Polymorphism

Polymorphism essential means that if you have a child class of a parent class you can use the child class anywhere you would use the parent class.  For example you can declare variable with type of parent class to objects of child class. Then when you call a method to that variable it will call the method in the child class. When you run the method the type of the variable doesn’t matter. What matters is the type object containing the variables that’s going to run. So if you make a variable with a parent class type, but it refers to a child class object. It’s going to run the code in the child class.

Below shows many examples of polymorphism. In the main method I made a tree object and a plant object. Tree is a child class of plant. So we can declare a variable type plant to a tree object. We can now call a method that is in both the plant and tree class. When the method is called it will run the code in the tree class. If you try and call a method not in the plant class using a tree object it won’t work. This is shown in the comment below where shedLeaves is a method only in the tree class.

public class App {

     

      public static void main(String[] args) {

            Plant plant1 = new Plant();

            Tree tree = new Tree();         

            Plant plant2 = tree;

         

            plant2.grow();          

            tree.shedLeaves();

        

            //plant2.shedLeaves();

          

            doGrow(tree);

  

      }

    

      public static void doGrow(Plant plant){

            plant.grow();

      }

}