Valid Number

Validate if a given string is numeric.

Some examples:
"0" => true
" 0.1 " => true
"abc" => false
"1 a" => false
"2e10" => true

Note: It is intended for the problem statement to be ambiguous. You should gather all requirements up front before implementing one.

Solution:
This question can be solved easily using regular expression. 

public class Solution {
    
    public boolean isNumber(String s) {
        if(s.trim().isEmpty())  // trim: remove spaces at the heading and trailing
            return false;
        String regex = "[+-]?((\\d+\\.?\\d*)|(\\.\\d+))(e[+-]?\\d+)?";
        if(s.trim().matches(regex))
            return true;
        else
            return false;
    }
}