Table of contents
Structure of Java File
Source code that we write will be saved using extension .java
Every thing written in .java file must be in classes, or we can say that every file having .java extension is a class
A class with same name as file name must be present in .java file
First alphabet of class name can be in upper case. It is the naming convention of class name. However, it is not compulsory to do so.
Class which is having same name as file must be public class
A main function/method must be present in this public class, main is a function from where the program starts.
What is package ?
- It is just a folder in which java files lies.
- It is used to provide some rules and stuff to our programs.
Hello world program
public class Main{
public static void main(String [] args){
System.out.println("Hello World");
}
}
public (in first line):- public is an access modifier which allows accessing the class from anywhere.
class :- It is a name group of properties and functions
Main :- It is just the name of class as same as the name of file.
public (in second line) :- It is used to allow the program to use main function from anywhere.
static :- It is a keyword which helps the main method to run without using objects.
void :- It is a keyword used when we do not want to return anything from a method/function.
main :-It is the name of method.
String [] args :- It is a command line argument of string type array.
System :- It is a final class defined in java.lang package.
out :- It is a variable of PrintStream type which is public and static member field of the System class.
println :- It is a method of PrintStream class, It prints the arguments passed to it and adds a new line.
Note :- print can also be used here, but it prints only arguments passed to it. It does not add a new line.