The Geek's Blog

Primitive Obsession is the name of a code smell that occurs when we use primitive data types to represent domain ideas. For example, we use a string to represent a message or an integer to represent an amount of money. For Example: Code with Primitive Obsession // primitiveObsession.java public class primitiveObsession { public static void main ( String args []) { Integer [] cityPopulations = { 13000000 , // London 21903623 , // New York 12570000 , // Tokyo 1932763 , // Stockholm 1605602 , // Barcelona 4119190 // Sydney }; for ( Integer cityPopulation : cityPopulations ) { System . out . println ( cityPopulation ); } } } public class City { private final String name ; private final int population ; private final Continent continent ; public String getName () { return name ; } public int getPopulation () { return population ; } public Continent ge...

This pattern is used when it must be decided at run time which one of several compatible classes is to be instantiated. For example, the abstract Collator class's getInstance() method returns a collation object that is appropriate for the default locale, as determined by java.util.Locale.getDefault() : Like other locale-sensitive classes, you can use the static factory method, getInstance, to obtain the appropriate Collator object for a given locale.  The following example shows how to compare two strings using the Collator for the default locale. Compare two strings in the default locale Collator myCollator = Collator.getInstance(); if( myCollator.compare("abc", "ABC") < 0 ) System.out.println("abc is less than ABC"); else System.out.println("abc is greater than or equal to ABC");

Lazy Initialization :- The instantiation of an object can be delayed until it is actually needed. Usage: This especially beneficial when the constructor is doing a costly job like, accessing a remote database. Example: This code demonstrates how the Singleton pattern can be used to create a counter to provide unique sequential numbers, such as might be required for use as primary keys in a Database:   Sequence.java   public class Sequence { private static Sequence instance; private static int counter; private Sequence() { counter = 0; // May be necessary to obtain // starting value elsewhere... } public static synchronized Sequence getInstance() { if(instance==null) // Lazy instantiation { instance = new Sequence(); } return instance; } public static synchronized int getNext() { return ++counter; } }   Some things to note about this implementation: Synchronized methods are used to ensure that the class is thread-safe. This class cannot be subclassed because the constructor is private ...

The pattern is an organised way of solving some specific class of problems. These patterns come in to the picture at analysis and high-level-design phase. The first step of applying one pattern to the code base is first to understand the find the vector of change in the code base. Next step is to isolate the things that are subject to change form the things that are not. That is adding a layer of abstraction to the code. The goal of design patterns is isolating the changes in your code. Understand Inheritance and Composition as a solution to a specific class of problems. Inheritance : - It allows you to express differences in behavior (that's the thing that changes) in objects that all have the same interface (that's what stays the same). Composition : - Composition can also be considered a pattern, since it allows you to change—dynamically or statically—the objects that implement your class, and thus the way that class works. Some principles of designing the c...