Java Runtime Polymorphism

• We will create two classes "Tree and Size". 
• Size class extends Tree class and overrides its reshape() method. 
• We call the reshape method by the reference variable of Parent class. 
• Since it refers to the subclass object and subclass method overrides the Parent class method, subclass method is called at runtime.

Super And Sub Classes

class Tree {

public void reshape() {

System.out.println("Super tree size is big..");

}

}

class Size extends Tree {

public void reshape() {

System.out.println("Sub tree size is small..");

}

public void shape() {

super.reshape();

}

}

Main Method

public static void main(String[] args) {

        // upcasting

Tree tree = new Size();

tree.reshape();

}