Constructors

When you create a new instance (a new object) of a class using the new keyword, a constructor for that class is called. Constructors are used to initialize the instance variables (fields) of an object. Constructors are similar to methods, but with some important differences.

• Constructor name is class name. A constructors must have the same name as the class its in.
• Default constructor. If you don’t define a constructor for a class, a default parameterless constructor is automatically created by the compiler. The default constructor calls the default parent constructor (super()) and initializes all instance variables to default value (zero for numeric types, null for object references, and false for booleans).
• Default constructor is created only if there are no constructors. If you define any constructor for your class, no default constructor is automatically created.
• Differences between methods and constructors.
  • There is no return type given in a constructor signature (header). The value is this object itself so there is no need to indicate a return value.
  • There is no return statement in the body of the constructor.
  • The first line of a constructor must either be a call on another constructor in the same class (using this), or a call on the superclass constructor (using super). If the first line is neither of these, the compiler automatically inserts a call to the parameterless super class constructor.

  These differences in syntax between a constructor and method are sometimes hard to see when looking at the source. It would have been better to have had a keyword to clearly mark constructors as some languages do.

• this(...) – Calls another constructor in same class. Often a constructor with few parameters will call a constructor with more parameters, giving default values for the missing parameters. Use this to call other constructors in the same class.
• super(...). Use super to call a constructor in a parent class. Calling the constructor for the superclass must be the first statement in the body of a constructor. If you are satisfied with the default constructor in the superclass, there is no need to make a call to it because it will be supplied automatically.

AND

A bitwise AND takes two binary representations of equal length and performs the logical AND operation on each pair of corresponding bits. In each pair, the result is 1 if the first bit is 1 AND the second bit is 1. Otherwise, the result is 0. For example:

0101
AND 0011
= 0001


XOR

A bitwise exclusive or takes two bit patterns of equal length and performs the logical XOR operation on each pair of corresponding bits. The result in each position is 1 if the two bits are different, and 0 if they are the same. For example:

0101
XOR 0011
= 0110

In Java, all integer types are signed, and the “<<” and “>>” operators perform arithmetic shifts. Java adds the operator “>>>” to perform logical right shifts, but since the logical and arithmetic left-shift operations are identical, there is no “<<<” operator in Java. These general rules are affected in several ways by the default type promotions; for example, since the eight-bit type byte is promoted to int in shift-expressions,^[2] the expression “b >>> 2” effectively performs an arithmetic shift of the byte value b instead of a logical shift. Such effects can be mitigated by judicious use of casts or bitmasks; for example, “(b & 0xFF) >>> 2” effectively results in a logical shift.

Nowadays, modern web-based application development can’t exist without J2EE-based applications. These applications are built on a highly secure and powerful development platform. There are various Open Source applications that can help J2EE development a great deal. In this article, I would like to share with everyone an easy way to kick off your J2EE learning for almost no cost to you.

Well, to run J2EE compliant web applications, one needs an application server to which one will want to deploy those applications. There are plenty to choose from but I would recommend Apache TomCat 55x which is easy to use and is very reliable. Tomcat is part of Apache’s Jakarta project which is a diverse set of open source Java solutions.

But what tool should you use to, actually, write your code in! There are again a couple good open source IDEs, however the easiest and most robust one is Eclipse. This IDE itself more than just an IDE, it is a development framework which allows developers to use various views and plug-ins to write and debug their code.

To write J2EE compliant web-based applications, MyEclipseIDE.com provides an excellent and inexpensive application which works as plug-in to Eclipse.

That is all. Once you have all these in place, you are set for a good start in J2EE-based web development.