Check if the string contains only numbers

Question

How can I check if a string contains only numbers?

For example, you can’t have * / = e etc... only numbers.

Because I need to convert a string to int and if you type letters, symbols will generate an error.

Answer 1

One of the ways to know if the string contains only numbers, is using a regular expression

"1239417".matches("[0-9]+");   // true
"12312a".matches("[0-9]+");    // false
"12312+".matches("[0-9]+");    // false

In regular expression [0-9]+

• [ and ]: delimits a set of characters
• 0-9: the character set, anyone between 0 and 9
• +: of the defined expression, must correspond to 1 or more groups

Answer 2

Another way is to try the conversion to integer:

    String input = "123s";
    try {
        Integer.valueOf(input);
    } catch (Exception e) {
        System.out.println("Número inválido");
    }