Design Patterns For Dummies®

Chapter 5. From One to Many: The Singleton and Flyweight Patterns

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Using the Singleton pattern

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Creating singletons

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Synchronizing to avoid multithreading issues

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Handling multithreading issues a better way

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Using the Flyweight pattern

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In your capacity as highly paid consultant to MegaGigaCo, you’re troubleshooting some performance issues. “Everything just goes really slowly,” say the company programmers.

“Hmm,” you say, “I notice you have a really big database object, about 20 megabytes.”

“Yep,” they say.

“How many of these objects do you have at any one time?”

“About 219,” the company programmers say.

“So you have 219 20-megabyte objects when your code is running?” you ask. “Does anyone see a problem with that?”

“Nope,” they say.

You tell them, “You’re using too many system resources. You’ve got hundreds of huge objects that you’re expecting the computer to handle. Do you really need all those objects?”

“Well. . . . ,” they say.

“I thought not,” you say. “I’ll fix your problem using the Singleton design pattern. For a few megabucks.”

“Hmm,” they say, “now it’s you that’s straining the system resources.”

This chapter is about taking control of the number of objects you have floating around in your code. There are two patterns especially helpful here: the Singleton design pattern and the Flyweight design pattern.

With the Singleton ...