Things we will be Discussing:

Array 1D and 2D
Array is a collection of similar type of elements that have contiguous memory location.
Java array is an object the contains elements of similar data type.It is a data structure where we store similar elements. We can store only fixed set of elements in a java array.

Command Line
Command line arguments are stored in the string array which is the parameter of the main method.
public static void main (String args[])
Example - compile.java

Taking Input from User

Java Scanner class allows the user to take input from the console. It belongs to java.util package. It is used to read the input of primitive types like int, double, long, short, float, and byte. It is the easiest way to read input in Java program.

Syntax:

Scanner sc=new Scanner(System.in);

Java Reader Class
Java Reader is an abstract class for reading character streams. The only methods that a subclass must implement are read(char[], int, int) and close(). Most subclasses, however, will override some of the methods to provide higher efficiency, additional functionality, or both.

Buffer Reader Class
Java BufferedReader class is used to read the text from a character-based input stream. It can be used to read data line by line by readLine() method. It makes the performance fast. It inherits Reader class.