Declaring objects

By: aathishankaran Emailed: 1769 times Printed: 2515 times    

Latest comments
By: rohit kumar - how this program is work
By: Kirti - Hi..thx for the hadoop in
By: Spijker - I have altered the code a
By: ali mohammed - why we use the java in ne
By: ali mohammed - why we use the java in ne
By: mizhelle - when I exported the data
By: raul - no output as well, i'm ge
By: Rajesh - thanx very much...
By: Suindu De - Suppose we are executing

Declaring objects

 

            When you create a class, you are creating a new data type. You can use this type to declare objects of that type. However, obtaining objects of a class is a two-step process. First, you must declare a variable of the class type. This variable does not define an object. Instead, it is simply a variable that can refer to an object. Second, you must acquire an actual, physical copy of the object and assign it to that variable. You can do this using the new operator. The new operator dynamically allocates (that is, allocates at run time) memory for an object and returns a reference to it. This reference is, more or less, the address in memory of the object allocated by new. This reference is then stored in the variable. Thus, in java, all class objects must be dynamically allocated. Let’s look at the details of this procedure.

 

            In the preceding sample programs, a line similar to the following is used to declar an object of type Box.

 

     Box mybox = new Box ();

 

            This statement combines the two steps just described. It can be rewritten like this to show each step more clearly;

 

     Box mybox;

     mybox = new Box();

 

This first line declares mybox as a reference to an object of type Box. After this line executes, mybox contains the value the value null, which indicates that it does not yet point to an actual object. Any attempt to use mybox at this point will result in a compile-time error. The next line allocates an actual object and assigns a reference to it to mybox. After the second line executes, you can use mybox as if it were Box object. But in reality, mybox simply holds  the memory address of the actual Box object. The effect of these two lines of code is depicted .


Java Home | All Java Tutorials | Latest Java Tutorials

Sponsored Links

If this tutorial doesn't answer your question, or you have a specific question, just ask an expert here. Post your question to get a direct answer.



Bookmark and Share

Comments(0)


Be the first one to add a comment

Your name (required):


Your email(required, will not be shown to the public):


Your sites URL (optional):


Your comments:



More Tutorials by aathishankaran
Web Security Issues
The Web User's Perspective
Server-side plug-Ins
The best way to avoid security vulnerabilities with new server
JavaScript Security
Window Object
Working with Status Bar Messages
Retrieving a Portion of a String
Referencing Windows
Math Object
Frame Object
Document Object
Closing Windows
Built-in Object in Javascript
Textarea Object

More Tutorials in Java
Update contents of a file within a jar file
Tomcat and httpd configured in port 8080 and 80
Java File
Java String
Count number of vowels, consonants and digits in a String in Java
Reverse a number in Java
Student marks calculation program in Java
Handling Fractions in Java
Calculate gross salary in Java
Calculate average sale of the week in Java
Vector in Java - Sample Program
MultiLevel Inheritance sample in Java
Multiple Inheritance sample in Java
Java program using Method Overriding
Java program to check if user input is an even number

More Latest News
Most Viewed Articles (in Java )
InetAddress Example program in Java
Read from a COM port using Java program
Stack example in Java - push(), pop(), empty(), search()
How to use ArrayList in Java
The Basic Structure of a Simple Java program
Using StringTokenizer in Java
FileReader and FileWriter example program in Java
Transient vs Volatile modifiers in Java
Vector example in Java
Method Overriding in Java
Method Overloading (function overloading) in Java
instanceof sample program in Java
append() in Java
Student marks calculation program in Java
Reading from a file and writing to a file using Java program
Most Emailed Articles (in Java)
Text to Speech conversion program in Java
inheritance in Java
How to initialize an Array and how to copy the array
Using Charts in JasperReports
What is Unicode?
Operator Precedence in Java
Of Object, equals (), == and hashCode ()
DateFormat sample program in Java
A Simple whois program in Java
PushbackReader sample program in Java
CharArrayReader example program in Java
ByteArrayOutputStream - sample program in Java
Vector example in Java
Arrays example in Java - asList(), binarySearch(), fill(), sort(), equals()
HashSet Sample program in Java