Assignemnt #74 and Safe Square Root

Code
/// Name: Yordan Rashkov
/// Period: 7
/// Program Name: safe square root
/// File Name: safesquareroot.java
/// Date Finished: 1/26/2016

import java.util.Scanner;

public class safesquareroot
{
    public static void main( String[] args )
    {
        Scanner keyboard = new Scanner(System.in);
        
        boolean isPositiveNumber = true;
        double g1, squareRoot;
        int number;
        
        squareRoot = number / 2;
        
        System.out.println(" SQUARE ROOT! ");
        System.out.println();
        System.out.println("Enter a number: ");
        number = keyboard.nextInt();
        System.out.println();
        
        if ( number == 0 )
        {
            System.out.println("Square root of "+number+" = "+0);
        }
        else if ( number<0 )
        {
        System.out.println(" You cannot take the square root of a negative number! ");
        System.out.println();
        System.out.println();
        System.out.println(" Choose another number please: ");
        number = keyboard.nextInt();
        }
        
        System.out.println();
        System.out.println();
        System.out.println();
        
        while((g1-squareRoot)!=0);
        {
            g1=squareRoot;
            squareRoot = (g1 + (number/g1))/2;
        }
        if(isPositiveNumber)
        {
            System.out.println("Square roots of "+number+" are ");
            System.out.println("+"+squareRoot);
            System.out.println("-"+squareRoot);
        }
        else
        {
            System.out.println("Square roots of -"+number+" are ");
            System.out.println("+"+squareRoot+" i");
            System.out.println("-"+squareRoot+" i");
        }
    }
}