[Java] Meaning of Public static void main (String [] args)

public static void main (String [] args) is a required method for running Java. If you make a mistake in even one syntax, an error will occur and you will not be able to execute it. Because each one has its own meaning.

Hello.java

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

The meaning of each item is as follows.

About args

String [] args are values (command line arguments) specified when the program starts. The argument name args is customarily used as args, but you can use another name. The reason why args is used by convention is that Java is the successor to C and inherits the convention of C.

Argument name used in C language

--argv (argument vector (argument array)) --argc (argument count)

Argument operation check

Hello.java

class Hello{
    public static void main(String[] args) {
        System.out.println(args[0]);        
    }
}

• Execution result

$ java Hello "Hello world"
Hello world

--Replace args with sample

Hello.java

class Hello{
    public static void main(String[] sample) {
        System.out.println(sample[0]);        
    }
}

• Execution result

$ java Hello "Hello world"
Hello world

If the syntax is incorrect

If the syntax is incorrect, the execution result will be as follows.

$ java Hello "Hello world"
error:The main method cannot be found in class Hello. Define the main method as follows:
   public static void main(String[] args)

Wrong syntax example

--When the argument is other than a String type array

Hello.java

class Hello{
    public static void main(Integer[] sample) {
        System.out.println(sample[0]);        
    }
}

• The reason why the argument is of type String is that the value received from the command line is a human input character, which is a string *