A class is a template for objects with identical structure, and has the form:
ClassName(Parameters): SuperClass
Declarations
StatementsA class has a name as specified by ClassName.
A class may have parameters as specified by Parameters – if no parameters, the brackets are not needed. The Parameters may be one or more declarations of data-items or virtual methods and classes. Virtual methods and classes as parameters are explained in chapter .
A class may have a superclass as specified by SuperClass. We explain superclass in chapter .
The body of a class consists of a sequence of possible declarations and statements as specified by Declarations and Statements.
Class instantiation
We have seen two ways of creating objects from a class as shown here:
JohnSmithsAccount: obj Account(JohnSmithsProfile)
anAccount: ref Account
anAccount := Account(LindaBerrysProfile)We have explained the difference between using obj and ref in sections and .
The declaration:
JohnSmithsAccount: obj Account(JohnSmithsProfile),
and the statement:
anAccount := Account(LindaBerrysProfile)
both include an expression Account(...). This expression creates an Account-object with actual parameters (...) – either JohnSmithsProfile or LindaBerrysProfile.
The evaluation of the expression returns a reference to the newly created Account-object. In JohnSmithsAccount: obj Account(JohnSmithsProfile), JohnSmithsAccount is holding this reference.
In the statement anAccount := Account(LindaBerrysProfile), this reference is assigned to anAccount.
Execution of the expression Account(...) also implies that first the declarations in Account are generated and second the statements in Account are executed. Note that even if declarations and statements may be mixed, the declarations are allocated before the statements are executed.
The object X executing Account(...) is called the invoker and the Account-object being generated is called the callee.
Instantiation of a singular object takes place in the same way as instantiation of a class, except that there are no actual parameters.
