DynamicCast

Description

Converts an instantiated PowerBuilder proxy object to a proxy for
the passed-in proxy name.

Syntax

javavm.DynamicCast(powerobject proxyobject, readonly string proxyname)

1	javavm.DynamicCast(powerobject proxyobject, readonly string proxyname)

Argument	Description
javavm	An instance of the JavaVM class
proxyobject	An instantiated PowerBuilder proxy object
proxyname	A string containing the name of the proxy to be instantiated

Return value

Powerobject.

A new proxy object for the Java class referenced by proxyname.
This method returns null if the proxy cannot be created.

Examples

In the following example, the object returned from the
nextElement method is represented by a proxy for the Employee class.
The GetActualClass method is used to determine whether the object is
actually a SalariedEmployee, and if it is, the proxy px_Employee is
down cast to the proxy px_SalariedEmployee so that the adjustSalary
method can be called:

DepartmentHome   px_DeptHome
Department       px_Dept
Enumeration      px_EmployeeList
Employee         px_Employee
Salaried         px_SalariedEmployee
Contract         px_ContractEmployee
EJBConnection    conn

conn = create ejbconnection
try
   conn.connectToServer(properties)
   px_DeptHome = conn.lookup("DepartmentHome",  &amp;
      "Department",   &amp;
      "com.joesportinggoods.ejbs.DepartmentHome")
   px_Dept = px_DeptHome.findByPrimaryKey(as_DeptName)

   px_EmployeeList = px_Dept.getEmployees()
   DO WHILE px_EmployeeList.hasMoreElements()
     px_Employee = px_EmployeeList.nextElement()
     IF i_jvm.getActualClass(px_Employee) =  &amp;
        "com.joesportinggoods.ejbs.Salaried" THEN
         px_SalariedEmployee =   &amp;
            i_jvm.dynamicCast(px_Employee, "Salaried")
         px_SalariedEmployee.adjustSalary(al_increase)
     END IF
   LOOP
catch (Exception e)
   THROW CREATE ApplyRaiseException
end try

DepartmentHome px_DeptHome

Department px_Dept

Enumeration px_EmployeeList

Employee px_Employee

Salaried px_SalariedEmployee

Contract px_ContractEmployee

EJBConnection conn

conn = create ejbconnection

try

conn.connectToServer(properties)

px_DeptHome = conn.lookup("DepartmentHome", &

"Department", &

"com.joesportinggoods.ejbs.DepartmentHome")

px_Dept = px_DeptHome.findByPrimaryKey(as_DeptName)

px_EmployeeList = px_Dept.getEmployees()

DO WHILE px_EmployeeList.hasMoreElements()

px_Employee = px_EmployeeList.nextElement()

IF i_jvm.getActualClass(px_Employee) = &

"com.joesportinggoods.ejbs.Salaried" THEN

px_SalariedEmployee = &

i_jvm.dynamicCast(px_Employee, "Salaried")

px_SalariedEmployee.adjustSalary(al_increase)

END IF

LOOP

catch (Exception e)

THROW CREATE ApplyRaiseException

end try

In this example, getAllItems returns a java.lang.Object in the
EJB declaration, which maps to the PowerBuilder Any data type. The
call to GetInterfaces determines whether what is returned is a
java.util.List. If it is, a call to DynamicCast obtains a proxy for
List, which is used to obtain the size of the list before using its
Get method to obtain the elements of the list. A method such as
getAllItems can be used in many situations, such as to get a list of
part numbers for any type of product.

ItemManagerHome px_ItemMgrHome
ItemManager px_ItemMgr
Item px_Item
List px_ItemList
any any_Object
boolean ib_isAList = FALSE
string is_IFs[]
string is_actualClass
long ll_row

TRY
   px_ItemMgrHome =      g_EJBConn.Lookup("ItemManagerHome", &amp;
     "ItemManager","com.xapic.ItemManagerHome")
   px_ItemMgr = px_ItemMgrHome.create()
   any_Object = px_ItemMgr.getAllItems()
// check if object implements java.util.List interface
   integer i
   FOR i = 1 to g_javaVM.getInterfaces(any_Object, &amp;
     is_IFs)
     IF is_IFs[i] = "java.util.List" THEN
        ib_isAList = TRUE
        EXIT
     END IF
   NEXT
   // if it is a list
   IF ib_isAList THEN
     px_ItemList = g_javaVM.dynamicCast(any_Object, &amp;
        "list")
     // traverse the list
      FOR i = 0 TO px_ItemList.size() - 1
        // get item on the list
        any_Object = px_ItemList.get(i)
         // determine its class and dynamically cast it
        is_actualClass = &amp;
           g_javaVM.getActualClass(any_Object)
        is_actualClass = Mid(is_actualClass, &amp;
           LastPos(is_actualClass,".") + 1, &amp;
           Len(is_actualClass))
        px_Item = g_javaVM.dynamicCast(any_Object,            is_actualClass)
        // add item to datastore
        ll_row = ads_Items.insertRow(0)
        ads_Items.object.id[ll_row] = px_Item.getID()
        ads_Items.object.type[ll_row] = is_actualClass
      NEXT
   END IF
CATCH (Throwable t)
   // Handle exception
END TRY

ItemManagerHome px_ItemMgrHome

ItemManager px_ItemMgr

Item px_Item

List px_ItemList

any any_Object

boolean ib_isAList = FALSE

string is_IFs[]

string is_actualClass

long ll_row

TRY

px_ItemMgrHome = g_EJBConn.Lookup("ItemManagerHome", &

"ItemManager","com.xapic.ItemManagerHome")

px_ItemMgr = px_ItemMgrHome.create()

any_Object = px_ItemMgr.getAllItems()

// check if object implements java.util.List interface

integer i

FOR i = 1 to g_javaVM.getInterfaces(any_Object, &

is_IFs)

IF is_IFs[i] = "java.util.List" THEN

ib_isAList = TRUE

EXIT

END IF

// if it is a list

IF ib_isAList THEN

px_ItemList = g_javaVM.dynamicCast(any_Object, &

"list")

// traverse the list

FOR i = 0 TO px_ItemList.size() - 1

// get item on the list

any_Object = px_ItemList.get(i)

// determine its class and dynamically cast it

is_actualClass = &

g_javaVM.getActualClass(any_Object)

is_actualClass = Mid(is_actualClass, &

LastPos(is_actualClass,".") + 1, &

Len(is_actualClass))

px_Item = g_javaVM.dynamicCast(any_Object, is_actualClass)

// add item to datastore

ll_row = ads_Items.insertRow(0)

ads_Items.object.id[ll_row] = px_Item.getID()

ads_Items.object.type[ll_row] = is_actualClass

END IF

CATCH (Throwable t)

// Handle exception

END TRY

Usage

There are two scenarios in which a Java object returned from a
call to an EJB method can be represented by a proxy that does not
provide the methods you need:

If the class of a Java object returned from an EJB method call
is dynamically generated, PowerBuilder uses a proxy for the first
interface implemented by the Java class.
The prototype of an EJB method that actually returns
someclass can be defined to return a class that someclass extends or
implements.

For example, the prototype of a method that actually returns
an object of type java.util.ArrayList can be defined to return
java.util.Collection instead. (The java.util.ArrayList class
inherits from java.util.AbstractList, which inherits from
java.util.AbstractCollection, which implements
java.util.Collection.) If the method prototype has a return type of
java.util.Collection, PowerBuilder uses a proxy for
java.util.Collection.

The DynamicCast method allows you to cast the returned proxy
object to a proxy for the interface you require, or for the actual class
of the object returned at runtime so that the methods of that object can
be used.

You can obtain the actual class of the object using the
GetActualClass method. You can also use the DynamicCast method with the
GetSuperClass method, which returns the immediate parent of the Java
class, and the GetInterfaces method, which writes a list of interfaces
implemented by the class to an array of strings.

For example, consider the following class:

public class java.util.LinkedList extends java.util.AbstractSequentialList implements java.util.List, java.lang.Cloneable, java.io.Serializable

1	public class java.util.LinkedList extends java.util.AbstractSequentialList implements java.util.List, java.lang.Cloneable, java.io.Serializable

GetActualClass returns java.util.LinkedList, GetSuperClass returns
java.util.AbstractSequentialList, and GetInterfaces returns 3 and writes
three strings to the referenced string array: java.util.List,
java.lang.Cloneable, and java.io.Serializable.

See also

Document get from Powerbuilder help

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Powerbuilder Documentation 2018

August 20, 2023

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