Java Basics Syntax

 

When we consider a Java program, it can be defined as a collection of objects that communicate via invoking each other's methods. Let us now briefly look into what do class, object, methods, and instance variables mean.

• Object − Objects have states and behaviors. Example: A dog has states - color, name, breed as well as behavior such as wagging their tail, barking, eating. An object is an instance of a class.

• Class − A class can be defined as a template/blueprint that describes the behavior/state that the object of its type supports.

• Methods − A method is basically a behavior. A class can contain many methods. It is in methods where the logics are written, data is manipulated and all the actions are executed.

• Instance Variables − Each object has its unique set of instance variables. An object's state is created by the values assigned to these instance variables.

First Java Program

public class MyFirstJavaProgram {

   /* This is my first java program.
    * This will print 'Hello World' as the output
    */

   public static void main(String []args) {
      System.out.println("Hello World"); // prints Hello World
   }
}

Let's look at how to save the file, compile, and run the program. Please follow the subsequent steps −
Open notepad and add the code as above.
Save the file as: MyFirstJavaProgram.java.
Open a command prompt window and go to the directory where you saved the class. Assume it's C:\.
Type 'javac MyFirstJavaProgram.java' and press enter to compile your code. If there are no errors in your code, the command prompt will take you to the next line (Assumption : The path variable is set).
Now, type ' java MyFirstJavaProgram ' to run your program.
You will be able to see ' Hello World ' printed on the window.

Output
C:\> javac MyFirstJavaProgram.java
C:\> java MyFirstJavaProgram 
Hello World
Basic Syntax
About Java programs, it is very important to keep in mind the following points.
Case Sensitivity − Java is case sensitive, which means identifier Hello and hello would have different meaning in Java.
Class Names − For all class names the first letter should be in Upper Case. If several words are used to form a name of the class, each inner word's first letter should be in Upper Case.
Example: class MyFirstJavaClass
Method Names − All method names should start with a Lower Case letter. If several words are used to form the name of the method, then each inner word's first letter should be in Upper Case.
Example: public void myMethodName()
Program File Name − Name of the program file should exactly match the class name.