Core Java : Lecture 2

Continued from Lecture 1Basic programopen Notepad write this program…class Simple{
public static void main(String args[])
System.out.println(“Hello Java”);
}save this file as Simple.javanow open command prompt first Setpath as mentioned above now To compile: write javac To execute: write java SimpleOutput:Hello JavaLet’s see what is the meaning of class, public, static, void, main, String[], System.out.println().class keyword is used to declare a class in java.public keyword is an access modifier which represents visibility, it means it is visible to all.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.void is the return type of the method, it means it doesn’t return any value.main represents startup of the program.String[] args is used for command line argument. We will learn it later.System.out.println() is used print statement. We will learn about the internal working of System.out.println statement later.What happens at compile timeWhat happens at Run timeClassloader: 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 variableClass is a blue print that has characterstics and behaviorObjects 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.Variables are just like a box having certain name containing some value in itIn Next Lecture we will study
1. Detailed study of Classes,Objects and Variables with exampleThank you

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