input miss match control in java with try catch

Question

i wrote this code to control input so user cannot enter anything except integers but problem is that: when an Exception occures, the message in Exception block is continousely printed and never ends, what i can do ?

public static void main(String[] args) {
    Scanner scanner = new Scanner(System.in);
    int i=0;
    boolean success = false;
    
    System.out.println("Enter an int numbers :");
    
    while(!success) {//"while loop" will continue until user enters an integer
        try {
            i = scanner.nextInt();
            success=true;//if user entered an integer "while loop" will end, or if user entered another type Exception will occur
            
        }catch(InputMismatchException e) {
            System.out.println(" enter only integers ");
        }
    }
    System.out.println(i);
}

that's a good idea. thanks i must learn how to use hasNextInt for my code — amir, Dec 27 '21 at 12:46

Abdelrahman Nassar · Answer 1 · 2021-12-27T14:02:09.490

1

you should add scanner.nextLine(); in your catch block

the explenation is that you need to clear the scanner and to do so you should use nextLine()

" To clear the Scanner and to use it again without destroying it, we can use the nextLine() method of the Scanner class, which scans the current line and then sets the Scanner to the next line to perform any other operations on the new line."

for more understanding visits the link

your code will look like this

public static void main(String[] args) {
    Scanner scanner = new Scanner(System.in);
    int i=0;
    boolean success = false;
    
    System.out.println("Enter an int numbers :");
    
    while(!success) {//"while loop" will continue until user enters an integer
        try {
            i = scanner.nextInt();
            success=true;//if user entered an integer "while loop" will end, or if user entered another type Exception will occur
            
        }catch(InputMismatchException e) {
            System.out.println(" enter only integers ");
            scanner.nextLine();
        }
    }
    System.out.println(i);
}

edited Dec 27 '21 at 14:02

answered Dec 27 '21 at 08:32

Abdelrahman Nassar

197
3
10

that does not work , sorry because result of nextLine() is String and cannot be saved in i ( i is an integer) – amir Dec 27 '21 at 12:44
@amir it will work, do not replace `scanner.nextInt()` with `scanner.nextLine()` ..... just add `scanner.nextLine()` in the catch block, and leave `scanner.nextInt()` as it is – Abdelrahman Nassar Dec 27 '21 at 12:52
looks like you wanted to comment for the answer above mine – Abdelrahman Nassar Dec 27 '21 at 12:54
and btw, you are right, if you replaced `nextInt()` with `nextLine()` it will not work, .... but that is not what I said – Abdelrahman Nassar Dec 27 '21 at 12:57

ErayZaxy · Accepted Answer · 2021-12-27T12:47:58.147

0

Add scanner.nextLine(); in your try and catch block. Like this

while(!success) {//"while loop" will continue until user enters an integer
        try {
            i = scanner.nextInt();
            success=true;//if user entered an integer "while loop" will end, or if user entered another type Exception will occur
            scanner.nextLine();
            
        }catch(InputMismatchException e) {
            System.out.println(" enter only integers ");
            scanner.nextLine();
        }
    }

You can also add just one scanner.nextLine() in the finaly block, which should be below catch

edited Dec 27 '21 at 12:47

answered Dec 27 '21 at 08:50

ErayZaxy

66
2
8

that does not work , sorry because result of nextLine() is String and cannot be saved in i ( i is an integer) – amir Dec 27 '21 at 12:44
you dont' save it in nothing, just type scanner.nextLine(); after your success=true line – ErayZaxy Dec 27 '21 at 12:45

input miss match control in java with try catch

2 Answers2