Accessing Java objects as Visual Basic Collections

Visual Basic has a built-in COM class called Collection. J-Integra® provides support for accessing instances of java.util.Vector and java.util.List as VB Collections.

Create the Java Bridge

Just as was demonstrated in the VB-EJB examples, we will create a simple briding application that will return a java.util.LinkedList object that can be used in Visual Basic as Collection. 

The first step is to to Register the JVM. 

> D:\jintegra\bin\regjvmcmd.exe firstjvm localhost[7050]

Next create the Java Briging application:

This is the Main Java class. As you can see, it does nothing apart from register the JVM:

// This is the bridge. The VB client talks to this  
// process via DCOM, and this process talks to WebLogic via RMI. It all happens  
// behind the scenes in the J-Integra® runtime.  
 
import java.util.*; 
 
import com.linar.jintegra.*; 
 
public class Main { 
  public static void main(String[] args) throws Exception { 
    // Tell the J-Integra® Activator on the localhost that this JVM is alive, ready to receive  
    // remote requests, and it is called "firstjvm".  
    com.linar.jintegra.Jvm.register("firstjvm"); 
    Thread.sleep(6000000); // Sleep for an hour  
  } 
}

Cut and paste the above class from your Web browser into the Main.java file, build it using the javac Main.java.

Now run the bridge, setting the JINTEGRA_DCOM_PORT property to 7050

> java -DJINTEGRA_DCOM_PORT=7050 Main

Example Visual BASIC code

Private Sub Form_Load() Dim c As Collection Set c = GetObject("firstjvm:java.util.LinkedList") c.Add "hello" ' List is now: "hello" c.Add Now, , "hello" ' List is now: , "hello" c.Add "Goodbye", , , "hello" ' List is now: now, "hello", "Goodbye" c.Add "Before", , 3 ' List is now: now, "hello", "Before", "Goodbye" c.Add "After", , , 4 ' List is now: now, "hello", "Before", "Goodbye", "After" For Each e In c MsgBox e Next c.Remove 2 ' List is now: now, "Before", "Goodbye", "After" c.Remove "Goodbye" ' List is now: now, "Before", "After" MsgBox c.Item(1) MsgBox c.Count End Sub

VB	Maps to java.util.Vector	Notes
Collection.Add(item)	aVector.addElement(item)
Collection.Add(item, , before)	aVector.insertElementAt(before - 1, item)	if before is a number
Collection.Add(item, , before)	aVector.insertElementAt(aVector.indexOf(before), item)	if before is not a number
Collection.Add(item, , , after)	aVector.insertElementAt(after, item)	if after is not a number
Collection.Add(item, , , after)	aVector.insertElementAt(aVector.indexOf(after) + 1, item)	if after is a number
Collection.Count	aVector.size()
Collection.Item(index)	aVector.elementAt(index - 1)	index must be a number
Collection.Remove(index)	aVector.removeElementAt(index - 1)	if index is a number
Collection.Remove(index)	aVector.removeElement(index)	if index is not a number
For Each x in aCollection	x will take on the value of each object in the aVector.elements() enumeration

VB	Maps to java.util.List	Notes
Collection.Add(item)	aList.target.add(item)
Collection.Add(item, , before)	aList.add(before - 1, item)	if before is a number
Collection.Add(item, , before)	aList.add(aVector.indexOf(before), item)	if before is not a number
Collection.Add(item, , , after)	aList.add(after, item)	if after is not a number
Collection.Add(item, , , after)	aList.add(aVector.indexOf(after) + 1, item)	if after is a number
Collection.Count	aList.size()
Collection.Item(index)	aList.get(index - 1)	index must be a number
Collection.Remove(index)	aList.remove(index - 1)	if index is a number
Collection.Remove(index)	aList.remove(index)	if index is not a number
For Each x in aCollection	x will take on the value of each object in the aList.listIterator() iterator