Every Java program is made up of a collection of objects
that can communicate to each other. Below is a brief description of what the
fundamental parts of a Java program do.
Class – Classes contain Variables
and Methods. Think of a Variable as something that can hold a value. A class is
a blueprint for creating Objects.
Methods – A Method, also known as a
function, is like a behavior. A class can contain lots of Methods. Within each
method logic, which is just code that will be executed when the Method is
called.
Object – An Object is an instance
of a class. When Objects are created they are using the information created
from a particular Class.
Instance Variables – Each object
that is created has a unique set of Instance Variables. These variables come
from the class that the object was instantiated from.
Java Basic Syntax:
When programming it is good to keep naming conventions
universal across all projects. These conventions are good practice and should
be followed at all times, however are not syntactically incorrect if done
differently.
Class Names – The first letter in
all class names should be uppercase. If several words are used for a class
name, each inner words first letter should be uppercase. This is also known as
camel case. (Example: MyAwesomeClass)
Method Names – The first letter in
all method names should be lowercase. If several words are used for the methods
name, each inner word’s first letter should be uppercase. (Example: myAwesomeMethod).
The following naming conventions will cause compile time
errors if incorrect and must be strictly followed.
Case Sensitivity – Java is case
sensitive. This means that example and Example are completely different as far
as Java is concerned.
Program File Names – The name of
the program file should exactly match the Class name. When saving a file, you
should always save it as the class name, followed by the extension (.java).
(Example: If you have a class called ExampleClass, you would save this file as
ExampleClass.java).
Let’s briefly look at how a program knows where to start
running. What happens if our program has 10 different classes? How does it know
where to start?
public static void main(String[] args) – This is a method
that every Java application must implement. There can only ever be one of these
methods inside a Java project, and it is the first method called when you
program is executed. In later tutorials you will have a better understanding of
what exactly each part of that method statement means.
Modifiers:
In Java it is possible to place modifiers on classes,
methods, variables, etc. There are two main types of modifiers.
Access
Modifiers: default, public, protected, private.
Non-access
Modifiers: final, abstract, strictfp.
In the next tutorial we will look into more detail of what
these modifiers mean.
Variables:
Here are some of the main variable types inside of Java.
These variable types are different from data types, these are to do with the
scope (who can access) of the variables.
Local
Variables
Class
Variables (static variables)
Instance
Variables (non-static variables)
Comments
Java allows for single line and multi-line comments, which
are very similar to c++. Any characters that are placed inside a comment are
ignored by the compiler and will not be executed at runtime. Comments are a
good way to explain how parts of your code work and make it more readable.
Below are examples of single and multi-line comments.
