java - Polymorphism on simple example -

i think i'm starting understand topic, not completely. can explain me on example:

public class solution {     public static void main(string[] args)     {         cow cow = new whale();          system.out.println(cow.getname());     }      public static class cow     {         public string getname()         {             return "im cow";         }     }      public static class whale extends cow     {         public string getname() {             return "im whale";         }     } } 

what difference when called this:

cow cow = new whale(); system.out.println(cow.getname()); 

and this:

whale whale = new whale(); 

system.out.println(whale.getname());

i have same output, in cases or maybe when should call methods cow class, , when form whale class. sorry if gave stupid or simple example. hope undeerstood wanted say. in advance.

it's question understand polymorphism. not sure whale should extends cow ;), can show bit of different structure:

public class solution {     public static void main(string[] args) {         animal animal1 = new cow();         animal animal2 = new whale();          arraylist<animal> myanimals = new arraylist<animal>();         myanimals.add(animal1);         myanimals.add(animal2);         //show animals         (animal animal : arraylist) {             system.out.println(animal.getname());          }       }       public static class animal {         public string getname() {             return "im general animal";         }     }      public static class cow extends animal {         public string getname() {             return "im cow";         }     }      public static class whale extends animal {         public string getname() {             return "im whale";         }     } } 

in above example created animal class extended cow , whale. can create list of animals , display names. in example no difference make object cow cow = new whale(); , whale whale = new whale(); clear you?