Sanjay Bhansali invites you to Freelancer.com

Sanjay Bhansali wants you to join Freelancer.com - the world's largest outsourcing marketplace! I've been using Freelancer.com to hire talented professionals for a fraction of the cost, and to make money by completing work. Accept Invitation

Unsubscribe from this mailing list.

Create android mobile application free

Create android moblie application online free by using following website :

www.appyet.com

I like this site. I sugget all my visiter for this site id u have not knowledge about amdroid programming..

Lexical Issues,Whitespace,Identifiers, Literals,Separators,The Java Keywords

--> Lexical Issues

Java programs are a collection of whitespace,identifiers, comments, literals, operators, separators, and keywords.

Whitespace

Control Statements in java

--> The if Statement

The Java if statement works much like the IF statement in any other language. Further,
it is syntactically identical to the if statements in C, C++, and C#. Its simplest form is
shown here:

if(condition) statement;

Here, condition is a Boolean expression. If condition is true, then the statement is
executed. If condition is false, then the statement is bypassed. Here is an example:

if(num < 100)
println("num is less than 100");

In this case, if num contains a value that is less than 100, the conditional expression
is true, and println( ) will execute. If num contains a value greater than or equal to 100,
then the println( ) method is bypassed.

 Java defines a full complement of relational operators
which may be used in a conditional expression. Here are a few:

Operator          Meaning
<                 Less than
>                 Greater than
==                   Equal to

Notice that the test for equality is the double equal sign.

Here is a program that illustrates the if statement:

/*
Demonstrate the if.
Call this file "IfSample.java".
*/
class IfSample {
public static void main(String args[]) {
int x, y;
x = 10;
y = 20;
if(x &lt; y) System.out.println("x is less than y");
x = x * 2;
if(x == y) System.out.println("x now equal to y");
x = x * 2;
if(x &gt; y) System.out.println("x now greater than y");
// this won't display anything
if(x == y) System.out.println("you won't see this");
}
}
The output generated by this program is shown here:
x is less than y
x now equal to y
x now greater than y

The for Loop


loop statements are an important part of nearly any programming language. Java is no exception. In fact, Java supplies a powerful assortment of loop constructs.
Perhaps the most versatile is the for loop. If you are familiar with C, C++, or C#, then
you will be pleased to know that the for loop in Java works the same way it does in
those languages. If you don’t know C/C++/C#, the for loop is still easy to use. The
simplest form of the for loop is shown here:

for(initialization; condition; iteration) statement;

In its most common form, the initialization portion of the loop sets a loop control
variable to an initial value. The condition is a Boolean expression that tests the loop
control variable. If the outcome of that test is true, the for loop continues to iterate. If it
is false, the loop terminates. The iteration expression determines how the loop control
variable is changed each time the loop iterates. Here is a short program that illustrates
the for loop:

/*
Demonstrate the for loop.
Call this file "ForTest.java".


class ForTest {
public static void main(String args[]) {
int x;
for(x = 0; x<10; x = x+1)
System.out.println("This is x: " + x);
}
}
This program generates the following output:
This is x: 0
This is x: 1
This is x: 2
This is x: 3
This is x: 4
This is x: 5
This is x: 6
This is x: 7
This is x: 8
This is x: 9

In this example, x is the loop control variable. It is initialized to zero in the initialization
portion of the for. At the start of each iteration (including the first one), the conditional
test x < 10 is performed. If the outcome of this test is true, the println( ) statement is
executed, and then the iteration portion of the loop is executed. This process continues
until the conditional test is false.

A First Simple Java Program

Now that the basic object-oriented underpinning of Java has been discussed, let’s
look at some actual Java programs. Let’s start by compiling and running the short
sample program shown here. As you will see, this involves a little more work than
you might imagine.

/*
This is a simple Java program.
Call this file "Example.java".
*/

class Example {
// Your program begins with a call to main().
public static void main(String args[]) {
System.out.println("This is a simple Java program.");
}
}

Entering the Program

 For most computer languages, the name of the file that holds the source code to a program is arbitrary. However, this is not the case with Java. The first thing that you must learn about Java is that the name you give to a source file is very important. For this example, the name of the source file should be Example.java. Let’s see why. In Java, a source file is officially called a compilation unit. It is a text file that contains one or more class definitions. The Java compiler requires that a source file use the .java filename extension. Notice that the file extension is four characters long. As you might guess, your operating system must be capable of supporting long filenames. This means
that DOS and Windows 3.1 are not capable of supporting Java. However, Windows
95/98 and Windows NT/2000/XP work just fine.
As you can see by looking at the program, the name of the class defined by the
program is also Example. This is not a coincidence. In Java, all code must reside inside
a class. By convention, the name of that class should match the name of the file that
holds the program. You should also make sure that the capitalization of the filename
matches the class name. The reason for this is that Java is case-sensitive. At this point,
the convention that filenames correspond to class names may seem arbitrary. However,
this convention makes it easier to maintain and organize your programs.

Compiling the Program
To compile the Example program, execute the compiler, javac, specifying the name of
the source file on the command line, as shown here:

C:\>javac Example.java

The javac compiler creates a file called Example.class that contains the bytecode version
of the program. As discussed earlier, the Java bytecode is the intermediate representation
of your program that contains instructions the Java interpreter will execute. Thus, the
output of javac is not code that can be directly executed.
To actually run the program, you must use the Java interpreter, called java. To do
so, pass the class name Example as a command-line argument, as shown here:

C:\>java Example

When the program is run, the following output is displayed:

This is a simple Java program.

When Java source code is compiled, each individual class is put into its own output
file named after the class and using the .class extension. This is why it is a good idea to
give your Java source files the same name as the class they contain—the name of the
source file will match the name of the .class file. When you execute the Java interpreter
as just shown, you are actually specifying the name of the class that you want the
interpreter to execute. It will automatically search for a file by that name that has
the .class extension. If it finds the file, it will execute the code contained in the
specified class.

Object-Oriented Programming

Object-oriented programming is at the core of Java. In fact, all Java programs are objectoriented—
this isn’t an option the way that it is in C++, for example. OOP is so integral
to Java that you must understand its basic principles before you can write even simple
Java programs. Therefore, this chapter begins with a discussion of the theoretical aspects
of OOP.
Two Paradigms
As you know, all computer programs consist of two elements: code and data. Furthermore,
a program can be conceptually organized around its code or around its data. That is,
some programs are written around “what is happening” and others are written around
“who is being affected.” These are the two paradigms that govern how a program is
constructed. The first way is called the process-oriented model. This approach characterizes
a program as a series of linear steps (that is, code). The process-oriented model can be
thought of as code acting on data. Procedural languages such as C employ this model to
considerable success. However, as mentioned in Chapter 1, problems with this approach
appear as programs grow larger and more complex.
To manage increasing complexity, the second approach, called object-oriented
programming, was conceived. Object-oriented programming organizes a program around
its data (that is, objects) and a set of well-defined interfaces to that data. An object-oriented
program can be characterized as data controlling access to code. As you will see, by switching
the controlling entity to data, you can achieve several organizational benefits.
Abstraction
An essential element of object-oriented programming is abstraction. Humans manage
complexity through abstraction. For example, people do not think of a car as a set of
tens of thousands of individual parts. They think of it as a well-defined object with its
own unique behavior. This abstraction allows people to use a car to drive to the grocery
store without being overwhelmed by the complexity of the parts that form the car. They
can ignore the details of how the engine, transmission, and braking systems work. Instead
they are free to utilize the object as a whole.


A powerful way to manage abstraction is through the use of hierarchical classifications.
This allows you to layer the semantics of complex systems, breaking them into more
manageable pieces. From the outside, the car is a single object. Once inside, you see
that the car consists of several subsystems: steering, brakes, sound system, seat belts,
heating, cellular phone, and so on. In turn, each of these subsystems is made up of more
specialized units. For instance, the sound system consists of a radio, a CD player, and/or
a tape player. The point is that you manage the complexity of the car (or any other
complex system) through the use of hierarchical abstractions.

 The Three OOP Principles
All object-oriented programming languages provide mechanisms that help you implement
the object-oriented model. They are encapsulation, inheritance, and polymorphism.
Let’s take a look at these concepts now.

Encapsulation
Encapsulation is the mechanism that binds together code and the data it manipulates,
and keeps both safe from outside interference and misuse. One way to think about
encapsulation is as a protective wrapper that prevents the code and data from being
arbitrarily accessed by other code defined outside the wrapper. Access to the code
and data inside the wrapper is tightly controlled through a well-defined interface.
To relate this to the real world, consider the automatic transmission on an automobile.
It encapsulates hundreds of bits of information about your engine, such as how much
you are accelerating, the pitch of the surface you are on, and the position of the shift
lever. You, as the user, have only one method of affecting this complex encapsulation:
by moving the gear-shift lever. You can’t affect the transmission by using the turn signal
or windshield wipers, for example. Thus, the gear-shift lever is a well-defined (indeed,
unique) interface to the transmission. Further, what occurs inside the transmission does
not affect objects outside the transmission. For example, shifting gears does not turn
on the headlights! Because an automatic transmission is encapsulated, dozens of car
manufacturers can implement one in any way they please. However, from the driver’s
point of view, they all work the same. This same idea can be applied to programming.
The power of encapsulated code is that everyone knows how to access it and thus
can use it regardless of the implementation details—and without fear of unexpected
side effects.
In Java the basis of encapsulation is the class. Although the class will be examined
in great detail later in this book, the following brief discussion will be helpful now. A
class defines the structure and behavior (data and code) that will be shared by a set of
objects. Each object of a given class contains the structure and behavior defined by the
class, as if it were stamped out by a mold in the shape of the class. For this reason, objects
are sometimes referred to as instances of a class. Thus, a class is a logical construct; an
object has physical reality.
When you create a class, you will specify the code and data that constitute that
class. Collectively, these elements are called members of the class. Specifically, the data
defined by the class are referred to as member variables or instance variables. The code
that operates on that data is referred to as member methods or just methods. (If you are
familiar with C/C++, it may help to know that what a Java programmer calls a method,
a C/C++ programmer calls a function.) In properly written Java programs, the methods
define how the member variables can be used. This means that the behavior and interface
of a class are defined by the methods that operate on its instance data.

Inheritance
Inheritance is the process by which one object acquires the properties of another object.
This is important because it supports the concept of hierarchical classification. As
mentioned earlier, most knowledge is made manageable by hierarchical (that is, top-down)
classifications. For example, a Golden Retriever is part of the classification dog, which
in turn is part of the mammal class, which is under the larger class animal. Without the
use of hierarchies, each object would need to define all of its characteristics explicitly.
However, by use of inheritance, an object need only define those qualities that make it
unique within its class. It can inherit its general attributes from its parent. Thus, it is the
inheritance mechanism that makes it possible for one object to be a specific instance of
a more general case. Let’s take a closer look at this process.

Polymorphism 

Polymorphism (from the Greek, meaning “many forms”) is a feature that allows one interface to be used for a general class of actions. The specific action is determined by the exact nature of the situation. Consider a stack (which is a last-in, first-out list). You might have a program that requires three types of stacks. One stack is used for integer values, one for floating-point values, and one for characters. The algorithm that implements each stack is the same, even though the data being stored differs. In a non– object-oriented language, you would be required to create three different sets of stack routines, with each set using different names. However, because of polymorphism, in Java you can specify a general set of stack routines that all share the same names. More generally, the concept of polymorphism is often expressed by the phrase “one interface, multiple methods.” This means that it is possible to design a generic interface to a group of related activities. This helps reduce complexity by allowing the same interface to be used to specify a general class of action. It is the compiler’s job to select the specific action (that is, method) as it applies to each situation. You, the programmer, do not need to make this selection manually. You need only remember and utilize the general interface.

append( ) in java

The append( ) method concatenates the string representation of any other type of data to the end of the invoking StringBuffer object. It has overloaded versions for all the
built-in types and for Object. Here are a few of its forms:

• StringBuffer append(String str)
• StringBuffer append(int num)
• StringBuffer append(Object obj) 

String.valueOf( ) is called for each parameter to obtain its string representation.
The result is appended to the current StringBuffer object. The buffer itself is returned by each version of append( ). This allows subsequent calls to be chained together, as
shown in the following example:

// Demonstrate append().
 class appendDemo {
public static void main(String args[]) {
 String s; int a = 42;
StringBuffer sb = new StringBuffer(40);
 s = sb.append("a = ").append(a).append("!").toString();
System.out.println(s); }
}

The output of this example is shown here: a = 42!

The append( ) method is most often called when the + operator is used on String objects. Java automatically changes modifications to a String instance into similar operations on a StringBuffer instance. Thus, a concatenation invokes append( ) on a StringBuffer object. After the concatenation has been performed, the compiler inserts a call to toString( ) to turn the modifiable StringBuffer back into a constant String. All of this may seem unreasonably complicated. Why not just have one string class and have it behave more or less like StringBuffer? The answer is performance. There are many optimizations that the Java run time can make knowing that String objects areimmutable. Thankfully, Java hides most of the complexity of conversion between Strings and StringBuffers. Actually, many programmers will never feel the need to
use StringBuffer directly and will be able to express most operations in terms of the
+ operator on String variables.