Why String is Immutable in Java ?

String pool (String intern pool) is a special storage area in Java heap. When a string is created and if the string already exists in the pool, the reference of the existing string will be returned, instead of creating a new object and returning its reference.

The following code will create only one string object in the heap.

1.String string1 = “abcd”;
2.String string2 = “abcd”;

If string is not immutable, changing the string with one reference will lead to the wrong value for the other references.

Get previous month’s last date thru javascript

var d = new Date(); // Wed Jan 07 2015
d = new Date(d.getFullYear(),d.getMonth(),0); //Wed Dec 31 2014

adding zero in date column will negative the date by 1day

SAAS vs PAAS vs IAAS

SaaS (Software as a Service) model you are provided with access to application softwares often referred to as on-demand softwares. You don’t have to worry about the installation, setup and running of the application. Service provider will do that for you. You just have to pay and use it through some client. Examples: Google Apps, Microsoft Office 365.

PaaS (Platform as a Service), as the name suggests, provides you computing platforms which typically includes operating system, programming language execution environment, database, web server etc. Examples: AWS Elastic Beanstalk, Windows Azure, Heroku, Force.com, Google App Engine, Apache Stratos.

IaaS (Infrastructure as a Service), as the name suggests, provides you the computing infrastructure, physical or (quite often) virtual machines and other resources like virtual-machine disk image library, block and file-based storage, firewalls, load balancers, IP addresses, virtual local area networks etc. Examples: Amazon EC2, Windows Azure, Rackspace, Google Compute Engine

Hyperlinks

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Enum use in java

Enums are lists of constants. When you need a predefined list of values which do not represent some kind of numeric or textual data, you should use an enum.

http://crunchify.com/why-and-for-what-should-i-use-enum-java-enum-examples/