[TUT] Basic syntax of Java programming language - PART 1

[CodingSource]

To start, Java is a high-level programming language developed by Sun Microsystems and released in 1995. Java runs on different kinds of operating systems, such as Windows, Mac OS, and different kinds of versions of UNIX. This tutorial gives a complete understanding of Java's basic syntax.

A Java program can be defined as a collection of objects that communicate by invoking each other's methods. Let us now take a close look into what do class, object, methods and instance in the following mean.

- Object: Objects have states and behaviors. For example, we know that a dog has the following states: color, name, and breed. It also have behaviors too, such a wagging, barking, and eating. An object is an instance of a class.

- Class: A class is like a template or blue print that describes the behaviors or states of that object of its type support. A class can contain methods. What is a method anyway?

- Methods: A method is a behavior. It is in methods where the logics are written, data is manipulated and all the actions are executed.

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


HELLO WORLD PROGRAM
1. Open notepad and type the following code:

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
    }
}

2. Ctrl + S and save the file as "HelloWorld.java".
3. Run CMD and type the directory where you saved the file.
4. Type ' javac HelloWorld.java ' and press enter to compile your code. If there are no errors in your code (and of course it doesn't have, for now), the command prompt will take you to the next line. Let's assume that the path variable is set.
5. Now, type ' java HelloWorld ' to run your program, you should see that "Hello World" is printed on the window.

The CMD's screen should be the following:

C : > javac MyFirstJavaProgram.java
C : > java MyFirstJavaProgram 
Hello World

BASIC SYNTAX:

About Java programs, it is very important to remember the following pointers:
- Case Sensitivity: The programming language is case sensitive. For example, the identifier "Hello" and "hello" means two different things in Java.
- Class Names: For all class names the first letter should be capital. If several words are used to form a name of the class, each inner word's first letter should be in Upper Case. For 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. For example, public void myMethodName()
- Program File Name: Name of the program file should exactly match the class name. When saving the file, you should save it using the class name (Remember Java is case sensitive) and append '.java' to the end of the name (if the file name and the class name do not match your program will not compile). Example : Assume 'MyFirstJavaProgram' is the class name. Then the file should be saved as 'MyFirstJavaProgram.java'
- public static void main(String args[]): Java program processing starts from the main() method which is a mandatory part of every Java program..

Java Identifiers:
All Java components require names. Names used for classes, variables and methods are called identifiers.

In Java, there are several points to remember about identifiers. They are as follows:

- All identifiers should begin with a letter (A to Z or a to z), currency character ($) or an underscore (_).

- After the first character identifiers can have any combination of characters.

- A key word cannot be used as an identifier.

- Most importantly identifiers are case sensitive.

- Examples of legal identifiers: age, $salary, _value, __1_value

- Examples of illegal identifiers: 123abc, -salary

Java Modifiers:
Like other languages, it is possible to modify classes, methods, etc., by using modifiers. There are two categories of modifiers:

- Access Modifiers: default, public , protected, private

- Non-access Modifiers: final, abstract, strictfp

Java Variables:
We would see following type of variables in Java:

- Local Variables
- Class Variables (Static Variables)
- Instance Variables (Non-static variables)
- Java Arrays:
- Arrays are objects that store multiple variables of the same type. However, an array itself is an object on the heap. We will look into how to declare, construct and initialize in the upcoming chapters.

Java Enums:
Enums were introduced in java 5.0. Enums restrict a variable to have one of only a few predefined values. The values in this enumerated list are called enums.

With the use of enums it is possible to reduce the number of bugs in your code.

For example, if we consider an application for a fresh juice shop, it would be possible to restrict the glass size to small, medium and large. This would make sure that it would not allow anyone to order any size other than the small, medium or large.

class FreshJuice {

   enum FreshJuiceSize{ SMALL, MEDIUM, LARGE }
   FreshJuiceSize size;
}

public class FreshJuiceTest {

   public static void main(String args[]){
      FreshJuice juice = new FreshJuice();
      juice.size = FreshJuice. FreshJuiceSize.MEDIUM ;
      System.out.println("Size: " + juice.size);
   }
}

Above example will produce the following result:

Size: MEDIUM

Note: enums can be declared as their own or inside a class. Methods, variables, constructors can be defined inside enums as well.


In the next part we will be talking about keywords, comments, using blank lines, inheritance, and interfaces.

 

[line1]

pa sub po ako ts!, gusto ko po matuto basic nito.thanks