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ABL Reference
ABL Syntax Reference : NEW statement
 

NEW statement

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 ]
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:
*A temp-table field defined as a Progress.Lang.Object class type using the DEFINE TEMP-TABLE statement
*A variable scoped to the current procedure, user-defined function, or method of a class or an accessible class-based variable data member defined as a class or interface type using the DEFINE VARIABLE statement
*A parameter defined as a class or interface type for the current procedure, user-defined function, or method of a class using an appropriate DEFINE PARAMETER statement or Parameter definition syntax
*An accessible and writable class-based property defined as a class or interface type using the DEFINE PROPERTY statement
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 ]...] )
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 ( ).

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.

See also

Assignment (=) statement, CAST function, Class-based object reference, CLASS statement, DYNAMIC-NEW statement, NEW function (classes), New( ) method, Parameter passing syntax