How to limit users to only enter integer into a String variable.

[Loh Jane]

Hi Java Professionals,
I need to allow users only enter integer into a String variable, "input" and I am not sure what statement to use. Please help, thanks a lot in advance.

import java.util.Scanner;
public class assq2b
{
public static void main(String []args)
{
Scanner reader = new Scanner(System.in);
String input,b;
long checked;
System.out.print("Please enter the 12 digit:");
input = reader.nextLine();
if((input.length() < 12) || (input.length() > 12))
{
System.out.println("The entered digits is not equal to 12.");
System.exit(0);
}
else
{
System.out.println("Calculating...");
}

checked =Long.parseLong(input);

[Norm]

You can't control what a user enters, but you can make the program not accept what the user enters.
To do that use a loop that asks the user for input, tests what is input and exit the loop if the input is acceptable. If the input is not acceptable, the loop goes back and asks the user for input again.

One way to test the user's input to be a number is to use the Integer class's parse method inside of a try catch block.

Please edit your post and wrap your code with code tags:
[code=java]
YOUR CODE HERE
[/code]
to get highlighting and preserve formatting.

[Loh Jane]

Hi,
I amended my code but I also need to make the program only accept a 12 digit number and currently it doesn't accept "098765432199".It means the first digit cannot be zero,please help.

Scanner reader = new Scanner(System.in);
String input=" ",b;
long checked;

do {
System.out.print("Please enter a 12 digit number:");
while (!reader.hasNextLong())
{
System.out.println("That's not a number!");
System.out.print("Please renter 12 digit number:");
reader.next();

}
checked =reader.nextLong();
input = Long.toString(checked);
}while (input.length() != 12);
System.out.println("Thanks");

[derekxec]

you need to get the users input before you start the validation so you have something to check it against

you are using a do while loop wrong

do { <--start loop
stuff you want to do at least one time <-- ask for input and receive the input
}while(test here); <---test if the input is good and if its not go back to do and start all over

really you could just use a while loop after you get the users input and if the while loop tests incorrect to ask for input again..then if the users input is correct it wouldn't even execute the body of the while loop

[Norm]

Please edit your post and wrap your code with code tags:
[code=java]
YOUR CODE HERE
[/code]
to get highlighting and preserve formatting.

Its hard to see the logic without the code properly formatted.