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Java Tutorial

Introduction to Java
Hello World Program
Variables and Data types
More about data types
Displaying text using print and println
Displaying text using printf
Java Comments
Naming conventions for Identifiers
Mathematical operations in Java
Taking input from the user

Classes and Objects
Introduction to object oriented programming
The constituents of a Class
Creating objects and calling methods
Get and Set Methods
Default constructor provided by the compiler
Access Specfiers
Scope and lifetime of Variables
Call by value and Call by Reference

A few more topics
Casting
Class as a reference data type
Constants or literals
Final variables
Increment and decrement operators
Manipulating Strings
Operators
Overloading constructors and methods
Static methods and variables
The Java API
The Math class
this keyword
Wrapper classes

Control Structures
Control Statements
Repetition statements
Nested loops
Formulating algorithms
Branching Statements

Arrays
Arrays introduction
Processing arrays using 1oops
Searching and sorting arrays
Array of objects
Multi dimensional arrays
Taking input as command line arguments
Using ellipsis to accept variable number of arguments

Inheritance
Inheritance introduction
Relation between a super class and sub class
Final classes and methods
The protected access specifier
Class Object

Polymorphism
Introduction
Interfaces
Packages
Abstract classes and methods

Exception handling
Exception handling introduction
Exception hierarchy
Nested try catch blocks
Throwing exceptions


Taking Input as Command Line Arguments

You must have now by realised what String[] args within the declaration of the main method means. It represents a String array named args. Since args is nothing more than an identifier, we can replace it with any other identifier and the program will still work. What we need to know now is how a String array can be passed as an argument when we execute the program. We pass it through the command line itself. Consider that we have a class named Add. The following statement normally used to execute the program.

java Add

When we wish to pass the String array, we simply include the elements of the array as simple Strings beside the class name. Enclosing the Strings in quotes is optional. Consecutive Strings are separated with a space. For example, if we wish to pass a three element String array containing the values "1", "2", and "3" any of the following lines is entered on the command prompt.

java Add 1 2 3 
java Add "1" "2" "3"

Since these arguments are passed through the command line, they are known as command line arguments. The String arguments passed are stored in the array specified in the main() declaration. args[] is now a three element String array. These elements are accessed in the same way as the elements of a normal array. The following is the complete Add program which is capable of adding any number of integers passed as command line arguments.

public class Add {

    public static void main(String[] args) {
        int sum = 0;
        for (int i = 0; i < args.length; i++) {
            sum = sum + Integer.parseInt(args[i]);
        }
        System.out.println("The sum of the arguments passed is " + sum);
    }
}

And here are some sample executions from the command line:



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