Introduction to Java - Learn Java for Web Development - page 380

Listing A-2. Creating the Object

ClassA var1 = new ClassA();

The process of creating objects involves declaring a reference variable to store the reference value of
the object and then creating the object using the new keyword followed by initializing the object by a
call to a constructor. The concept of constructor is explained later in the appendix. Listing A-3 splits
Listing A-2 to show the declaration and creation as separate steps.

Listing A-3. The Declaration and Creation in Separate Steps

1. ClassA var1 ;
2. var1 = new ClassA();

 var1 . The reference variable var1 can now be
used to manipulate the object whose reference value is stored in the reference
variable.

Line 1 declares the variable

 new keyword and initialization by calling a
constructor ClassA() .

Line 2 creates the object using the

Variables
In Java, variables store values of primitive data types and reference values of objects.

Listing A-4 illustrates variable declarations that can store primitive values.

Listing A-4. Variable Declarations

int a, b, c; // a, b and c are integer variables.
boolean flag; // flag is a boolean variable.
int i = 10, // i is an int variable with initial value 10

Variables that store reference values of objects are called reference variables . The reference variables
specify the type of reference that can be a class, an array, or an interface. Listing A-5 illustrates the
reference variable declaration.

Listing A-5. Reference Variable Declarations

ClassA var1 ; // Variable var1 can reference objects of class ClassA.

The declaration in the listing A-5 does not create any object of class ClassA ; it just creates variable
that can store references of objects of ClassA .

Instance Members
Each object created (as illustrated in Listing A-2) has its own copies of the fields defined in its class.
The fields of an object are called instance variables . The values of the instance variables in an object
make up the object's state. The methods of an object define its behavior. These methods are called