DOCUMENT:Q188817  17-JUL-2001  [visualc]
TITLE   :HOWTO: VC++ MFC Client for the ComCallingJava Sample
PRODUCT :Microsoft C Compiler
PROD/VER:winnt:5.0
OPER/SYS:
KEYWORDS:kbActiveX kbAutomation kbCOMt kbJavaVM kbMFC kbVC500 kbGrpDSJava

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The information in this article applies to:

 - The Microsoft Foundation Classes (MFC), used with:
    - Microsoft Visual C++, 32-bit Enterprise Edition, version 5.0 
    - Microsoft Visual C++, 32-bit Professional Edition, version 5.0 
    - Microsoft virtual machine 
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SUMMARY
=======

Java classes created with the Visual J++ Java compiler can be accessed through
COM. Visual J++ contains a sample that shows how to use COM to call a Java class
from Visual Basic.

It is also possible to call the Java class through Automation using any language.
This article contains steps to create an Automation client using Visual C++ and
MFC.

MORE INFORMATION
================

It is easy to generate a ColeDispatchDriver-derived class in MFC by creating a
new class in ClassWizard using the type library created by Visual J++. However,
to create the Java object and attach the wrapper, you must first call
COleDispatchDriver::CreateDispatch(), then QueryInterface() for the correct
dispinterface.

Calling QueryInterface() is necessary because, by default, Java objects use
AutoIDispatch as the default dispinterface. CreateDispatch() just calls
CoCreateInstance() for IUnknown and then does a QueryInterface() on the IUnknown
for IDispatch. AutoIDispatch assigns DISPIDs during run time and can be used
only when doing late binding.

It is also possible to have the Java object associate the class as the default
dispinterface by implementing an interface called com.ms.com.NoAutoScripting.
This interface does not have any methods associated with it, but tells the VM
(virtual memory) to not make IDispatch available as the default interface
through AutoIDispatch.

Use the following steps to create the client:

1. Follow the steps in the ComCallingJava sample to create a typelib, to create
   a wrapper class, and to build and register the Java class.

2. Create an AppWizard-generated application, either SDI (single-document
   interface) or MDI (multiple-document interface).

3. Initialize OLE by calling AfxOleInit() in CWinApp::InitInstance().

4. Create a COleDispatchDriver wrapper for the Euclid Java class using the type
   library created in step 1. You can do this in ClassWizard by choosing "Add
   Class..." and then "From a type library...".

5. Using ClassWizard, handle the WM_LBUTTONDOWN message in the CView. Use the
   following code as a guide for the button handler:

         //(33B0ECE2-E706-11CF-A0C2-00AA00A71DD8)
         static const CLSID GCDclsid =
            { 0x33B0ECE2, 0xE706, 0x11CF, { 0xa0, 0xC2, 0x0, 0xaa, 0x0, 0xa7,
              0x1d, 0xd8 }};

         // (33B0ECE1-E706-11cf-A0C2-00AA00A71DD8)
         static const CLSID IGCDclsid =
         { 0x33B0ECE1, 0xE706, 0x11CF, { 0xa0, 0xC2, 0x0, 0xaa, 0x0, 0xa7,
           0x1d, 0xd8 }};

         void CComjavaView::OnLButtonDown(UINT nFlags, CPoint point)
         {
            CString str;
            LPDISPATCH pDisp;

            IGCD VJCom;
            VJCom.CreateDispatch(GCDclsid);

            pDisp = VJCom.m_lpDispatch;
            HRESULT hr = pDisp->QueryInterface( IGCDclsid,
                                                (void**)&VJCom.m_lpDispatch);
            if (hr == S_OK)
               pDisp->Release();
            else
               VJCom.m_lpDispatch = pDisp;

            str.Format("The least common denominator of 40 and 24 is %d",
                        VJCom.GCD(40,24));
            AfxMessageBox(str);
            VJCom.ReleaseDispatch();

            CView::OnLButtonDown(nFlags, point);
         }

(c) Microsoft Corporation 1998, All Rights Reserved. Contributions by Kelly Marie
Ward, Microsoft Corporation

Additional query words: QueryInterface AutoIDispatch

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Keywords          : kbActiveX kbAutomation kbCOMt kbJavaVM kbMFC kbVC500 kbGrpDSJava 
Technology        : kbAudDeveloper kbMFC
Version           : winnt:5.0
Issue type        : kbhowto

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