Grokking Design Patterns for Engineers and Managers
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For quick reference, the following table offers a thorough analysis of the distinctive characteristics, applicability, examples, benefits, and drawbacks of each behavioral design pattern.

Pattern NameDistinctive FeatureApplicabilityAn ExampleProsCons
IteratorProvides a way to access elements of a collection sequentially without exposing its underlying representationWhen you need to provide a standard way to traverse through a collection without exposing its implementationBrowsing through a playlistSimplifies client code and hides complexity of the collectionIterator state management can be complex
StrategyEnables an algorithm's behavior to be selected at runtimeWhen there are multiple ways to achieve a task and you want to determine the algorithm at runtimeDifferent compression algorithmsFlexibility to switch algorithms; isolation of algorithm implementationComplexity due to additional classes; clients must be aware of different strategies
Template MethodDefines the skeleton of an algorithm in an operation, deferring some steps to subclassesWhen the core structure of an algorithm should not change, yet some steps are open to being overriddenFrameworks defining application structurePromotes code reuse and enforces a predefined algorithm structureCan lead to less flexibility in subclasses; harder to maintain
ObserverNotifies multiple objects about state changesWhen changes in one object's state require other objects to be notifiedReal-time data feedsLoose coupling between subject and observersRisk of unintended performance issues
CommandEncapsulates a request as an objectFor operations that need to be executed, undone, or loggedUser actions in GUI applicationsDecouples command execution from usageCan lead to numerous concrete command classes
StateAllows objects to alter their behavior when their internal state changesFor objects whose behavior depends on their state and can change at runtimeDifferent modes in a gameLocalizes state-specific behaviorsIncreases the number of classes
Chain of ResponsibilityDelegates commands to a chain of processing objectsFor scenarios where multiple objects can handle a request, but the handler is unknownHelp systems in applicationsDecouples request sender and receiverHandling can become inefficient
MediatorCentralizes complex communications between related objectsTo reduce direct communications between multiple objectsChat applicationSimplifies interactions between groups of objectsMediator can become overly complex
MementoCaptures and externalizes an object's internal stateFor undo functionality or state save-and-restoreUndo feature in editorsPreserves encapsulation boundariesCan be memory-intensive
VisitorSeparates an algorithm from the objects on which it operatesWhen operations need to be performed on a group of similar kinds of objectsProcessing different types of document elements in a word processorSimplifies adding new operations; centralizes related operationsCan lead to a bloated visitor interface; harder to maintain when the object structure changes

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