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，这段代码给我一个异常错误。错误是：- 在 thread "main"

的 arrayException 中输入要搜索的值

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 int 就循环，然后停止但永远不会读取字母字符。

那你的程序告诉我们

Enter a value which you wish to search in the array

并直接尝试从扫描器

读取一个int

int value = input.nextInt();

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

关于异常的文档非常清楚原因：

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？

您可以在退出第一个阅读循环时简单地添加对 input.next 的调用以跳过字母字符：

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();

尝试读取 int 时出现 InputMismatchException

InputMismatchException when trying to read an int

java

java.util.scanner