Benefit of Polymorphism [closed]

Question

When I started to look for the benefits of polymorphism, I found with this question here. But here I was unable to find my answer. Let me tell what I want to find. Here I have some classes:

class CoolingMachines{     public void startMachine(){         //No implementationion     }     public void stopMachine(){         //No implementationion     } }  class Refrigerator extends CoolingMachines{     public void startMachine(){         System.out.println("Refrigerator Starts");     }     public void stopMachine(){         System.out.println("Refrigerator Stop");     }     public void trip(){         System.out.println("Refrigerator Trip");     } }  class AirConditioner extends CoolingMachines{     public void startMachine(){         System.out.println("AC Starts");     }     public void stopMachine(){         System.out.println("AC Stop");     } }  public class PolymorphismDemo {     CoolingMachines cm = new Refrigerator();     Refrigerator rf = new Refrigerator(); } 

Now here I created two objects in the Demo class and are references of Refrigerator. I have completely understood that from the rf object I am able to call the trip() method of Refrigerator, but that method will be hidden for the cm object. Now my question is why should I use polymorphism or why should I use

CoolingMachines cm = new Refrigerator(); 

when I am OK with

Refrigerator rf = new Refrigerator(); 

Is polymorphic object's efficiency is good or light in weight? What is the basic purpose and difference between both of these objects? Is there any difference between cm.start(); and rf.start()?

Answer 1

It is useful when you handle lists... A short example:

List<CoolingMachines> coolingMachines = ... // a list of CoolingMachines  for (CoolingMachine current : coolingMachines) {     current.start(); } 

Or when you want to allow a method to work with any subclass of CoolingMachines