What is a factory pattern?

A Factory method pattern (aka Factory pattern) is a creational pattern. The creational patterns abstract the
object instantiation process by hiding how the objects are created and make the system independent of the object creation process. An Abstract factory pattern is one level of abstraction higher than a factory method pattern, which means it returns the factory classes.

public interface Const {
public static final int SHAPE_CIRCLE =1;
public static final int SHAPE_SQUARE =2;
public static final int SHAPE_HEXAGON =3;
}
public class ShapeFactory {
public abstract Shape getShape(int shapeId);
}
public class SimpleShapeFactory extends
ShapeFactory throws BadShapeException {

public Shape getShape(int shapeTypeId){
Shape shape = null;
if(shapeTypeId == Const.SHAPE_CIRCLE) {
//in future can reuse or cache objects.
shape = new Circle();
}
else if(shapeTypeId == Const.SHAPE_SQUARE) {
//in future can reuse or cache objects
shape = new Square();
}
else throw new BadShapeException
(“ShapeTypeId=”+ shapeTypeId);
return shape;
}
}


Now let’s look at the calling code, which uses the
factory:
ShapeFactory factory = new SimpleShapeFactory();
//returns a Shape but whether it is a Circle or a
//Square is not known to the caller.
Shape s = factory.getShape(1);
s.draw(); // circle is drawn
//returns a Shape but whether it is a Circle or a
//Square is not known to the caller.
s = factory.getShape(2);
s.draw(); //Square is drawn