Continued from Lecture 1

Basic program

open Notepad write this program...

class Simple{ public static void main(String args[]) { System.out.println("Hello Java"); } }

save this file as Simple.java

now open command prompt first Setpath as mentioned above now To compile: write javac Simple.java To execute: write java Simple

Output:Hello Java

Let's see what is the meaning of class, public, static, void, main, String[], System.out.println().

1. class keyword is used to declare a class in java.
2. public keyword is an access modifier which represents visibility, it means it is visible to all.
3. static is a keyword, if we declare any method as static, it is known as static method. The core advantage of static method is that there is no need to create object to invoke the static method. The main method is executed by the JVM, so it doesn't require to create object to invoke the main method. So it saves memory.
4. void is the return type of the method, it means it doesn't return any value.
5. main represents startup of the program.
6. String[] args is used for command line argument. We will learn it later.
7. System.out.println() is used print statement. We will learn about the internal working of System.out.println statement later.

What happens at compile time

What happens at Run time

Classloader: is the subsystem of JVM that is used to load class files. Bytecode Verifier: checks the code fragments for illegal code that can violate access right to objects. Interpreter: read bytecode stream then execute the instructions.

What are classes,objects and variable

1. Class is a blue print that has characterstics and behavior
2. Objects have states and behaviors. Example: A dog has states - color, name, breed as well as behaviors -wagging, barking, eating. An object is an instance of a class.
3. Variables are just like a box having certain name containing some value in it

In Next Lecture we will study 1. Detailed study of Classes,Objects and Variables with example

Thank you