JAVA - Introduction

 In JAVA, everything is based on classes, sections of code with commands to execute. There are also these things called methods,smaller sections of code that contain functions too.Usually there are multiple methods in a class,that interact with each other based on values of certain variables and return a value. Those methods are packed into a class, and then classes with methods can interact with other classes and print the return value on the screen. There is 
also something called a main method, the method the compiler searches for first. Based on the instructions the main method gives, the compiler can move to different classes to execute different methods,or just stay in the main method.
 For now lets just create a main method. In your "myFirst" class type the code in bold:

public class myFirst {
   
     public static void main(String[] args)
     {
  
     }

}


Now lets discuss this code. Each method is based on the following syntax:

[accessSpecifier] [returnType] [methodName] ( [parameters] )
{
  [methodBody]
}

The access specifiers in this case are "public" and "static". Any method can be "public" or "private". "Public" means the method can be accessed by any class. "Private" means that the method can be accessed by only the class it belongs to. I will explain the "Static" key word later.Here we made a public static main method with the name main, and parameters of "String[] args"(I won't explain the parameters now). In the method body we type all of the commands we wan't to execute. The method body's and class body's are always located between the curly braces.
 NOTE: JAVA is a case sensitive language, so when you type commands, you must type them exactly as specified, or you will get an error!!!!!!

 Now type the code in bold into your main method:


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

}

By now you should have the code in the 1st picture. Now go to "Run" > "Run", and click "OK" when the dialog box appears, and at the bottom(console window) you should see the text "Hello world!" printed. Check the second image for reference.
 Here we used the command System.out.println to print a line on the screen. The "System", is a class containing many functions. The "out" was that we wanted to print OUT to the screen(or output) and the method "println" means; print line. Then in brackets, and in quotation marks(because this is a string value(value containing words)) we included the text we wanted to print,and ended the line with a semi-colon(;). NOTE: All lines in JAVA must end in semi-colons, except lines when we declare classes or methods.
 We can also use "print", but the difference between "print" and "println" is that "print" prints text on a line, but "println" means to print the text, and end the line, meaning that if the next command is "print", the text will be printed on a new line.
 At this point, I would like to apologize for the bad quality of my images.I have included some SELF-CHECK questions at the bottom. In the next step I will include the answers to them.In the next step I will also introduce you to the basic value types.



 SELF-CHECK:

 #1)   Write a program to print the word "cheese" letter by letter.

  HINT: Use the "print" command

#2) Use the "print" and "println" commands to experiment.

#3) What is wrong with this line of code:

     System.out.println(Hello world!);

#4) What will you get if you run these lines of code:

    System.out.print("h");
    System.out.print("i");
    System.out.println("per-");
    System.out.print("son");