Java Reference
In-Depth Information
Let's take a look at some examples that declare and initialize reference types. Suppose
we declare a reference of type
java.util.Date
and a reference of type
String
:
java.util.Date today;
String greeting;
The
today
variable is a reference of type
Date
and can only point to a
Date
object. The
greeting
variable is a reference that can only point to a
String
object. A value is assigned
to a reference in one of two ways:
A reference can be assigned to another reference of the same type.
A reference can be assigned to a new object using the
new
keyword.
For example, the following statements assign these references to new objects:
today = new java.util.Date();
greeting = “How are you?”;
The
today
reference now points to a new
Date
object in memory, and
today
can be
used to access the various fi elds and methods of this
Date
object. Similarly, the
greeting
reference points to a new
String
object,
“How are you?”
The
String
and
Date
objects
do not have names and can only be accessed via their corresponding reference. Figure 1.6
shows how the reference types appear in memory.
FIGURE 1.6
An object in memory can only be accessed via a reference.
A Date object
A Date reference
today
day
29
month
7
year
2011
A String reference
greeting
A String object
How are you?
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