Design Patterns in Java

What Are Design Patterns? Design patterns are reusable solutions to common problems in software design. They are not finished code you copy and paste. They are templates ...

The Singleton Pattern The Singleton pattern restricts a class to a single instance and provides a global point of access to it. It is one of the most well-known patterns, but also ...

The Factory Method Pattern The Factory Method pattern defines an interface for creating an object, but lets a parameter or subclass decide which class to instantiate. Instead of ...

The Abstract Factory Pattern The Abstract Factory pattern provides an interface for creating families of related objects without specifying their concrete classes. Where the ...

The Builder Pattern The Builder pattern separates the construction of a complex object from its representation. Instead of forcing callers through a constructor with many ...

The Prototype Pattern The Prototype pattern creates new objects by copying an existing object - the prototype - instead of building them from scratch. When construction is ...

The Adapter Pattern The Adapter pattern translates one interface into another so that classes that could not work together can collaborate. It sits between a client that expects a ...

The Facade Pattern The Facade pattern hides a complex subsystem behind one simple interface. You give callers a single, friendly class that internally coordinates dozens of moving ...

The Proxy Pattern The Proxy pattern provides an object that stands in for another object. It controls how, when, and whether the real object is reached, while keeping the same ...

The Decorator Pattern The Decorator pattern attaches extra behaviour to an object without changing its class. You wrap an object in one or more layers, each adding a small ...

The Composite Pattern The Composite Pattern lets you treat individual objects and groups of objects the same way. Instead of writing separate code for a single item and a ...

The Strategy Pattern The Strategy Pattern defines a family of algorithms, encapsulates each one, and makes them interchangeable at runtime. Instead of hard-coding a single ...

The Template Method Pattern The Template Method Pattern defines the skeleton of an algorithm in a base class but lets subclasses override specific steps without changing the ...

The Observer Pattern The Observer Pattern establishes a one-to-many dependency between objects so that when one object (the subject) changes state, all its dependants (observers) ...

The Command Pattern The Command Pattern encapsulates a request as an object, thereby letting you parameterize clients with different requests, queue or log requests, and support ...

The State Pattern The State pattern allows an object to alter its behaviour when its internal state changes. The object appears to change its class at runtime. Instead of writing ...

Chain of Responsibility and Mediator Patterns The Chain of Responsibility pattern lets you pass a request along a chain of handlers. Each handler decides either to process the ...

Iterator, Memento and Flyweight Patterns These three patterns address very different concerns but share a common goal: they hide complexity from the client code. The Iterator ...

Design Patterns in Spring and Modern Frameworks Design patterns are not just textbook theory. The frameworks you use every day are built on top of them. Understanding which ...

Anti-Patterns and How to Choose the Right Pattern Knowing design patterns is only half the battle. Knowing when NOT to use them is equally important. An anti-pattern is a practice ...