Lets re-look at the
Java Sample Program - Simple Hello World Program In Java which was discussed long time back. Now that we understand classes, methods and there return types, static methods, arrays and access specifiers, lets see how the simple java program which was very confusing then, will be very clear now.
class PrintHelloWorld
{
public static void main(String args[])
{
System.out.println("Hello World");
}
}
- Why
class
: In Java, every line of code/statement should be included as part of a class, that is the reason, we have defined a class
with the name of the program PrintHelloWorld
.
- Why
main
: When we run the program using java PrintHelloWorld
it will look for the method main
in the class PrintHelloWorld
. The method main
is the starting point of execution of the program.
- Why
static
: If we want to call a method, we should have an object, since we can not create an object without going into main method, it will become a problem. If we make the main
method as static
then we can call it with out creating any object.
- Why
public
: Since the main
method should be accessible from outside of the program and probably from different packages, you need to make it public
. If you make it private
or protected
or default
, then the method can not be accessed from a different package.
- Why
void
: Even if return any parameter from the main
method, the program does not know what to do with it. If you want to return a process exit code, we should use the method System.exit
and the not return the value from main
method.
- Why
String[]
: One way to pass parameters to java program, is to use the command line arguments. When we run the program with command line arguments, the arguments are converted into a String
array and passed as a parameter to the main
method.