Java Public Static Void Main Example

Java :public static void main(String[] args)

The main() method is a special method in Java Programming that serves as the externally exposed entrance point by which a Java program can be run. To compile a Java program, you doesn't really need a main() method in your program. But, while execution JVM ( Java Virtual Machine ) searches for the main() method and starts executing from it.

The main() method must be public, it means that you can call this method from outside of the class you are currently in. Since it's static method , there doesn't need to be an instantiation of the class. It must not return any value, and it must accept a String array as a parameter.

1. The modifiers public and static can be written in either order (static public or public static), but the convention is to use public static as shown above.
2. You can define a main() method with any access modifier or with/without static keyword, but then it is not a valid main() method, as the main method which the JVM uses as an entry-point should be defined as such.
3. You can name the argument anything you want, but most developers choose "args" or "argv".

You can write a program without defining a main() it gets compiled without compilation errors . But when you execute it, a run time error is generated saying "Main method not found".

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Let's split it and understand one by one.

public

It is an access specifier that means main() method is accessible globally available . This is necessary because this method is being called by the Java Runtime Environment (JRE) which is not located in your current class. It is important to note that if you make main() method non-public then it's not allowed to be executed by any program, there are some access restrictions applied.

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static

The main() method in Java must be static, because they can then be invoked by the runtime engine without having to instantiate any objects then the code in the body of main() method will do the rest. The main() method should be static because otherwise there would be ambiguity : which constructor should be called? If the main() is allowed to be non-static, then while calling the main() method JVM has to instantiate its class. While instantiating it has to call the constructor of that class, There will be ambiguity if the constructor of that class takes an argument.

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void

Java is a platform independent programming language and if it will return some value then the value may mean different things to different platforms. The "void" is a return type i.e it does not return any value. When the main() method terminates, the java program terminates too. Hence, it doesn't make any sense to return from main() method. If the main() method spawns new threads, then these threads can keep program running. The return type of main doesn't make much sense at this point. If you try to return something from the main method, it will give compilation error as an unexpected return value.

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main()

It's just the name of method or a function name. This name is fixed and as it's called by the JVM as entry point for an application. It's not a keyword.

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String args[]

These are the arguments of type String that your Java application accepts when you run it. Java main() method accepts only string type of argument and stores it in a string array. It is a collection of Strings , separated by a space, which can be typed into the program on the terminal.

As the Java language allows the brackets [] to be positioned after the type or the variable (the first is generally preferred)

If you wanted to output the contents of args , you can just loop through them like this...

Run the java program with arguments like the following:

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Source: http://net-informations.com/java/basics/main.htm

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