Java (programming language)

Java is a programming language originally developed by James Gosling at Sun Microsystems(which is now a subsidiary of Oracle Corporation) and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities. Java applications are typically compiledto bytecode (class file) that can run on any Java Virtual Machine (JVM) regardless of computer architecture. Java is a general-purpose, concurrent, class-based, object-oriented language that is specifically designed to have as few implementation dependencies as possible. It is intended to let application developers "write once, run anywhere". Java is currently one of the most popular programming languages in use, and is widely used from application software to web applications.^[9][10]

The original and reference implementation Java compilers, virtual machines, and class librarieswere developed by Sun from 1995. As of May 2007, in compliance with the specifications of theJava Community Process, Sun relicensed most of its Java technologies under the GNU General Public License. Others have also developed alternative implementations of these Sun technologies, such as the GNU Compiler for Java, GNU Classpath, and Dalvik.

James Gosling, Mike Sheridan, and Patrick Naughton initiated the Java language project in June 1991.^[11] Java was originally designed for interactive television, but it was too advanced.^[12] The language was initially called Oak after an oak tree that stood outside Gosling's office; it went by the name Green later, and was later renamed Java, from a list of random words.^[13] Gosling aimed to implement a virtual machine and a language that had a familiar C/C++ style of notation.^[14]

Sun Microsystems released the first public implementation as Java 1.0 in 1995. It promised "Write Once, Run Anywhere" (WORA), providing no-cost run-times on popular platforms. Fairly secure and featuring configurable security, it allowed network- and file-access restrictions. Major web browsers soon incorporated the ability to run Java appletswithin web pages, and Java quickly became popular. With the advent of Java 2 (released initially as J2SE 1.2 in December 1998–1999), new versions had multiple configurations built for different types of platforms. For example,J2EE targeted enterprise applications and the greatly stripped-down version J2ME for mobile applications (Mobile Java).J2SE designated the Standard Edition. In 2006, for marketing purposes, Sun renamed new J2 versions as Java EE, Java ME, and Java SE, respectively.

In 1997, Sun Microsystems approached the ISO/IEC JTC1 standards body and later the Ecma International to formalize Java, but it soon withdrew from the process.^[15] Java remains a de facto standard, controlled through the Java Community Process.^[16] At one time, Sun made most of its Java implementations available without charge, despite their proprietary software status. Sun generated revenue from Java through the selling of licenses for specialized products such as the Java Enterprise System. Sun distinguishes between its Software Development Kit (SDK) and Runtime Environment (JRE) (a subset of the SDK); the primary distinction involves the JRE's lack of the compiler, utility programs, and header files.

On November 13, 2006, Sun released much of Java as open source software under the terms of the GNU General Public License (GPL). On May 8, 2007, Sun finished the process, making all of Java's core code available under free software/open-source distribution terms, aside from a small portion of code to which Sun did not hold the copyright.^[17]

Sun's vice-president Rich Green has said that Sun's ideal role with regards to Java is as an "evangelist."^[18]

Following Oracle Corporation's acquisition of Sun Microsystems in 2009–2010, Oracle has described itself as the "steward of Java technology with a relentless commitment to fostering a community of participation and transparency".^[19]

[edit]Principles

There were five primary goals in the creation of the Java language:^[20]

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"

Performance

Programs written in Java have a reputation for being slower and requiring more memory than those written in C.^[26] However, Java programs' execution speed improved significantly with the introduction of Just-in-time compilation in 1997/1998 for Java 1.1,^[27] the addition of language features supporting better code analysis (such as inner classes, StringBuffer class, optional assertions, etc.), and optimizations in the Java Virtual Machine itself, such as HotSpot becoming the default for Sun's JVM in 2000.

To boost even further the speed performances that can be achieved using the Java language, Systronix made JStik,^[28] a microcontrollerbased on the aJile Systems^[29] line of embedded Java processors. In addition, the widely used ARM family of CPUs has hardware support for executing Java bytecode through its Jazelle option.

A more comprehensive example

// OddEven.java
import javax.swing.JOptionPane;
 
public class OddEven {
    // "input" is the number that the user gives to the computer
    private int input; // a whole number("int" means integer)
 
    /*
     * This is the constructor method. It gets called when an object of the OddEven type
     * is being created.
     */
    public OddEven() {
    /*
     * Code not shown for simplicity.  In most Java programs constructors can initialize objects
     * with default values, or create other objects that this object might use to perform its
     * functions.  In some Java programs, the constructor may simply be an empty function if nothing
     * needs to be initialized prior to the functioning of the object.  In this program's case, an
     * empty constructor would suffice, even if it is empty. A constructor must exist, however if the
     * user doesn't put one in then the compiler will create an empty one.
     */
    }
 
    // This is the main method. It gets called when this class is run through a Java interpreter.
    public static void main(String[] args) {
        /*
         * This line of code creates a new instance of this class called "number" (also known as an
         * Object) and initializes it by calling the constructor.  The next line of code calls
         * the "showDialog()" method, which brings up a prompt to ask you for a number
         */
        OddEven number = new OddEven();
        number.showDialog();
    }
 
    public void showDialog() {
        /*
         * "try" makes sure nothing goes wrong. If something does,
         * the interpreter skips to "catch" to see what it should do.
         */
        try {
            /*
             * The code below brings up a JOptionPane, which is a dialog box
             * The String returned by the "showInputDialog()" method is converted into
             * an integer, making the program treat it as a number instead of a word.
             * After that, this method calls a second method, calculate() that will
             * display either "Even" or "Odd."
             */
            input = Integer.parseInt(JOptionPane.showInputDialog("Please Enter A Number"));
            calculate();
        } catch (NumberFormatException e) {
            /*
             * Getting in the catch block means that there was a problem with the format of
             * the number. Probably some letters were typed in instead of a number.
             */
            System.err.println("ERROR: Invalid input. Please type in a numerical value.");
        }
    }
 
    /*
     * When this gets called, it sends a message to the interpreter.
     * The interpreter usually shows it on the command prompt (For Windows users)
     * or the terminal (For Linux users).(Assuming it's open)
     */
    private void calculate() {
        if (input % 2 == 0) {
            System.out.println("Even");
        } else {
            System.out.println("Odd");
        }
    }
}