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Lesson 5Flyweight: motivation
ObjectiveExplore the Motivations of the Flyweight Pattern

Flyweight Pattern and Motivation

In the realm of software architecture, one of the paramount concerns is the efficient utilization of resources, particularly when dealing with a large number of almost similar objects that have significant memory footprints. It is in this context that the Flyweight Pattern emerges as not merely an option but a necessity for any architect aiming for scalable and efficient systems. This design pattern serves to optimize memory usage and performance by sharing and reusing object data, thereby accomplishing the dual objective of resource conservation and operational efficiency. The motivation behind employing the Flyweight Pattern can be articulated under several key tenets:

Memory Efficiency

In scenarios where a system is burdened with a multitude of similar objects, the memory overhead can become a considerable challenge. The Flyweight Pattern mitigates this by sharing common state among multiple objects instead of keeping the state for each object. Imagine, for instance, a text editor that needs to represent each character as an object. Instead of creating individual objects for each occurrence of characters, the Flyweight Pattern would allow you to create a single object for each unique character, thus dramatically reducing memory consumption.

Improved Performance

The benefits are not just confined to memory optimization; the pattern also offers performance advantages. By reducing the number of unique objects, instantiation overhead is lowered, accelerating the object creation process. This speed gain is invaluable in real-time applications and large-scale systems where performance is of the essence.


As systems grow in complexity and data volume, scalability becomes a non-negotiable feature. The Flyweight Pattern inherently supports scalability by minimizing resource usage. When dealing with an increasingly large set of objects, the pattern ensures that the system remains responsive and capable of handling additional load without a proportional increase in resource consumption.

Consistency and Maintainability

When objects share common states, maintaining and updating the system becomes inherently easier. Any change to the shared state is automatically reflected across all instances that use the shared flyweight object. This consistency ensures that system behavior remains uniform, thereby simplifying maintenance tasks and reducing the likelihood of bugs and inconsistencies.

Facilitation of Complex Operations

The Flyweight Pattern provides a framework to handle complex operations efficiently. By externalizing the state and behavior of objects, the pattern allows you to manipulate many objects at once based on shared states. This capability is essential for operations like batch processing and bulk data manipulation.
In conclusion, the Flyweight Pattern is an indispensable tool for software architects striving for optimized, scalable, and maintainable systems. Its strategic adoption can provide substantial gains in memory efficiency, computational performance, and system scalability. Moreover, its utility extends to enhancing maintainability and facilitating complex operations, marking it as an imperative choice for architects aiming for robust, resource-efficient solutions. The judicious implementation of the Flyweight Pattern is not just a best practice; it is a strategic enabler of high-quality software architecture.
Object-oriented systems have a reputation for being big and slow. To some extent, this is a result of early, not particularly well-optimized implementations. Smalltalk, C++, and Java were all extremely slow in their early incarnations and produced multimegabyte executables for even simple Hello World-like programs. More sophisticated runtime environments and compiler optimizations have gone a long way toward removing the performance overhead associated with objects. However, it is still the case that in practice, object-oriented programming does not always produce the fastest code possible. If the objects in question are immutable (that is, they never change after they are constructed), and there are a relatively small number of states that the objects can assume, it may be possible to radically reduce the total number of objects in the system by using only copies of a few preconstructed objects.
For example, a Character class for a word processor might have only 200 or so instances (the lower and uppercase letters, assorted punctuation marks, white space, digits, and a few others). A 20, 000-character document might simply contain a list of 20,000 pointers to the 200 individual objects rather than 20,000 separate objects. If the pointers are much smaller or much faster to work with than the objects themselves (as they often are in practice) the memory footprint of a document can be reduced by a factor of 100 or more with a corresponding increase in performance. The Flyweight pattern does exactly this.

Flyweight Pattern

The Flyweight pattern describes how to share objects to allow their use at fine granularities without prohibitive cost. Each object of the flyweight pattern is divided into two pieces:
  1. the state-dependent (extrinsic) part, and
  2. the state-independent (intrinsic) part.
Intrinsic state is stored in the Flyweight object. Extrinsic state is stored or computed by client objects, and passed to the Flyweight when its operations are invoked.

States of the Flyweight Pattern

The Flyweight pattern divides the application's state into two parts: **intrinsic state** and **extrinsic state**.
  1. Intrinsic state is the part of the state that is shared by multiple objects. It is typically constant or read-only.
  2. Extrinsic state is the part of the state that is unique to each object. It is typically volatile or mutable.

The Flyweight pattern works by creating a pool of flyweight objects, each of which represents a unique intrinsic state. When a client needs an object with a specific intrinsic state, it checks the pool to see if an existing flyweight object can be reused. If so, the client reuses the existing flyweight object. Otherwise, the client creates a new flyweight object and adds it to the pool. The client passes the extrinsic state to the flyweight object when it calls its methods. The flyweight object uses the extrinsic state to perform its operations. The Flyweight pattern can be used to reduce memory usage and improve performance in applications that use a large number of objects with similar state.
Here is an example of the Flyweight pattern:
A text editor uses the Flyweight pattern to represent the characters in a document. Each character is represented by a flyweight object. The flyweight objects store the intrinsic state of the character, such as its font and font size. The client code (the text editor) passes the extrinsic state of the character to the flyweight object when it needs to draw the character on the screen. The extrinsic state of the character includes its position on the screen and its color. By using the Flyweight pattern, the text editor can avoid creating a separate object for each character in the document. This can significantly reduce memory usage and improve performance.
Here is a diagram of the Flyweight pattern:
| Flyweight |
   | intrinsic state
   | extrinsic state
	   | client code

The Flyweight pattern is a powerful design pattern that can be used to improve the performance and scalability of applications.