Yogesh's Tech Blog

As part of Generics , Java language supports type safe programming. It allows a type or method to operate on objects of various types while providing compile-time type safety. The most common use case is while using Java Collection framework. For example if you define a list of string and trying to add integer value to the list, compiler throws error. List list = new ArrayList(); //Compilation Error : he method add(int, String) in the type List is not applicable for the arguments (int) list.add(10); As a developer you may always notice redundancy in defining parameter type information in both the side of declaration. As off Java 1.6, language doesn’t provide any feature to overcome it. Using Static Factory : One possible way to overcome this problem by using static factory methods. If you frequently use typed list or map in application then you can define generic static factory methods which returns you required typed map or list. public static HashMap getMapInstance(){ ...

Many time we have static fields in our Java classes. These fields are get initialized with loading of your classes and all other static fields. But many time its not the urgent to initialize few of the fields while loading the class itself. Here the concept of lazy initialization comes in picture. Consider the code below public class LazyInitilaizationTest { public static String[] field = getStringContent(); static { System.out.println( "Loading Class" ); } public static String[] getStringContent(){ System.out.println( "Initializing field" ); return new String[]{}; } public static void main(String[] args) { System.out.println( "Accessing Field" ); System.out.println(field); } } Here the class has private & static field which gets initialized by invoking getStringContent () method. Running above class prints following output Initializing field Loading Class Acce...

First thing comes in mind when somebody say Non-extendable class , that is final class. Marking a class as “final” , no one can extends the particular class. But there is another tricky way to restricting any other class from extending your class. Thinking how ….? Simple, marking all available constructors of  a class as private. As per constructor chaining principle in class hierarchy , every child class constructor should delegate call to super class explicitly or implicitly. In implicit case, call get delegate to class’s default constructor. If all available constructors of the class are private then no other class can not extend it. 1: public class MyClass { 2: 3: private MyClass(){ 4: System.out.println(" Inside Singleton Constructor "); 5: } 6: 7: } 8: 9: class MyChildClass extends MyClass{ // compilation error 10: 11: }

I have explained two different implementation for making a class to Singleton, means restricting no of instance of a class to only one.You can refer previous posts Singleton Design Pattern by example & Alternative implementation for Singleton Class . Here by Static Class means a class that’s has only public static methods. Two different implementations as per previous post for restricting class instances to only one are making all constructor private referred as  Singleton  class and declaring all public methods as static.  Singleton class has several advantages over Static class pattern 1. A singleton class can extends class and implement interfaces , while Static class can not. 2. A singleton can be instantiated lazily or asynchronously while a static class is generally initialized when it is first loaded. 3.A singleton class can extended and its methods can be overridden. 4. The most important advantage is the singleton can be handled polymorphic ally withou...

Latest version of Java Enterprise Edition is focused on eae of development and simplicity. Key goals of this version are Extensibility – supports for additional technologies and frameworks Profiles – support for creating custom profiles based on application scope or requirement. Pruning New Features introduced in this edition are Simplified EJB 3.1 No local business interface – one step further from EJB 3.0 specification, EJB 3.1 specifications removes mandatory business interface Singleton EJB – to share application wide data and support concurrent access. EJB 3.1 can be part of war file directly without creating a separate jar file EAR >>       WAR >>             JSP/Static Pages             WEB_INF >>         ...

"Singleton designing pattern deals with a pattern in which instantiation of object is under control and restrict count by one by making constructor as private " "A Static mean a class that has only static members" A Singleton class is supposed to have one and only one instance while a static class is never instantiated . The singleton pattern has several advantage over the static class pattern A Singleton can extend class and implement interfaces, while a static class can not. A singleton can be initiated lazily or asynchronously while a static class is generally initialized when it is first loaded A singleton class can be extended and its methods overridden , We can not override static methods with non static method