In JAVA, also why is my answer wrong, thanks!

NOTE: in mathematics, the square root of a negative number is not real; in Java therefore, passing such a value to the square root function returns a value known as NaN (not-a-number). Given a double variable named areaOfSquare write the necessary code to read in a value, the area of some square, into areaOfSquare and print out the length of the side of that square. HOWEVER: if any value read in is not valid input, just print the message "INVALID". ASSUME the availability of a variable, stdin, that references a Scanner object associated with standard input.

import java.util.Scanner;

class square_root { public static void main (String[] args) { Scanner s=new Scanner(System.in); System.out.print("Enter the area: "); double areaOfSquare=s.nextDouble(); if(areaOfSquare<0) { System.out.println("INVALID"); System.exit(2); } System.out.println("The side of the square is: " +Math.sqrt(areaOfSquare)); } }