Builder Vs Decorator pattern [closed]

Answer 1

Lets go through key characteristics of Builder and Decorator.

Builder: ( A Creational pattern)

1. Too Many arguments to pass from client program to the Factory class that can be error prone
2. Some of the parameters might be optional unlike in Factory which forces to send all parameters
3. Object is heavy and its creation is complex. e.g. building various types of pizzas

Decorator: ( A Structural pattern)

1. Add behaviour to object at run time. Inheritance is the key to achieve this functionality, which is both advantage and disadvantage of this pattern.
2. It enhances the behaviour of interface.
3. Decorator can be viewed as a degenerate Composite with only one component. However, a Decorator adds additional responsibilities - it isn't intended for object aggregation.
4. Decorator supports recursive composition
5. Decorator is designed to let you add responsibilities to objects without sub-classing

When to use Decorator:

1. Object responsibilities and behaviours should be dynamically added/removed
2. Concrete implementations should be decoupled from responsibilities and behaviours
3. When sub - classing is too costly to dynamically add/remove responsibilities

Coming back to your query:

Builder is right creational pattern for Pizza. Pizza is created with mandatory ingredients initially ( Bread etc). Cheese, Pepperoni, Bacon are optional ingredients but still they can be part of pizza during build process.

Decorator is useful for adding dynamic responsibilities at run-time for already created object.

e.g. :

BufferedInputStream bis = new BufferedInputStream(new FileInputStream(new File("a.txt")));

Refer to below posts for more details:

Keeping builder in separate class (fluent interface)

When to Use the Decorator Pattern?