CODEWITHSUNDEEP
java
user3341953
user3341953

Reputation: 319

What is the difference for run or main function in java class

It is my first day to learn java, when we write a class (the very first one). Someone defines a main function someone defines a run function.

Are they the same?

Upvotes: 2

Views: 2875

Answers (5)

Taks
Taks

Reputation: 2083

Lets suppose you have simple java application:

public class SimpleJavaApp {
    public static void main(String[] args) {
        System.out.println("HELLO WORLD");
    }
}

When you compile it from console you type:

javac SimpleJavaApp.java

Next you run it:

java SimpleAppJava

When you run it java will run the "main" method for you. The main method is sort of an start (entry point) for your simple application. The method takes array of string arguments which you can pass to application during execution for instance:

java SimpleJavaApp someArgument

then within application

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

would print you:

someArgument

Next the run method is concept in java concurrency. run method is a start point for every new thread, though you should not worry about these for a while!

Upvotes: 0

Cem Özer
Cem Özer

Reputation: 1283

main method is entry point of a program but run method of Runnable interface is entry point of a thread. JVM looks for a main method, so in order to launch a java program directly from JVM you must have a main method.

Followings do the same job but in different ways.

With just main:

    public class HelloWorld {

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

    }

With calling a thread from main:

    public class HelloThread extends Thread {

        public void run() {
            System.out.println("Hello from a thread!");
        }

        public static void main(String args[]) {
            (new HelloThread()).start();
        }

    }

Examples from docs.oracle

Upvotes: 0

Aniket Kulkarni
Aniket Kulkarni

Reputation: 12993

The main method is similar to the main function in C and C++; it's the entry point for your application and will subsequently invoke all the other methods required by your program.

In the Java programming language, every application must contain a main method whose signature is:

public static void main(String[] args)

The modifiers public and static can be written in either order (public static or static public), but the convention is to use public static as shown above. You can name the argument anything you want, but most programmers choose args or argv.

Someone defines a main function someone defines a run function. Are they the same?

NO. You will learn run() method in Thread chapter. run() is the entry point for the thread execution.

Upvotes: 0

Lajos Arpad
Lajos Arpad

Reputation: 76905

No, they are not the same. Also, in Java there are no functions. Use the term method instead.

If the name of two methods differ, then they are not the same.

Upvotes: 0

VH-NZZ
VH-NZZ

Reputation: 5448

The public static void main(String[] args) method is an optional method that you can implement within your class if you want to execute it as an external Java program. The main static method will be called and an array of String arguments will be passed to it.

For now this no run method to worry about. You will encounter this again at a later stage when learning multi-threading. As said by @PaulDraper in the comments, any other static method that your define in your class can be invoked from main, esp. if you want to keep the latter succinct.

Upvotes: 1

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