Tutorial

public static void main(String[] args) - Java main method

Updated on November 5, 2022

Java

public static void main(String[] args) - Java main method

Introduction

The Java main method is usually the first method you learn about when you start programming in Java because its the entry point for executing a Java program. The main method can contain code to execute or call other methods, and it can be placed in any class that’s part of a program. More complex programs usually have a class that contains only the main method. The class that contains the main method can have any name, although typically you can just call the class Main.

In the examples that follow, the class that contains the main method is called Test:

Test.java

public class Test {

	public static void main(String[] args){

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

In this article you’ll learn what each component of the main method means.

Java Main Method Syntax

The syntax of the main method is always:

public static void main(String[] args){
	// some code
}

You can change only the name of the String array argument. For example, you can change args to myStringArgs. The String array argument can be written as String... args or String args[].

`public`

The access modifier of the main method needs to be public so that the JRE can access and execute this method. If a method isn’t public, then access is restricted. In the following example code, the main method is missing the public access modifier:

Test.java

public class Test {

	static void main(String[] args){

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

When you compile and run the program, the following error occurs because the main method isn’t public and the JRE can’t find it:

javac Test.java 
java Test

OutputError: Main method not found in class Test, please define the `main` method as:
   public static void main(String[] args)
or a JavaFX application class must extend javafx.application.Application

`static`

When the Java program starts, there is no object of the class present. The main method has to be static so that the JVM can load the class into memory and call the main method without creating an instance of the class first. In the following example code, the main method is missing the static modifier:

Test.java

public class Test {

	public void main(String[] args){

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

When you compile and run the program, the following error occurs because the main method isn’t static:

javac Test.java 
java Test

OutputError: Main method is not static in class Test, please define the `main` method as:
   public static void main(String[] args)

`void`

Every Java method must provide the return type. The Java main method return type is void because it doesn’t return anything. When the main method is finished executing, the Java program terminates, so there is no need for a returned object. In the following example code, the main method attempts to return something when the return type is void:

Test.java

public class Test {

	public static void main(String[] args){
	
		return 0;
	}
}

When you compile the program, the following error occurs because Java doesn’t expect a return value when the return type is void:

javac Test.java

OutputTest.java:5: error: incompatible types: unexpected return value
	return 0;
	       ^
1 error

`main`

The Java main method is always named main. When a Java program starts, it always looks for the main method. The following example code shows a main method renamed to myMain:

Test.java

public class Test {

	public static void myMain(String[] args){

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

When you compile and run the program, the following error occurs because the JRE can’t find the main method in the class:

javac Test.java 
java Test

OutputError: Main method not found in class Test, please define the `main` method as:
   public static void main(String[] args)
or a JavaFX application class must extend javafx.application.Application

`String[] args`

Java main method accepts a single argument of type String array. Each string in the array is a command line argument. You can use command line arguments to affect the operation of the program, or to pass information to the program, at runtime. The following example code shows how to print the command line arguments that you enter when you run the program:

Test.java

public class Test {

	public static void main(String[] args){

    	for(String s : args){
		System.out.println(s);
    	}
	
    }
}

When you compile the program and then run it with a few command line arguments separated by spaces, the arguments get printed in the terminal:

javac Test.java 
java Test 1 2 3 "Testing the main method"

Output1
2
3
Testing the main method

Conclusion

In this article you learned about each component of the Java main method. Continue your learning with more Java tutorials.

Thanks for learning with the DigitalOcean Community. Check out our offerings for compute, storage, networking, and managed databases.

Learn more about our products

About the author(s)

See author profile

Category:

Tutorial

Tags:

Java

Still looking for an answer?

Ask a question Search for more help

Was this helpful?

Tutorial

public static void main(String[] args) - Java main method

About the author(s)

Still looking for an answer?

Try DigitalOcean for free

Popular Topics

Congratulations on unlocking the whale ambience easter egg!

Become a contributor for community

DigitalOcean Documentation

Resources for startups and SMBs

Get our newsletter

The developer cloud

Get started for free

Community

Product Docs

Marketplace

DigitalOcean Blog