9 crucial Java Design Principles you cannot miss

9 crucial Java Design Principles you cannot miss

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  1/9 What isEncapsulation ? Much of object programming is centered on minimizing the ripple effects caused by changes to a program. This is done simply by keeping details secret The principal ways of doing this are: - minimizing visibility - private fields, package-private classes (grouping into 1 domain package: entity,repository,service,controller) - generic references (polymorphism) - using high level references (interfaces or abstract classes) instead of low level references (concrete classes)
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  2/9 What isPolymorphism ? The point of polymorphism is that you can subclass a class and the objects implementing those subclasses will have different behaviors for the same methods defined in the superclass (and overridden in the subclasses).
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  3/9 What isAggregation / Composition ? has-a relationship
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  4/9 What isMethod Overloading ? If a class has multiple methods by same name but different parameters
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  5/9 Inheritance vsCompositions ? inheritance - Java doesnt support multiple inheritance (till java 8 , where we have default methods ) composition - Use private members inh - you need super class instance comp - easy to create Mock Object representing composed class inh - it breaks encapsulation, when behavior of super class changes, functionality in sub class may get broken comp - you are flexible enough to replace implementation of Composed class with better and improved version. inh - Inheritance makes much sense like when a genuine parent child relation exists comp - In Decorator pattern, we dont extend any class to add additional functionality Instead we keep an instance of the class we are decorating and delegates original task to that class after doing decoration
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  6/9 What isDRY ? avoid duplication for functionality , use dependency injection if needed. but you can repeat same code (ie user authorization) for different functionalities in micro services or micro functionalities
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  7/9 What isDependency Injection ? Class injected by DI framework is easy to test with mock object Easier to maintain because object creation code is centralized in framework Done in Spring via proxies
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  8/9 What isDelegation ? delegate tasks to ie: equals, hashcode methods, thread pools do not do it yourself on client side
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  9/9 What isLaw of Demeter / Principle of least knowledge ?