User input

[maydoncillo]

hi,
How will i check if the user input is valid digit/numbers..?
How will i do it in java..?

[heat84]

One soultion may be to use the Character class and then checking if the characters in a string are digits or not .

Read the java docs , I am sure you will get the information you need.

[JosAH]

hi,
How will i check if the user input is valid digit/numbers..?
How will i do it in java..?

Note that e.g. de Integer and Double class can convert a String to the type they
wrap. If the String doesn't represent a valid wrapped type (int or double in this
example) an NumberFormatException is thrown.

kind regards,

Jos

[BigDaddyLH]

Demo: This reads from System.in, a line at a time and attempts to parse the line as an int.

import java.io.*;
 
public class NumberInputExample {
    public static void main(String[] args) throws IOException {
        BufferedReader in = new BufferedReader(
            new InputStreamReader(System.in));
        String line;
        while((line = in.readLine()) != null) {
            try {
                int n = Integer.parseInt(line);
                System.out.format("(%1$d)*(%1$d)=%2$d%n", n, n*n);
            } catch (NumberFormatException e) {
                System.out.format("'%s' cannot be parsed%n", line);
            }
        }
    }
}