Static Factory Method Pattern

Static Factory Method Pattern - Example Implementation

Creating objects of DIFFERENT types

First, create a Polygon interface

interface Polygon {
    String getType();
}

Next, create a few Polygon implementations like Square, Triangle, etc

class Square implements Polygon { String getType() { return "square"; } }

class Triangle implements Polygon { String getType() { return "triangle"; } }

Static Factory Method Pattern implementation

public static Polygon polygonFactoryMethod(final int numberOfSides) {
    if (numberOfSides == 3) {
        return new Triangle();
    } else if (numberOfSides == 4) {
        return new Square();
    } else {
        throw new RuntimeException("invalid input");
    }
}

Use case

public static void main(String[] args) {
 	Polygon triangle = polygonFactoryMethod(3);
 	Polygon square   = polygonFactoryMethod(4);
    // ...
    System.out.println(triangle.getType()); // triangle
    System.out.println(square.getType());   // square
}

Creating objects of SAME type but with Different states

class Polygon {
	private String type;
	public Polygon(final String type) { this.type = type; }
    public String getType() { return type; }
}

public static Polygon polygonFactoryMethod(final int numberOfSides) {
    if (numberOfSides == 3) {
        return new Polygon("triangle");
    } else if (numberOfSides == 4) {
        return new Polygon("square");
    } else {
        throw new RuntimeException("invalid input");
    }
}

public static void main(String[] args) {
 	Polygon triangle = polygonFactoryMethod(3);
 	Polygon square   = polygonFactoryMethod(4);
    // ...
    System.out.println(triangle.getType()); // triangle
    System.out.println(square.getType());   // square
}

Comparisons

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Factory Method Pattern vs Static Factory Method Pattern

• Static Factory Method Pattern does not allow overriding
• Factory Method Pattern allows overriding for flexibility before compile time

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