Design Patterns Tutorial

Learn Design Patterns Step by Step

Build maintainable, flexible, and reusable software by understanding common design patterns through practical Java examples.

Learning path: Start with object creation, continue with class and object composition, and finish with communication and behavior between objects.

Design Pattern Categories

Explore 23 commonly used design patterns grouped by the problem they solve in an application.

Creational Design Patterns

Singleton

Ensure a class has one shared instance and provide a controlled way to access it.

Factory Method

Create objects through a method so implementations can decide which object to return.

Abstract Factory

Create families of related objects without coupling code to concrete classes.

Builder

Construct complex objects step by step while keeping creation readable and flexible.

Prototype

Create new objects by copying an existing configured object.

Structural Design Patterns

Adapter

Make incompatible interfaces work together without changing existing classes.

Bridge

Separate an abstraction from its implementation so both can evolve independently.

Composite

Treat individual objects and groups uniformly through a tree structure.

Decorator

Add responsibilities dynamically without changing the original class.

Facade

Provide a simple interface to a larger subsystem.

Flyweight

Share reusable state to reduce memory use for similar objects.

Proxy

Control access to another object for lazy loading, security, caching, or remote calls.

Behavioral Design Patterns

Chain of Responsibility

Pass a request through a sequence of handlers until one can process it.

Command

Encapsulate a request as an object so it can be queued, logged, undone, or parameterized.

Interpreter

Represent and evaluate simple language rules using an object-based grammar.

Iterator

Traverse a collection without exposing its internal representation.

Mediator

Centralize communication between objects to reduce direct dependencies.

Memento

Capture and restore object state without exposing implementation details.

Observer

Notify dependent objects when a subject's state changes.

State

Allow an object to change behavior when its internal state changes.

Strategy

Define interchangeable algorithms and select one at runtime.

Template Method

Define an algorithm skeleton while subclasses customize selected steps.

Visitor

Add operations to object structures without modifying their classes.