Explain Declaration Of Objects In Java, How To Declare The Object In Java Explain With Example
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Declaration Of Objects In Java
As just explained, 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 declare 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; // declare reference to object
mybox = new Box(); // allocate a Box object
The first line declares
mybox
as a reference to an object of type
Box
. After this line executes,
mybox
contains 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
.