Java例外：为什么我的程序没有终止？

Question

When I run my simple code and enter char instead of integer value which was supposed to be Entered. Program, listed below is supposed to be terminated after printing "error please Enter integer value" .

But this code, also printing the line after Occurrence of error

import java.util.InputMismatchException;
import java.util.Scanner;

public class Test { 
    public static void main(String[] args) {
        System.out.println("enter value integer ");
        Scanner sn = new Scanner(System.in);
        try{
            int a = sn.nextInt();
        } catch (InputMismatchException ex){
            System.out.println("error please enter integer value");
        }
        System.out.println("not terminating");
    }
}

Answer 1

It is terminating, it just prints out the System.out first. This is as expected - it jumps into the catch block, and then continues.

Answer 2

But this code, also printing the line after Occurrence of error

Because it is out side of try-catch, that is the advantage of exception handling.

Exception handling prevents the abnormal termination of program due to run time error. And that is what happened.

See also

• exception handing docs

Answer 3

    System.out.println("enter value integer ");
    Scanner sn = new Scanner(System.in);
    try {
        int a = sn.nextInt();
    } catch (InputMismatchException ex) {
        System.out.println("error please enter integer value");
        // you are catching input mis match here 
        // exception will catch and program continues
    }
    System.out.println("not terminating"); // this is out side the try-catch

So you will get this line in your out put too.

Answer 4

After entering the catch block, flow continues on, so the next line to execute is the bottom print.

If you want to terminate from within the catch :

try {
    int a = sn.nextInt();
} catch (InputMismatchException ex) {
    System.out.println("error please enter integer value");
    return; // program will end
}

Answer 5

If you want it to be terminated you need to re-throw the exception eg:

System.out.println("enter value integer ");
Scanner sn = new Scanner(System.in);
try {
    int a = sn.nextInt();
} catch (InputMismatchException ex) {
    System.out.println("error please enter integer value");

    throw new RuntimeException(ex);
}

System.out.println("not terminating"); // this is out side the try-catch

That way the last system output would not be printed and you would get a stacktrace instead.