JAVA

JAVA

Java is a general-purpose, concurrent, class-based, object-oriented computer programming languagethat is specifically designed to have as few implementation dependencies as possible. It is intended to let application developers "write once, run anywhere" (WORA), meaning that code that runs on one platform does not need to be recompiled to run on another. Java applications are typically compiled tobytecode (class file) that can run on any Java virtual machine (JVM) regardless of computer architecture. Java is, as of 2012, one of the most popular programming languages in use, particularly for client-server web applications, with a reported 10 million users.Java was originally developed by James Gosling at Sun Microsystems (which has since merged into Oracle Corporation) and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax fromC and C++, but it has fewer low-level facilities than either of them.

Principles

There were five primary goals in the creation of the Java language:

1. It should be "simple, object-oriented and familiar"
2. It should be "robust and secure"
3. It should be "architecture-neutral and portable"
4. It should execute with "high performance"
5. It should be "interpreted, threaded, and dynamic"

Versions

Major release versions of Java, along with their release dates:

• JDK 1.0 (January 21, 1996)
• JDK 1.1 (February 19, 1997)
• J2SE 1.2 (December 8, 1998)
• J2SE 1.3 (May 8, 2000)
• J2SE 1.4 (February 6, 2002)
• J2SE 5.0 (September 30, 2004)
• Java SE 6 (December 11, 2006)
• Java SE 7 (July 28, 2011)

Syntax

The syntax of Java is largely derived from C++. Unlike C++, which combines the syntax for structured, generic, and object-oriented programming, Java was built almost exclusively as an object-oriented language. All code is written inside a class, and everything is an object, with the exception of the primitive data types (e.g. integers, floating-point numbers, boolean values, and characters), which are not classes for performance reasons.

Unlike C++, Java does not support operator overloading or multiple inheritance for classes. This simplifies the language and aids in preventing potential errors and anti-pattern design.

Java uses similar commenting methods to C++. There are three different styles of comments: a single line style marked with two slashes (//), a multiple line style opened with /* and closed with */, and the Javadoc commenting style opened with /** and closed with */. The Javadoc style of commenting allows the user to run the Javadoc executable to compile documentation for the program.

Example:

// This is an example of a single line comment using two slashes
 
/* This is an example of a multiple line comment using the slash and asterisk.
 This type of comment can be used to hold a lot of information or deactivate
 code, but it is very important to remember to close the comment. */
 
/**
 * This is an example of a Javadoc comment; Javadoc can compile documentation
 * from this text.
 */

Hello world

The traditional Hello world program can be written in Java as:

class HelloWorldApp {
    public static void main(String[] args) {
        System.out.println("Hello World!"); // Display the string.
    }
}