The Geek's Blog

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 ...