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Methods Overiding, Overloading >
Siva Nookala - 14 Mar 2016
Method overriding is a powerful concept supported by Java, which helps in changing the behavior of the method implemented in the super-class. The program Inheritance Example Program To Remove Duplicate Code is changed to see how we can use the same method name in both the super-class and sub-class.

Icecream Prices Using Method Overriding
class IceCreamPricesWithOverriding
{
    public static void main(String arg[])
    {
        IceCream ic = new IceCream();
        ic.flavor = "Pista";
        ic.numberOfScoops = 2;
        
        System.out.println(ic.numberOfScoops + " scoops of " + ic.flavor + " flavor price is : " + ic.getPrice());
        
        FruitSaladWithIceCream fs = new FruitSaladWithIceCream();
        fs.flavor = "Chocolate";
        fs.numberOfScoops = 1;
        fs.gramsOfFruitSalad = 50;
        
        System.out.print(fs.gramsOfFruitSalad + " grams of fruit salad and ");
        System.out.println(fs.numberOfScoops + " scoops of " + fs.flavor + " flavor price is : " + fs.getPrice());
        
        KhubaniKaMeetaWithIceCream kkm = new KhubaniKaMeetaWithIceCream();
        kkm.flavor = "Vanila";
        kkm.numberOfScoops = 1;
        kkm.gramsOfKhubaniKaMeeta = 75;
        
        System.out.print(kkm.gramsOfKhubaniKaMeeta + " grams of khubani ka meeta and ");
        System.out.println(kkm.numberOfScoops + " scoops of " + kkm.flavor + " flavor price is : " + kkm.getPrice());
    
    }
}

class IceCream
{
    String flavor;
    int numberOfScoops;
    
    double getPrice()
    {
        double pricePerScoop = 35.0;
        return numberOfScoops * pricePerScoop;
    }
}

class FruitSaladWithIceCream extends IceCream
{
    int gramsOfFruitSalad;

    double getPrice()
    {
        double iceCreamPrice = super.getPrice(); // LINE A
        double pricePerGram = 0.75;

        return gramsOfFruitSalad * pricePerGram + iceCreamPrice;
    }
}

class KhubaniKaMeetaWithIceCream extends IceCream
{
    int gramsOfKhubaniKaMeeta;

    double getPrice()
    {
        double iceCreamPrice = super.getPrice(); // LINE B
        double pricePerGram = 1.25;

        return gramsOfKhubaniKaMeeta * pricePerGram + iceCreamPrice;
    }
}
OUTPUT

2 scoops of Pista flavor price is : 70.0
50 grams of fruit salad and 1 scoops of Chocolate flavor price is : 72.5
75 grams of khubani ka meeta and 1 scoops of Vanila flavor price is : 128.75

DESCRIPTION

In this program similar to Inheritance Example Program To Remove Duplicate Code we have created 3 classes - IceCream, FruitSaladWithIceCream and FruitSaladWithIceCream. But the name of the method which gives the price is same for all of them. The method is called getPrice. This program also uses the super keyword to distinguish between the getPrice method of the sub-class and the super-class.

THINGS TO TRY
  • Define a new class BadamMilkWithIceCream which extends from IceCream and add member variable milliLitersOfBadamMilk and add a method getPrice which calls super.getPrice() to get the price of the ice cream. Assume that the price of milli liter of badam milk is Rs. 0.20.
As shown in the above program a method with the same name can be defined in both the super-class and the sub-class. The getPrice method is defined in IceCream class as well as FruitSaladWithIceCream. The method signature (method name, parameters and the return type) is exactly same for both the methods. Creating a method with the same method signature as the super-class method is called method overriding.
When a method is overridden, but we still want to use the super-class implementation in the sub-class, we can use the super keyword to call that implementation. As shown in LINE A and LINE B of the above program, the super class's implementation of getPrice is called using super.getPrice().
Method overriding is further explained with another example in How A Method Can Be Overridden In Different Ways .
The concept of Method Overloading In Java is different from method overriding, the differences are explained in Method Overloading Vs Method Overriding.

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