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Design patterns are well-proven solutions for solving specific problems/tasks. Design patterns are programming language independent strategies for solving the common object-oriented design problems. That means, a design pattern represents an idea, not a particular implementation.
Factory pattern is one of the most used design patterns in Java. In Factory pattern, we create object without exposing the creation logic to the client and refer to newly created object using a common interface.
Abstract Factory patterns work around a super-factory which creates other factories. This factory is also called as factory of factories. In Abstract Factory pattern an interface is responsible for creating a factory of related objects without explicitly specifying their classes. Each generated factory can give the objects as per the Factory pattern.
Singleton pattern is one of the simplest design patterns in Java. This pattern involves a single class which is responsible to create an object while making sure that only single object gets created. This class provides a way to access its only object which can be accessed directly without need to instantiate the object of the class.
Builder pattern builds a complex object using simple objects and using a step by step approach. A Builder class builds the final object step by step. This builder is independent of other objects.
Prototype pattern refers to creating duplicate object while keeping performance in mind. This pattern involves implementing a prototype interface which tells to create a clone of the current object. This pattern is used when creation of object directly is costly. For example, an object is to be created after a costly database operation. We can cache the object, returns its clone on next request and update the database as and when needed thus reducing database calls.
Adapter pattern works as a bridge between two incompatible interfaces. This pattern involves a single class which is responsible to join functionalities of independent or incompatible interfaces. A real life example could be a case of card reader which acts as an adapter between memory card and a laptop. You plugin the memory card into card reader and card reader into the laptop so that memory card can be read via laptop. We are demonstrating use of Adapter pattern via following example in which an audio player device can play mp3 files only and wants to use an advanced audio player capable of playing vlc and mp4 files.
Bridge is used when we need to decouple an abstraction from its implementation so that the two can vary independently. This pattern involves an interface which acts as a bridge which makes the functionality of concrete classes independent from interface implementer classes. Both types of classes can be altered structurally without affecting each other.