获取错误消息“线程“main”java.util.InputMismatchException 中的异常”

Question

public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int iteam = sc.nextInt();
    Student[] students = new Student[iteam];
    int id;
    String name;
    String city, s_city;
    double marks, s_marks;

    for (int i = 0; i < iteam; i++) {
        id = sc.nextInt();
        name = sc.nextLine();
        city = sc.nextLine();
        marks = sc.nextDouble();
        students[i] = new Student(id, name, city, marks);

    }
}

I got an error " Exception in thread "main" java.util.InputMismatchException

    at java.util.Scanner.throwFor(Unknown Source)
    at java.util.Scanner.next(Unknown Source)
    at java.util.Scanner.nextDouble(Unknown Source)"

I also, try using next() but the same error exists. and I also import java.util.Scanner.

Answer 1

There's not a lot of info here, but I see a problem that could definitely be causing your problem.

When you read a numeric value from a line, and expect the user to have hit return to submit that value, you have to consume the end of line before you can move on. The Scanner doesn't do this automatically. To have the user enter 4 values, hitting return after each entry, your input loop should look like this:

for (int i = 0; i < iteam; i++) {

    id = sc.nextInt(); sc.nextLine();

    name = sc.nextLine();

    city = sc.nextLine();

    marks = sc.nextDouble(); sc.nextLine();

    students[i] = new Student(id, name, city, marks);

}

Answer 2

The previous solution was not complytly right. After a little debug-session i figured the following solution out:

public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int iteam;
    iteam = sc.nextInt();
    Student[] students = new Student[iteam];
    int id;
    String name;
    String city;
    double marks;

    for (int i = 0; i < iteam; i++) {
        id = sc.nextInt();
        name = sc.next();
        city = sc.next();
        marks = sc.nextDouble();
        students[i] = new Student(id, name, city, marks);
    }
}

A little explanation for you: The methods next() , nextInt() and nextDouble() scans the next token as a input value. But most important the Return doesn't count, because your bash interpreted this as your input.

Also, your keyboard input is localized interpreted, especially if you want to read a double. For example, the English separator is written as DOT and in German as a COMMA .

Answer 3

You need to call sc.nextLine() after reading the first int from the input as you are reading 4 values. Scanner#nextInt() only reads the integer, but does not read the newline "\\n" ; you will need to consume the newline using Scanner#nextLine .

public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int iteam = sc.nextInt();
    Student[] students = new Student[iteam];
    int id;
    String name;
    String city, s_city;
    double marks, s_marks;
    for (int i = 0; i < iteam; i++) {
        id = sc.nextInt();
        sc.nextLine();//call next line to prevent exception
        name = sc.nextLine();
        city = sc.nextLine();
        marks = sc.nextDouble();
        students[i] = new Student(id, name, city, marks);
    }
}

Full Working Example:

import java.util.Scanner;
public class MyClass {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int iteam = sc.nextInt();
        Student[] students = new Student[iteam];
        int id;
        String name;
        String city, s_city;
        double marks, s_marks;
        for (int i = 0; i < iteam; i++) {
            id = sc.nextInt();
            sc.nextLine();
            name = sc.nextLine();
            city = sc.nextLine();
            marks = sc.nextDouble();
            students[i] = new Student(id, name, city, marks);
        }
        for(Student s: students){
            System.out.println(s);
        }
    }
    private static class Student{
        private int id;
        private String name;
        private String city;
        private double marks;
        public Student(int id, String name, String city, double marks){
            this.id = id;
            this.name = name;
            this.city = city;
            this.marks = marks;
        }
        public String toString(){
            return "[Student] Id: "+this.id+", Name: "+this.name+", City: "+this.city+", Mark: "+this.marks;
        }
    }
}