How does the main method work?

问题

I'm the product of some broken teaching and I need some help. I know that there is this thing called the "main method" in Java and I'm sure other programming languages. I know that you need one to make your code run, but how do you use it to make your run? What does it do and what do you need to have it put in it to make your code run?

I know it should look something like this. But almost nothing more.

static void main(String[] args){

}

回答1:

Breaking this down, point-by-point, for the general case:

All Java applications begin processing with a main() method;
Each statement in the main executes in order until the end of main is reached -- this is when your program terminates;
What does static mean? static means that you don't have to instantiate a class to call the method;
String[] args is an array of String objects. If you were to run your program on the command line, you could pass in parameters as arguments. These parameters can then be accessed as you would access elements in an array: args[0]...args[n];
public means that the method can be called by any object.

回答2:

its the entry point for any java program, it does whatever you tell it to do. all you need to do is declare it in one of your source java files and the compiler will find it.

回答3:

Firstly it should be public static void main(String[] args){...}.

It must be public

Take a look at The main method

The JVM will look for this method signature when it runs you class...

java helloWorld.HelloWorld

It represents the entry point for your application. You should put all the required initialization code here that is required to get your application running.

The following is a simple example (which can be executed with the command from above)

package helloWorld;

public class HelloWorldApp {
    public static void main(String[] args) {
        System.out.println("Hello World!"); // Display the string.
    }
}

回答4:

Summary

void means the method returns no value. String[] args represents a string of arguments in an Array type that are passed to the program. main is the single point of entry in to most Java programs.

Extended

Glossing over why it should be public static void... (You wouldn't build a door without a doorknob), methods (equivalent of functions (or subs) in other languages) in Java have a return type. It just so happens that the main method in Java has to return void. In C or C++, the main method can return an int and usually this indicates the code status of the finished program. An int value of 0 is the standard for a successful completion.

To get the same effect in Java, we use System.exit(intValue)

String[] args is a string array of arguments, passed to the main function, usually for specific application use. Usually these are used to modify a default behavior or for flags used in short command line executable applications.

main just means to the JVM, start here! Same name in C and C++ (and probably more).

回答5:

when you execute your class, anything in the main method runs.

回答6:

You should have a main class and a main method. And if you want to find something in the console, you need have one output command at least in the method, like :

System.out.println("Hello World!");

This makes the code running lively.

来源：https://stackoverflow.com/questions/15962535/how-does-the-main-method-work

标签

java

methods

main