Creating Object Instances v11

To create an instance of an object type, you must first declare a variable of the object type, and then initialize the declared object variable. The syntax for declaring an object variable is:

<object> <obj_type>

object is an identifier assigned to the object variable.

obj_type is the identifier of a previously defined object type.

After declaring the object variable, you must invoke a constructor method to initialize the object with values. Use the following syntax to invoke the constructor method:

[NEW] <obj_type> ({<expr1> | NULL} [, {<expr2> | NULL} ] [, ...])

obj_type is the identifier of the object type’s constructor method; the constructor method has the same name as the previously declared object type.

expr1, expr2, … are expressions that are type-compatible with the first attribute of the object type, the second attribute of the object type, etc. If an attribute is of an object type, then the corresponding expression can be NULL, an object initialization expression, or any expression that returns that object type.

The following anonymous block declares and initializes a variable:

DECLARE
    v_emp           EMP_OBJ_TYP;
BEGIN
    v_emp := emp_obj_typ (9001,'JONES',
        addr_obj_typ('123 MAIN STREET','EDISON','NJ',08817));
END;

The variable (v_emp) is declared with a previously defined object type named EMP_OBJ_TYPE. The body of the block initializes the variable using the emp_obj_typ and addr_obj_type constructors.

You can include the NEW keyword when creating a new instance of an object in the body of a block. The NEW keyword invokes the object constructor whose signature matches the arguments provided.

The following example declares two variables, named mgr and emp. The variables are both of EMP_OBJ_TYPE. The mgr object is initialized in the declaration, while the emp object is initialized to NULL in the declaration, and assigned a value in the body.

DECLARE
    mgr  EMP_OBJ_TYPE := (9002,'SMITH');
    emp  EMP_OBJ_TYPE;
BEGIN
    emp := NEW EMP_OBJ_TYPE (9003,'RAY');
END;

[ ROW ] ({ <expr1> | NULL } [, { <expr2> | NULL } ] [, ...])

ROW is an optional keyword if two or more terms are specified within the parenthesis-enclosed, comma-delimited list. If only one term is specified, then specification of the ROW keyword is mandatory.