Java: Factory Method Pattern
A Creational Design Pattern
Before you start, heads up to here for the simple introduction to the design patterns and the index to all the design patterns deep tutorials.
Defined
- Factory method is a creational pattern that uses factory methods to deal with the problem of creating objects without having to specify the exact class of the object that will be created.
- It provides a way to delegate the instantiation logic to child classes.
Why, When?
- Useful when it doesn’t know what exact sub-class will be required during execution.
- Factory method pattern can be used when there is common/generic implementation in a class but the required sub-class is decided dynamically during runtime.
Enough, Show me something
Following example is all you need to understand this design pattern.
We need to have a super class wheel.
Super class in factory design pattern can be an interface, abstract class or a normal java class. We are using abstract class in our example.
Now, we have two sub-classes CarWheel and BikeWheel as below.
Notice that both the class extends Wheel class.
Now that we have super classes and sub-classes ready, we can write our factory class. Here is the basic implementation.
We are ready with super class and sub-class, we can have a factory class: WheelFactory
Let’s have a test drive: TestWheelFactory class
And that’s it. Really! Go, try this.
Code: Find the code used in this article on github.
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