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Creating Your First Java Classes
Chapter 1
COBOL (COmmon Business Oriented Language)
FORTRAN (FORmula TRANslation)
BASIC (Beginner All-purpose Symbolic Instructional Code)
Pascal (structured programming)
Ada (multi purpose language)
C (whose developer designed B first)
Visual Basic (Basic-like visual language developed by
Microsoft)
Delphi (Pascal-like visual language developed by Borland)
C++ (an object-oriented language, based on C)
C# (a Java-like language developed by Microsoft)
Java
2
Created by Sun Microsystems team led by James
Gosling (1991)
Originally designed for programming home
appliances
Difficult task because appliances are controlled by a
wide variety of computer processors
Team developed a two-step translation process to
simplify the task of compiler writing for each class of
appliances
Initially called “Oak” programs
Unfortunately, the concept was much too advanced
for appliance technology at the time
Fortunately, it was just right for the Internet,
which was just starting to take off
In 1995, the team announced that the Netscape
Navigator Internet browser would incorporate Java
technology
Today, Java not only permeates the Internet, but
also is the invisible force behind many of the
applications and devices that power our day-today lives.
mobile phones
handheld devices
games
navigation systems
e-business solutions
Java is everywhere!
Java Is Simple
Java is partially modeled on C++, but greatly
simplified and improved. Some people refer
to Java as "C++--" because it is like C++ but
with more functionality and fewer negative
aspects.
Java Is Simple
Java Is Object-Oriented
Java is inherently object-oriented.
Although many object-oriented
languages began strictly as procedural
languages, Java was designed from the
start to be object-oriented. Objectoriented programming (OOP) is a
popular programming approach that is
replacing traditional procedural
programming techniques.
One of the central issues in software
development is how to reuse code.
Object-oriented programming provides
great flexibility, modularity, clarity, and
reusability through encapsulation,
inheritance, and polymorphism.
Java Is Simple
Java Is Object-Oriented
Java Is Distributed
Distributed computing involves several
computers working together on a
network. Java is designed to make
distributed computing easy. Since
networking capability is inherently
integrated into Java, writing network
programs is like sending and receiving
data to and from a file.
Java Is Simple
Java Is Object-Oriented
Java Is Distributed
Java Is Interpreted
You need an interpreter to run Java
programs. The programs are compiled
into the Java Virtual Machine code called
bytecode. The bytecode is machineindependent and can run on any
machine that has a Java interpreter,
which is part of the Java Virtual Machine
(JVM).
Java Is Simple
Java Is Object-Oriented
Java Is Distributed
Java Is Interpreted
Java Is Robust
Java compilers can detect many
problems that would first show up at
execution time in other languages.
Java has eliminated certain types of
error-prone programming constructs
found in other languages.
Java has a runtime exception-handling
feature to provide programming
support for robustness.
Java Is Simple
Java Is Object-Oriented
Java Is Distributed
Java Is Interpreted
Java Is Robust
Java Is Secure
Java implements several security
mechanisms to protect your system
against harm caused by stray programs.
Java Is Simple
Java Is Object-Oriented
Java Is Distributed
Java Is Interpreted
Java Is Robust
Java Is Secure
Java Is ArchitectureNeutral
Write once, run anywhere
With a Java Virtual Machine (JVM),
you can write one program that will
run on any platform.
Java Is Simple
Java Is Object-Oriented
Java Is Distributed
Java Is Interpreted
Java Is Robust
Java Is Secure
Java Is ArchitectureNeutral
Java Is Portable
Because Java is architecture neutral,
Java programs are portable. They can
be run on any platform without being
recompiled.
Java Is Simple
Java Is Object-Oriented
Java Is Distributed
Java Is Interpreted
Java Is Robust
Java Is Secure
Java Is ArchitectureNeutral
Java Is Portable
Java's Performance
Java’s performance Because Java is
architecture neutral, Java programs are
portable. They can be run on any
platform without being recompiled.
Java Is Simple
Java Is Object-Oriented
Java Is Distributed
Java Is Interpreted
Java Is Robust
Java Is Secure
Java Is ArchitectureNeutral
Java Is Portable
Java's Performance
Java Is Multithreaded
Multithread programming is smoothly
integrated in Java, whereas in other
languages you have to call procedures
specific to the operating system to enable
multithreading.
Java Is Simple
Java Is Object-Oriented
Java Is Distributed
Java Is Interpreted
Java Is Robust
Java Is Secure
Java Is ArchitectureNeutral
Java Is Portable
Java's Performance
Java Is Multithreaded
Java Is Dynamic
Java was designed to adapt to an evolving
environment. New code can be loaded on
the fly without recompilation. There is no
need for developers to create, and for
users to install, major new software
versions. New features can be
incorporated transparently as needed.
Java is an object-oriented programming
(OOP) language
Programming methodology that views a
program as consisting of objects that interact
with one another by means of actions (called
methods)
Objects of the same kind are said to have the
same type or be in the same class
Most high-level languages have constructs
called procedures, methods, functions,
and/or subprograms
These types of constructs are called methods in
Java
All programming constructs in Java, including
methods, are part of a class
High-level language: A language that people can read,
write, and understand
A program written in a high-level language must be translated into
a language that can be understood by a computer before it can be
run
Machine language: A language that a computer can
understand
Low-level language: Machine language or any language
similar to machine language
Compiler: A program that translates a high-level language
program into an equivalent low-level language program
This translation process is called compiling
The compilers for most programming languages
translate high-level programs directly into the
machine language for a particular computer
Since different computers have different machine
languages, a different compiler is needed for each one
In contrast, the Java compiler translates Java
programs into byte-code, a machine language for a
fictitious computer called the Java Virtual Machine
Once compiled to byte-code, a Java program can be used
on any computer, making it very portable
When you create and save the Java code for an
application, the code is saved as a java file
Filename . java
When the java file is compiled, it creates a class file
which can run the application
Filename . class
There are three
primary components
of a Java program
Class {
Main {
Class
Main method
Java code
code goes here
}
}
One of the first Java classes written to
welcome Java to the internet (Hello World)
class HelloWorld {
public static void main(String[ ] args) {
System.out.println("Hello World!");
}
}
Let’s examine
the code line by
line:
class HelloWorld
This line declares a new class, called "HelloWorld”. A class is composed of
data variables (members), and functions (methods).
public static void main(String args[ ])
class HelloWorld {
public static void main(String[ ] args) {
System.out.println("Hello World!");
}
}
All applications written in Java share at least one thing in common - they all
have a main method. You must declare a public static main method that
accepts command line parameters (args), for your application to run.
System.out.println ("Hello world!");
This is where our application writes a message to the user. System.out is an
object that allows us to write to "standard output", which is the user's
console.
Copy this code to create a box
import javax.swing.*;
public class HelloWorldBox{
public static void main(String[ ] args){
JFrame frame = new JFrame("HelloWorldBox");
final JLabel label = new JLabel("Hello World!");
frame.getContentPane( ).add(label);
frame.setSize(200, 100);
frame.setVisible(true);
}
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
Steps involved in developing a Java program
