Design Patterns

• Cargo Cult ProgrammingCopying code or rituals without understanding why they work.
• Spaghetti CodeTangled control flow that's impossible to follow.
• MiddlewareA pipeline of functions wrapped around request handling.

Core: start here

• Dependency InjectionPassing dependencies in instead of creating them inside.

• Domain ModelOrganizing business logic as objects that hold both data and behavior.
• BridgeSeparating an abstraction from its implementation so both can vary.
• Data MapperA separate layer moving data between objects and the database.
• FlyweightSharing common state among many small objects to save memory.
• MediatorCentralizing communication between objects.
• Service LocatorA registry for looking up dependencies, often seen as an anti-pattern.
• Abstract FactoryCreating families of related objects without naming concrete classes.
• Identity MapEnsuring each database row is loaded into only one object per session.
• MementoCapturing state so it can be restored later, as in undo.
• Patterns of Enterprise Application ArchitectureFowler's catalog: transaction script, domain model, data mapper and more.
• PrototypeCreating objects by cloning an existing one.
• VisitorAdding operations to a structure without changing its classes.
• Type ObjectDefining "kinds" of things as data instead of subclasses.
• Unit of WorkTracking changes and committing them in one transaction.

• Blackboard PatternIndependent components cooperating through a shared knowledge store.

• Cargo Cult ProgrammingCopying code or rituals without understanding why they work.
• Spaghetti CodeTangled control flow that's impossible to follow.

• Dependency InjectionPassing dependencies in instead of creating them inside.
• Design PatternA named, reusable solution to a recurring design problem.
• Finite State MachineA model with a fixed set of states and allowed transitions, e.g. an order going from paid to shipped.
• Anti-PatternA common solution that looks right but causes problems.
• Factory MethodLetting subclasses or functions decide which class to instantiate.
• SingletonEnsuring a class has exactly one instance; often an anti-pattern.
• StrategySwapping algorithms behind a common interface.

• Cargo Cult ProgrammingCopying code or rituals without understanding why they work.
• Spaghetti CodeTangled control flow that's impossible to follow.

• MiddlewareA pipeline of functions wrapped around request handling.
• AdapterWrapping an interface to make it match another.
• Dependency InjectionPassing dependencies in instead of creating them inside.
• Design PatternA named, reusable solution to a recurring design problem.
• Finite State MachineA model with a fixed set of states and allowed transitions, e.g. an order going from paid to shipped.
• Inversion of ControlA framework calls your code rather than your code calling it.
• Iterator PatternTraversing a collection without exposing its internals.
• Null ObjectA do-nothing object used instead of null checks.
• Template MethodA base algorithm whose steps subclasses fill in.
• Anti-PatternA common solution that looks right but causes problems.
• BuilderConstructing complex objects step by step.
• Chain of ResponsibilityPassing a request along handlers until one deals with it; how middleware works.
• CommandTurning a request into an object you can queue, log or undo.
• CompositeTreating individual objects and groups of them uniformly, as a tree.
• DecoratorAdding behavior to an object by wrapping it.
• FacadeA simple interface over a complex subsystem.
• Factory MethodLetting subclasses or functions decide which class to instantiate.
• Gang of FourThe 1994 book that catalogued 23 classic patterns.
• ObserverNotifying subscribers when something changes.
• ProxyA stand-in that controls access to another object.
• SingletonEnsuring a class has exactly one instance; often an anti-pattern.
• StateChanging an object's behavior when its internal state changes.
• StrategySwapping algorithms behind a common interface.
• Publish-SubscribeSenders publish to topics; receivers subscribe without knowing each other.

• BridgeSeparating an abstraction from its implementation so both can vary.
• FlyweightSharing common state among many small objects to save memory.
• MediatorCentralizing communication between objects.
• Service LocatorA registry for looking up dependencies, often seen as an anti-pattern.
• Abstract FactoryCreating families of related objects without naming concrete classes.
• MementoCapturing state so it can be restored later, as in undo.
• PrototypeCreating objects by cloning an existing one.
• VisitorAdding operations to a structure without changing its classes.
• Type ObjectDefining "kinds" of things as data instead of subclasses.