Java Design Pattern

1. Creational
   • Prototype - A fully initialized instance to be copied or cloned. Ex - Chess board.
   • Builder - Seperate object construction from its representation. Ex - Menu of any restaurant
   • Singleton - A class of which only a single instance can exist. Ex - President of country, Database connection, Logging
   • Factory method - Creates a factory of object types. Ex - Shape factory that generates different shapes.
2. Structural
   • Proxy - An object representing another object. Ex - Credit card, Debit card
   • Decorator - Add responsibilities to the object dynamically. Ex - Adding discount on order, Adding toppings on pizza, Java IO.
   • Facade - A single class that represent an entire subsystem. Ex - Event manager, Online booking order.
   • Adapter - Match interfaces of different class. Ex - Power adapter.
   • Flyweight - A fine grained instance used for efficient sharing. Ex - Public switched network, JDBC Connection pooling.
3. Behavioural
   • Chain of resposibility - A way of passing a request between chain of objects. Ex - Exception handling in Java.
   • Iterator - Sequentially access elements of a collection. Ex - Iterator class, next and prev button on Tv remote.
   • State - Alter an object behaviour when its state changes. Ex - Fan wall control
   • Strategy - Encapsulate an algorithm inside a class. Ex - Sorting based on different algorithms.
   • Observer - A way of notifying a change to number of classes. Ex - Newspaper
   • Visitor - Define a new operation to a class without change. Ex - Operation of a taxi company.
   • Template method - Defer an exact steps of an algorithm to a sub class. Ex - House plan.
   • Command - Encapsulate a command request as a object. Ex - Runnable interface, Waiter take order and pass it to cook.
   • Memento - Capture and restore object's internal state. Ex - Serialization, Undo/Redo.
   • Mediator - Defines simplified communication between classes. Ex - Air traffic controller.