how flyweight design pattern minimizes memory

Question

How does the Flyweight design pattern minimizes memory used? For me it looks like instead of creating objects it is only externalizing the data held by object which means memory used is the same.

Am I missing anything ?

Answer 1

The idea behind the flyweight pattern is that you have a small object that points to shared data.

That is, more than one instance of the object shares the data.

If there is only one object for each data it will indeed not use less memory, but instead more, since you now have the data and a pointer pointing to said data.

Answer 2

Alignment and hidden state. Objects in most OO languages have to be aligned at at least 8-byte boundary. A 32-bit processor can only efficiently access data at a 4-byte boundary. The extra space is used to store a hidden class pointer (4 byte) for each object in addition to the objects own data. Two objects representing a bit then take at least 16 bytes. On 64-bit processors it is often 16-byte alignment.

In some OO languages value objects are used to handle common cases like small integers. Smalltalk implementations have 31 bit small integers and use the extra bit to indicate that this is the case.

Answer 3

Quoting from http://www.oodesign.com/flyweight-pattern.html

The intent of this pattern is to use sharing to support a large number of objects that have part of their internal state in common where the other part of state can vary.

Wiki article Flyweight

Flyweight is a software design pattern. A flyweight is an object that minimizes memory use by sharing as much data as possible with other similar objects; it is a way to use objects in large numbers when a simple repeated representation would use an unacceptable amount of memory.