Design Pattern

Design Pattern

1. Creational Pattern

   • Factory
     • Factory design pattern is used when we have a super class with multiple sub-classes and based on input, we need to return one of the sub-class. This pattern take out the responsibility of instantiation of a class from client program to the factory class
       • NumberFormat.getInstance()
   • Abstract Factory
     • get rid of if-else block and have a factory class for each sub-class and then an Abstract Factory class that will return the sub-class based on the input factory class
   • Singleton
     • Singleton pattern restricts the instantiation of a class and ensures that only one instance of the class exists in the java virtual machine. The singleton class must provide a global access point to get the instance of the class.
       • Java Synchronization
         • http://www.journaldev.com/1061/java-synchronization-and-thread-safety-tutorial-with-examples
         • Volatile keyword
         • Synchronize keyword
         • Atomic Wrapper class
         • Locks
         • safe collection classes
   • Builder
     • build the object step-by-step and provide a method that will actually return the final Object.
       • StringBuilder.append()
   • Prototype
     • Prototype pattern is used when the Object creation is a costly affair and requires a lot of time and resources and you have a similar object already existing. So this pattern provides a mechanism to copy the original object to a new object and then modify it according to our needs

2. Structural Pattern

   • Adapter
     • its used so that two unrelated interfaces can work together
   • Composite
     • When we need to create a structure in a way that the objects in the structure has to be treated the same way, we can apply composite design pattern.
   • Facade
     • Provide a unified interface to a set of interfaces in a subsystem. Facade Pattern defines a higher-level interface that makes the subsystem easier to use.
   • Decorator
     • used to modify the functionality of an object at runtime

3. Behavior Pattern

   • Observer
     • Define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically