Java Programing laungage

Core Java Tutorial

Introduction of Core Java

How To Install JDk and Set of Path

Syntax of java Program

Difference between Java and C/C++

Advantage and Disadvantage of Java

What is Java

Why Java is not Pure Object Oriented Language

Java has Following Features/Characteristics

Limitation of Java Language and Java Internet

Common Misconception about Java

Simple Program of Java

Integrated Development Environment in java

Compile and Run Java Program

Applet and Comments in Java

Tokens in Java

Keywords in Java

Identifier and Variables in Java

Literals/Constants

Data Type in Java

Assignments and Initialization in Java

Operators in Java

Rule of Precedence in Java

Operator on Integer and Separators in Java Programming

Java Control Flow of Statements

If and If-else Selection Statement

Nested If-else and If-else-If Selection Statement

switch case and conditional operator Selection Statement

for and while Loop

do..while and for each Loop

break and labeled break statement

continue and labeled continue statement

return Statement and exit() Method

Escape Sequence for Special Characters and Unicode Code

Constants and Block or Scope

Statement in Java

Conversions between Numeric Types in Java

Import Statement in Java

User Input in Java using Scanner Class

User Input in Java using Console Class

Array in Java

One Dimensional Array

Two Dimensional Array

Two Dimensional Array Program

Command Line Argument in Java

String args Types in Java

Uneven/Jagged array in java

Math Class Function and Constant

Math Class all Function used in a program

Enumerated Types in Java

Object Oriented Programming v/s Procedural Programming

Object Oriented Programming Concepts in Java

Introduction to Class,Object and Method in Java

Class Declaration in Java

Class & Objects in java

Encapsulation in Java

Modifiers/Visibility for a Class or Interrface or member of a Class

Polymorphism in Java

Runtime polymorphism (dynamic binding or method overriding)

Class & Objects in java
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Defining a Class

A class represent ADT(Abstract Data Type). it acts like a template using which we can create multiple objects. A class Declaration only create a template, it does not create an actual object. A class creates a new data type that can be used to create object. That is a class creates a logical framework that defines the relationship between its members. when we declare an object of a class, we are creating an instance of that class. Thus a class is a logical construct. An object has physically reality.

Example :

modifiers class <class-name>
{
			modifier type variables;
			.
			.
			.
			.
			modifiers type methodName1(parameter-list)
			{
					<body of the method>
			}
			.
			.
}

 

Declaring Objects

Student s1;

s1 is not an object. In c++ s1 will be treated as object but in java s1 is only a variable which can hold reference to an object of type student. This variable will hold garbage or null reference until we assign reference of some object of class student. It does not yet point to an actual object. Any attempt to use this variable at this point will result in a compile_time error. It is just like a pointer to an object in c/c++. If this variable is declared inside any block or a method then it is a local variable and will not be initialized to null, but if it is declared in a class then it will be an instance variable and will automatically be initialized to null.

Allocating Memory

In java memory is allocated dynamically with the help of new operator.

s1=new student();;

New operator will allocate memory for an object of class student and return its reference, which is then assigned to reference type variable s1. It will also call a default constructor to initialize member variables.

above two statements can be combined:
student s1=new student();

note1:new allocates memory for an object during runtime. If new is unable to allocate memory (because memory is finite.) then it generate a run time exception/error

note2:if we assign a reference variable to another reference variable then only reference (address) will be transferred. There will not be any duplicate copy of the object. for example if we create another reference variable s2(student s2) and then (s1=s2). This will not create duplicate object, same object is referenced by s1 and s2. Any changes made in s2 will also be reflected in s1. No memory allocation is done with this assign. after a few steps if we assign null in s1 then that object will be destroyed by the garbage collector and the memory occupied by that object will be freed.

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