }




    public static String contains(ArrayList<Integer> a, int value) //Uses the binary search algorithm to search for an element in the arrayList
    {
        int low=0;
        int high=a.size()-1;
        while (low<=high)
        {
            int mid = (high + low)/2;
            if (value==a.get(mid))
            return value+" is present in the given array at   position "+(mid+1);
            else if(value<a.get(mid))
            high=mid-1;
            else
            low=mid+1;
        }
        return value+"is not present in the given array";
    }



}

在我输入 arrayList 的所有元素后，这段代码给我一个不寻常的错误。 错误是:- 在线程“main”中的 arrayException 中输入一个您希望搜索的值

java.util.InputMismatchException
    at java.util.Scanner.throwFor(Unknown Source)
    at java.util.Scanner.next(Unknown Source)
    at java.util.Scanner.nextInt(Unknown Source)
    at java.util.Scanner.nextInt(Unknown Source)
    at BinarySearch.main(BinarySearch.java:19)

Answer 1

你的程序告诉我们:

Enter elements of your array, input an alphabet in order to exit

然后只要输入了 int 就循环，然后停止但永远不会读取字母字符。

然后你的程序告诉我们

Enter a value which you wish to search in the array

并直接尝试从扫描仪读取一个int

int value = input.nextInt();

但输入的下一个仍然是字母字符，因为您从未阅读过它，因此 InputMismatchException。

关于异常的文档非常清楚它的原因:

Thrown by a Scanner to indicate that the token retrieved does not match the pattern for the expected type, or that the token is out of range for the expected type.

---

现在如何解决这个问题？

当您退出第一个阅读循环以跳过字母字符时，您可以简单地添加对 input.next 的调用:

while (input.hasNextInt()) {
    int i = input.nextInt();
    a.add(i);
}
input.next();
Collections.sort(a);
System.out.print("Enter a value which you wish to search in the array");
int value = input.nextInt();