What will be the output of the following Java code?

import java.util.*;
class properties 
{
    public static void main(String args[]) 
    {
        Properties obj = new Properties();
        obj.put("AB", new Integer(3));
        obj.put("BC", new Integer(2));
        obj.put("CD", new Integer(8));
        System.out.print(obj.keySet());
    }
}