thermometer c = new centigrade();
thermometer f = new fahrenheit();
displayer cd = new displayer("centigrade");
displayer fd = new displayer("fahrenheit");
prompter cp = new prompter("enter centigrade value");
prompter fp = new prompter("enter fahrenheit value");
show sc = new show(c,cd);
show sf = new show(f,fd);
update uc = new update(c,cp);
update uf = new update(f,fp);