Extreme Java

What are the steps followed before loading a class into memory?

admins — Mon, 21 May 2012 16:39:20 +0000

The steps followed by JVM to load a class into memory are: 1. The classes are loaded as and when they are referenced in a program. In case of inheritance, the super class is loaded before loading the sub class. 2. The static block of code is executed immediately after loading a class irrespective of [...]

What are the uses of this and super keywords?

admins — Mon, 21 May 2012 16:38:05 +0000

This keyword has multiple meanings. Used as reference variable: When used as a variable, it refers to the instance of the class on which the operation has been invoked. Example Code: Output: this.a: 10 In line 4 of the above program, this keyword refers to the instance created in line 9 of the program. Used [...]

What is reflection API?

admins — Mon, 21 May 2012 16:36:02 +0000

Reflection API is a reflection of an Object as created by using the new operator and as seen by JVM. Using this API, one can get information about an Object like its Constructors, Methods, Member variables etc. To get all this information, the Class object is required for any Object. The methods under this API [...]

What is a class loader and What are the different class loaders?

admins — Mon, 21 May 2012 16:34:51 +0000

A class loader is a program which loads the system/user defined classes. A class loader is generally a part of the compiler. Whenever a reference to a class is encountered and the class is found to be not yet loaded into the memory, the class loader loads the class into the memory so that all [...]

What is the best way to initialize references out of null, empty or uninitialized?

admins — Mon, 21 May 2012 16:33:07 +0000

Note: The word variable here refers to reference variables referring to objects and not primitive variables. Initializing the reference variables to proper value should not be ignored because it helps in avoiding the issues like NullPointerException and memory issues. If you don’t initialize the variables then either they will cause compiler error or will be [...]

What are the best practices for fetching large amount of data from database?

admins — Mon, 21 May 2012 16:31:25 +0000

The list of best practices include: a) Pagination: In this technique, the data retrieved from the server is shown on multiple pages with next and previous buttons. These buttons help in navigating the records. The advantage of using this technique is that the client doesn’t need to wait until all the data is retrieved [...]

What is Chain of Responsibility (CoR) design pattern?

admins — Mon, 21 May 2012 16:29:41 +0000

The basic principle behind CoR is to avoid a component which can perform multiple functions and have a number of components each performing a definitive task. This design pattern is inspired from Cohesion principle which states that each component should perform a unique function. The advantage of using CoR is that a request need not [...]

What is the difference between aggregation and composition?

admins — Mon, 21 May 2012 16:29:02 +0000

Aggregation and composition both refer to a “has a” relationship which means that one object is a part of another object. This relationship is required to model real world scenarios like a school has a principal or a Van has an Engine. The difference between aggregation and composition lies in the kind of “has a” relationship [...]

Explain Factory design pattern

admins — Mon, 21 May 2012 16:27:49 +0000

The Factory design pattern defines a factory which can be used to build objects of particular type. Like a real world factory, the factory class assembles an object using various component or sub objects and the returns the built object. The class which requested the object being build need not take care of creating the [...]

Explain Singleton design pattern?

admins — Mon, 21 May 2012 16:26:22 +0000

Singleton pattern is a solution which comes to help when you want to allow only one instance of a class in your application. Let us understand the concept of singleton pattern using a program. Following is a class which allows only one instance of itself to be created: Example Code: The above solution is thread [...]