Factory

Learn the Factory pattern.

The Factory pattern

The Factory moves object creation to a central place. The client does not need to know which concrete class is created; it works only through an interface. This frees the code from depending on concrete classes.

Example: ShapeFactory.create("circle") returns a Shape; whether it is a Circle or another class does not concern the client. To add a new shape type you only change the factory method. This flexibility is especially valuable in large systems.

Interface and concrete classes

The foundation of a Factory is a common interface. The Shape interface declares a draw method; Circle and Square implement it. The factory returns the right concrete class based on a parameter.

So the client writes Shape s = factory.create("circle") and calls s.draw(); the concrete type stays hidden. Adding new concrete classes without changing the interface becomes easy, supporting the open-closed principle.

Exercise Create a shape with ShapeFactory

Define a Shape interface with void draw(). A Circle class implements it and prints circle with System.out.println inside draw. In ShapeFactory, a static Shape create(String type) method returns new Circle() when type is "circle". In main, get a shape with ShapeFactory.create("circle") and call draw.

Show example solution

interface Shape { void draw(); }

class Circle implements Shape {
    public void draw() { System.out.println("circle"); }
}

class ShapeFactory {
    public static Shape create(String type) {
        if (type.equals("circle")) return new Circle();
        return null;
    }
}

public class FactoryDemo {
    public static void main(String[] args) {
        Shape s = ShapeFactory.create("circle");
        s.draw();
    }
}

Test yourself

What does the Factory pattern hide?
- The data
- Which concrete class is created
- The method signature
- The interface
Show answer

Which concrete class is created — The Factory hides which concrete class is created from the client.
Match the Factory concepts

create("circle")

Factory method
Shape

Common interface
Circle

Concrete class
s.draw()

Client call

Complete the Factory call

Shape s = ShapeFactory.create(____);

Show answer

Shape s = ShapeFactory.create("circle");

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