JAVA PROGRAMMING FOR BEGINNERS
Introduction
to Java
Java is defined by a
specification and consists of a programming language, a compiler, core
libraries and a runtime (Java virtual machine) The Java runtime allows software
developers to write program code in other languages than the Java programming language which still runs on the Java virtual machine. The Java platform is
usually associated with the Java virtual machine and
the Java
core libraries.
Properties of
Java
·
Platform
independent
·
Object-orientated
programming language
·
Strongly-typed
programming language
·
Interpreted
and compiled language
·
Automatic
memory management
Java virtual machine
The Java virtual machine (JVM)
is a software implementation of a computer that executes programs like a real
machine.
The
Java virtual machine is written specifically for a specific operating system,
e.g., for Linux a special implementation is required as well as for Windows.
Classes
and Objects
Classes and Objects are basic concepts of Object-Oriented Programming
which revolves around real-life entities.
Classes in Java
The class is a group of similar entities. It is only a logical component and not the physical entity.
A class can contain any of the following variable types.
·
Local
variables −
Variables defined inside methods, constructors or blocks are called local
variables. The variable will be declared and initialized within the method and
the variable will be destroyed when the method has completed.
·
Instance
variables − Instance
variables are variables within a class but outside any method. These variables
are initialized when the class is instantiated. Instance variables can be
accessed from inside any method, constructor or blocks of that particular
class.
·
Class
variables − Class
variables are variables declared within a class, outside any method, with the
static keyword.
object in Java
An object contains both the data and the function,
which operates on the data. An entity that
has state and behavior is known as an object e.g., chair, bike, marker, pen,
table, car, etc. It can be physical or logical (tangible and intangible).
An example of an intangible object is the banking
system. An object has three characteristics:
·
State: represents the data (value) of an object.
·
Behavior: represents the behavior (functionality) of an object such as deposit, withdraw, etc.
·
Identity: An object identity is typically implemented via a
unique ID. The value of the ID is not visible to the external user. However, it
is used internally by the JVM to identify each object uniquely.
Example - chair, bike, marker, pen, table, car, etc.
Difference between object and java
Content of Classes and Object in Java
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