Java

From AIMSWiki

Java is a modern, object-oriented, compiled computer programming language.

Some resources are here :-

• Java home page (http://www.java.com/en/)
• Sun Java tutorials (http://java.sun.com/docs/books/tutorial/)

Java is 3 things :-

1. A language (syntax, reserved words, etc.)
2. A library (Input / output, many class libraries (http://java.sun.com/javase/6/docs/api/))
3. A virtual machine (the runtime)

Hello world in Java looks like this :-

/**
 * The HelloWorldApp class implements an application that
 * simply prints "Hello World!" to standard output, followed by the numbers 1 to 10.
 */
class HelloWorldApp {
    public static void main(String[] args) {
        System.out.println("Hello World!"); // Display the string.
        for(int i=0; i<10; i++){
                System.out.print(i + " ");
        }
        System.out.println("Finished!");
    }
}

Note the docstring syntax, /**, that is used by other tools to generate documentation.

Java also accepts the C++ style comments, from // to the end of the line.

Then there is the class definition. This is the Java Object - Java is an Object Oriented language.

Like python, filenames in java are tied to objects in the language. This program, with its one class definition, expects to be in a file called HelloWorldApp.java. This class has one method - main. In the Java programming language, every application must contain a main method whose signature is:

public static void main(String[] args)

It is the entry point for the program.

Like C, this program must be compiled before it is run.

javac HelloWorldApp.java      # compile
java HelloWorldApp            # run

Java includes a dissassembler program - javap. It dis-assembles java class files.

Try the following :-

javap HelloWorldApp
javap -c HelloWorldApp