Creates an instance of a class (object) using
the NEW function and assigns its object reference to an appropriately
defined ABL data element. Once assigned, you can use the object
reference to access this class instance and its PUBLIC data members,
properties, and methods. For more information on object references,
see the reference entry for a Class-based object reference:
Syntax
object-reference = new-function [ NO-ERROR ]
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object-reference
- The name of an ABL data element to which you want to assign
the object reference of a new instance of the class specified by new-function.
This data element must be defined as a compatible class or interface
type and can be one of the following:
To be compatible, the object type of object-reference must
be:
- The same class type as the class instantiated by new-function
- A super class of the class instantiated by new-function
- An interface that is implemented by the class instantiated by new-function
-
new-function
- An invocation of the NEW function, which creates an instance
of a specified class and returns an object reference to that instance.
This is the syntax for the NEW function, where object-type-name must
specify a class type consistent with the object type of object-reference:
The value of new-function is restricted to alphanumeric characters
plus the symbols #, $, %, and _.
NEW object-type-name ( [ parameter[ , parameter ]...] )
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The parameter list specifies
the class constructor that is used to instantiate the class. For
more information on the syntax and operation of the NEW function,
see the NEW function (classes) reference entry.
- NO-ERROR
- Suppresses ABL errors or error messages that would otherwise occur and diverts them to
the ERROR-STATUS system handle. If an error
occurs, the action of the statement is not done and execution continues with the next
statement. If the statement fails, any persistent side-effects of the statement are
backed out. If the statement includes an expression that contains other executable
elements, like methods, the work performed by these elements may or may not be done,
depending on the order the AVM resolves the expression elements and the occurrence of
the error.
For the NEW statement, after the statement completes,
object-reference remains unchanged. If a RETURN statement or an UNDO statement with the THROW or RETURN ERROR
options in a constructor raises ERROR and also returns an error string, you can obtain
this string value after the assignment statement completes using the RETURN-VALUE function.
To check for
errors after a statement that uses the NO-ERROR option:
- Check the ERROR-STATUS:ERROR attribute to see if the AVM raised the ERROR
condition.
- Check if the ERROR-STATUS:NUM-MESSAGES attribute is greater than zero to see if
the AVM generated error messages. ABL handle methods used in a block without
a CATCH end block treat errors as warnings and do not raise ERROR, do not set the
ERROR-STATUS:ERROR attribute, but do add messages to the ERROR-STATUS system handle.
Therefore, this test is the better test for code using handle methods without CATCH
end blocks. ABL handle methods used in a block with a CATCH end block raise
ERROR and add messages to the error object generated by the AVM. In this case, the
AVM does not update the ERROR-STATUS system handle.
- Use ERROR-STATUS:GET-MESSAGE( message-num ) to retrieve a
particular message, where message-num is 1 for the first
message.
If the statement does not include the NO-ERROR option, you can use a CATCH end
block to handle errors raised by the statement.
Some other important usage notes
on the NO-ERROR option:
- NO-ERROR does not suppress errors that raise the STOP or QUIT condition.
- A CATCH statement, which introduces a CATCH end block, is analogous to a NO-ERROR
option in that it also suppresses errors, but it does so for an entire block of
code. It is different in that the error messages are contained in a class-based
error object (generated by the AVM or explicitly thrown), as opposed to the
ERROR-STATUS system handle. Also, if errors raised in the block are not handled by a
compatible CATCH block, ON ERROR phrase, or UNDO statement, then the error is not
suppressed, but handled with the default error processing for that block type.
- When a statement contains the NO-ERROR option and resides in a block with a CATCH
end block, the NO-ERROR option takes precedence over the CATCH block. That is, an
error raised on the statement with the NO-ERROR option will not be handled by a
compatible CATCH end block. The error is redirected to the ERROR-STATUS system
handle as normal.
- If an error object is thrown to a statement that includes the NO-ERROR option,
then the information and messages in the error object will be used to set the
ERROR-STATUS system handle. This interoperability feature is important for those
integrating code that uses the traditional NO-ERROR technique with the newer,
structured error handling that features error objects and CATCH end blocks.
Example
The
following code fragment shows the definition of a variable that
is assigned to the object reference for a new class instance:
DEFINE VARIABLE myCustObj AS CLASS acme.myObjs.CustObj NO-UNDO.
myCustObj = NEW acme.myObjs.CustObj ( ).
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Notes
- After
the assignment, object-reference contains a copy
of the object reference value returned by new-function,
which points to the same object instance, not a copy of the object
created by new-function.
- Although you can assign an object reference to a temp-table
field defined as a Progress.Lang.Object class type, you cannot assign an object reference to
a field in a database table. For more information, see OpenEdge
Development: Object-oriented Programming.
- This statement can raise errors during the execution of constructors for
the class being instantiated by new-function,
or for any class in its inherited class hierarchy. For example:
- A
constructor in the class hierarchy executes the RETURN statement with
the ERROR option or the UNDO statement with
the THROW or RETURN ERROR options.
- The class definition file for the class, a super class, or an
interface could not be found.
- The run-time parameters of the constructor for the class, or
a constructor for a class in the inherited class hierarchy, are
not compatible.
When the AVM encounters one of these
errors, and the constructor cannot create the class instance or
its inherited class hierarchy, the AVM automatically invokes the
destructor for any class that has already been constructed while
building the class hierarchy for the object.
For more information
on errors raised by instantiating classes, see OpenEdge Development:
Object-oriented Programming.
- The ABL Virtual Machine (AVM) automatically deletes (garbage collects)
any class instance that you create with the NEW statement some time
after no reference to that object exists in the ABL session. However, you
can force any class instance to be deleted immediately by using
the DELETE OBJECT statement. For more information on garbage collection for
class instances, see the DELETE OBJECT statement reference entry.