First Java Program

 

Let 's create the hello java program:

class  HelloJava
{

public static void main(String args[])

{

System.out.println("Hello Java Java");

}

}

save it by HelloJava.java//you can save it other name but it is good

To Compile: javac  HelloJava.java
To Run: java  HelloJava

Output : Hello Java Java

👉: If you make a java class as a public class, you have to save it as the class name only, you cannot save it to other names than a class name.

For example:

public class  HelloJava

{

public static void main(String args[])

{

System.out.println("Hello Java Java");

}

}

you have to save it by HelloJava.java

To Compile: javac  HelloJava.java

To Run: java  HelloJava

Output : Hello Java Java

Understanding first java program

• class keyword is used to declare a class in java.

• public is an access modifier, it is visible to all. we will learn in later.

• static is a keyword if we declare any method as static, it is known as a static method. it saves a memory.

• void is the return type of the method, it means it doesn't return any value.

• main represents the startup of the program.

• String args[] it is used for command line argument.

• System.out.println() is used print statement in java programs.

Steps to write, compile and run the program in java:

To see clear image, click on image

• To write the program in java open notepad by start menu->All Programs->Accessories->notepad and write a java program.

as displayed in the above diagram, write a java program in notepad and save it as HelloJava.java.

• After writing and saving first java program, To compile and run this program you need to open command prompt go start menu->All Programs->Accessories->command prompt

• To compile and run java program you have to go current directory where you save java file i.e HelloJava.java (we saved this file in C:\java new) and then type javac HelloJava.java for compiling and then enter and then type java HelloJava for running java program.

There are some other ways, we can write a java program .

(1) We can change the sequence of modifiers in the main method.

• static public void main(String args[])

For example:

class Simple
{
static public void main(String args[])
{
System.out.println("hello java");
}
}

output: hello java

(2) We can change subscript notation in java in the main method.

• public static void main(String[] args)

For example:

class Simple

{

public static void main(String[] args)

{

System.out.println("how are you");

}

}

output: how are you

• public static void main(String []args)

For example:

class Simple

{

public static void main(String []args)

{

System.out.println("I am good");

}

}

output: I am good

• public static void main(String args[])

For example:

class Simple

{

public static void main(String args[])

{

System.out.println("Thank you");

}

}

output: Thank you

(3) We can use 3 ellipses(dots) in the main method.

• public static void main(String...s)

For example:

class Simple

{

public static void main(String...s)

{

System.out.println("3 ellipses ...");

}

}

output: 3 ellipses ...

We can apply semicolon (;) at the end of a class in java program. It is optional.

For example:

class Simple

{

public static void main(String []args)

{

System.out.println("we can apply semicolon in java");

}

};

output: we can apply semicolon in java

There are some valid java main method which we can declare

1. public static void main(String[] args)
2. public static void main(String args[])
3. public static void main(String args[])
4. public static void main(String...s)
5. static public void main(String []args)
6. public static final void main(String []args)
7. final public static final void main(String []args)
8. final strictfp public static final void main(String []args)

There are some invalid java main method which we can't declare 

1. static void main(String[] args)
2. public void main(String[] args)
3. public void static main(String[] args)