stop program running when user input is correct, if incorect give chance over and over

Question

im beginner in java programing, have task need to be completed and looking for some useful tips. writing program which requires from user correct Float input, if input is incorrect, program gives another chance until correct input, my problem is next, when i enter incorrect input it runs non stop,, any ideas?

   public static void main(String[] args) {
    Scanner in = new Scanner(System.in);
    float f = 0;
    int x = 1;
    do {
        try {
            System.out.print("Enter an float:");
            f = in.nextFloat();
            x =2;

        } catch (InputMismatchException e) {
            System.err.println("Incorrect entry.");

        }
        System.out.println("Your entry is:" + f);

    }
    while(x==1);
}

Add `in.nextLine();` at the end of your `while` loop, to swallow the rest of the line. — Arnaud, Mar 16 '16 at 16:33
What we can consider a correct input in this case well i have executed the program for input 3,7,45.45 it only runs once.Any example of incorrect input ?? — Abhishekkumar, Mar 16 '16 at 16:36
incorect input can be anything, letters for example, input jbvirebv and you will see, correct input, is floating number, — George Weekson, Mar 16 '16 at 16:46

score 1 · Accepted Answer · answered Mar 16 '16 at 16:51

1

Do this and you will get the output you want from your program

public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        float f = 0;
        int x = 1;
        do {
            try {
                System.out.print("Enter an float:");
                f = in.nextFloat();
                x = 2;

            } catch (InputMismatchException e) {
                System.err.println("Incorrect entry.");
                in.next();

            }

        } while (x == 1);
        System.out.println("Your entry is:" + f);

    }

You just need to add in.next() in catch block to continue the process.

answered Mar 16 '16 at 16:51

Abhishekkumar

1,044
7
21

thanks a lot @abhishekkumar, now it works – George Weekson Mar 16 '16 at 16:53
please choose this as accepted answer if your problem is resolved – Abhishekkumar Mar 16 '16 at 16:54
i did mate. thanks again – George Weekson Mar 16 '16 at 16:55

score 1 · Answer 2 · answered Mar 16 '16 at 16:59

As an alternative to the accepted answer, you may want to :

1) Check that the next token is a float hasNextFloat()

2) If it isn't, swallow the whole line nextLine()

 Scanner in = new Scanner(System.in);
        float f = 0;
        String entry;
        int x = 1;
        do {

            System.out.print("Enter an float:");

            if (in.hasNextFloat()) {

                f = in.nextFloat();
                entry = Float.toString(f);
                x = 2;

            } else {

                entry = in.nextLine();
                System.err.println("Incorrect entry.");

            }
            System.out.println("Your entry is: " + entry);

        } while (x == 1);

This has the advantage of getting rid, of wrong input line having multiple tokens (e.g : "aa bb cc").

stop program running when user input is correct, if incorect give chance over and over

2 Answers2