A Practical Introduction to Data Structures and Algorithm Analysis

Sec. 1.3 Design Patterns 13Data TypeADT:• Type• OperationsData Items:Logical FormData Structure:• Storage Space• SubroutinesData Items:Physical FormFigure 1.1 The relationship between data items, abstract data types, and datastructures. The ADT defines the logical form of the data type. The data structureimplements the physical form of the data type.designers learn and reuse various techniques for combining software components.Such techniques are sometimes referred to as design patterns.A design pattern embodies and generalizes important design concepts for arecurring problem. A primary goal of design patterns is to quickly transfer theknowledge gained by expert designers to newer programmers. Another goal is toallow for efficient communication between programmers. Its much easier to discussa design issue when you share a vocabulary relevant to the topic.Specific design patterns emerge from the discovery that a particular designproblem appears repeatedly in many contexts. They are meant to solve real problems.Design patterns are a bit like generics: They describe the structure for adesign solution, with the details filled in for any given problem. Design patternsare a bit like data structures: Each one provides costs and benefits, which impliesthat tradeoffs are possible. Therefore, a given design pattern might have variationson its application to match the various tradeoffs inherent in a given situation.The rest of this section introduces a few simple design patterns that are usedlater in the book.1.3.1 FlyweightThe Flyweight design pattern is meant to solve the following problem. You havean application with many objects. Some of these objects are identical in the informationthat they contain, and the role that they play. But they must be reachedfrom various places, and conceptually they really are distinct objects. Because somuch information is shared, we would like to take advantage of the opportunity toreduce memory cost by sharing space. An example comes from representing the