Supported COM data types, and their Java Equivalents

 

WebLogic jCOM supports the full range of COM Automation types. Our philosophy has been to avoid introducing new Java classes in order to access COM types. This means that COM Variants map onto Objects (java.lang.Long, etc.), and Variants containing arrays map onto Java arrays. You won't find a com.bea.jcom.Variant class that you need to use, for example.

WebLogic jCOM also supports accessing some Java collection types as Visual Basic Collections.

Below you will find

• Accessing Java Objects as Visual Basic Collections

• How COM IDL types map to Java, and VC++

• How COM Variants containing different types map to Java

• Type conversions used during late-bound access from COM to Java

• Accessing COM VariantEnums from Java

 

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Accessing Java Objects as Visual Basic Collections

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

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

 

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How COM IDL types map to Java, VB, and VC++

In the following table we show each IDL type, describing its use from Java, from Visual BASIC and from Visual C++.

Table 7-1

IDL	Java	Visual BASIC	Visual C++
[in] VARIANT_BOOL	boolean	ByVal boolean	VARIANT_BOOL
[in, out] or [out] VARIANT_BOOL*	boolean[] single element array	boolean	VARIANT_BOOL*
[in] unsigned char	byte	ByVal byte	unsigned char
[in, out] or [out] unsigned char*	byte[] single element array	byte	unsigned char*
[in] double	double	ByVal Double	double
[in, out] or [out] double*	double[] single element array	double	double*
[in] float	float	ByVal Single	float
[in, out] or [out] float*	float[] single element array	Single	float*
[in] long	int IDL long is 32 bits	ByVal Long>	long>
[in, out] or [out] long*	int[] single element array	Long>	long*
[in] short	short	ByVal Integer>	short>
[in, out] or [out] short*	short[] single element array	Integer	short*
[in] BSTR	java.lang.String	ByVal String	BSTR
[in, out] or [out] BSTR*	java.lang.String[] single element array	String	BSTR*
[in] CY	long CY is fixed point, 64 bit	ByVal Currency	CURRENCY
[in, out] or [out] CY*	long[] single element array	Currency	CURRENCY*
[in] DATE	java.util.Date	ByVal Date	DATE
[in, out] or [out] DATE*	java.util.Date[]	Date	DATE*
[in] IDispatch*	java.lang.Object	ByVal Object	IDispatch*
[in, out] or [out] IDispatch**	java.lang.Object[] single element array	Object	IDispatch**
[in] ISomeInterface*	ISomeInterface Generated Java Interface	ByVal ISomeInterface	ISomeInterface*
[in, out] or [out] ISomeInterface**	ISomeInterface[] single element array	ISomeInterface	ISomeInterface**
[in] SomeClass*	SomeClass Generated Java Class	ByVal SomeClass	SomeClass*
[in, out] or [out] SomeClass**	SomeClass[] single element array	SomeClass	SomeClass**
[in] IUnknown*	java.lang.Object	Specific class/interface	IUnknown*
[in] Variant	java.lang.Object	ByVal Variant	VARIANT
[in, out] or [out] Variant*	java.lang.Object[] single element array	Variant	VARIANT*
[in] SAFEARRAY(unsigned char)	byte[]	not supported by VB	SAFEARRAY*
[in, out] or [out] SAFEARRAY(unsigned char)*	byte[][]	not supported by VB	SAFEARRAY**
[in] SAFEARRAY(VARIANT_BOOL)	boolean[]	not supported by VB	SAFEARRAY*
[in, out] or [out] SAFEARRAY(VARIANT_BOOL)*	boolean[][]	not supported by VB	SAFEARRAY**
[in] SAFEARRAY(short)	short[]	not supported by VB	SAFEARRAY*
[in, out] or [out] SAFEARRAY(short)*	short[][]	not supported by VB	SAFEARRAY**
[in] SAFEARRAY(long)	int[]	not supported by VB	SAFEARRAY*
[in, out] or [out] SAFEARRAY(long)*	int[][]	not supported by VB	SAFEARRAY**
[in] SAFEARRAY(float)	float[]	not supported by VB	SAFEARRAY*
[in, out] or [out] SAFEARRAY(float)*	float[][]	not supported by VB	SAFEARRAY**
[in] SAFEARRAY(double)	double[]	not supported by VB	SAFEARRAY*
[in, out] or [out] SAFEARRAY(double)*	double[][]	not supported by VB	SAFEARRAY**
[in] SAFEARRAY(CURRENCY)	long[]	not supported by VB	SAFEARRAY*
[in, out] or [out] SAFEARRAY(CURRENCY)*	long[][]	not supported by VB	SAFEARRAY**
[in] SAFEARRAY(DATE)	java.util.Date[]	not supported by VB	SAFEARRAY*
[in, out] or [out] SAFEARRAY(DATE)*	java.util.Date[][]	not supported by VB	SAFEARRAY**
[in] SAFEARRAY(BSTR)	String[]	not supported by VB	SAFEARRAY*
[in, out] or [out] SAFEARRAY(BSTR)*	String[][]	not supported by VB	SAFEARRAY**
[in] SAFEARRAY(LPDISPATCH)	Object[]	not supported by VB	SAFEARRAY*
[in, out] or [out] SAFEARRAY(LPDISPATCH)*	Object[][]	not supported by VB	SAFEARRAY**
[in] SAFEARRAY(VARIANT)	Object	not supported by VB	SAFEARRAY*
[in, out] or [out] SAFEARRAY(VARIANT)*	Object[][]	not supported by VB	SAFEARRAY**
[in] SAFEARRAY(LPUNKNOWN)	Object	not supported by VB	SAFEARRAY*
[in, out] or [out] SAFEARRAY(LPUNKNOWN)*	Object[][]	not supported by VB	SAFEARRAY**

 

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How COM Variants containing different types map to Java

The following table shows how Variants are mapped to Java types.

Variant Containing a	Maps to Java type
VARIANT_BOOL	java.lang.Boolean
VARIANT_BOOL*	java.lang.Boolean[] single element array
unsigned char	java.lang.Byte
unsigned char*	java.lang.Byte[] single elment array
double	java.lang.Double
double*	java.lang.Double[] single element array
float	java.lang.Float
float*	java.lang.Float[] single element array
long	java.lang.Integer IDL long is 32 bits
long*	java.lang.Integer[] single element array
short	java.lang.Short
short*	java.lang.Short[] single element array
BSTR	java.lang.String
BSTR*	java.lang.String[]single element array
CY	java.lang.Long
CY*	java.lang.Long[]single element array
Decimal	java.math.BigDecimal
Decimal*	java.math.BigDecimal[]single element array
DATE	java.util.Date
DATE*	java.util.Date[]
SCODE	java.lang.Long
SCODE*	java.lang.Long[] single element array
IDispatch*	java.lang.Object
IUnknown*	java.lang.Object
Single dimensional array of VARIANT_BOOLs	boolean[]
Single dimensional array of unsigned chars	byte[]
Single dimensional array of doubles	double[]
Single dimensional array of floats	float[]
Single dimensional array of longs	int[] IDL long is 32 bits</TD
Single dimensional array of shorts	short[]
Single dimensional array of BSTRs	java.lang.String[]
Single dimensional array of CYs	long[]
Single dimensional array of DATEs	java.util.Date[]
Single dimensional array of SCODEs	long[]
Single dimensional array of IDispatch*s	java.lang.Object[]
Single dimensional array of IUnknown*s	java.lang.Object[]
Single dimensional array of Variants	java.lang.Object[]
Two dimensional array of Variants	java.lang.Object[][]

You can also pass a Variant of type VT_EMPTY or VT_NULL by passing com.bea.jcom.EmptyVariant.TYPE and com.bea.jcom.NullVariant.TYPE.

 

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Type conversions used during late-bound access from COM to Java

These tables show the Java expression used to convert a VB value 'vb' of the VB type on the left to the Java type at the top. Note that conversions marked with a * can also raise Type Mismatch Error.

Java boolean, byte, short and int

Java(across) VB (down)	boolean	byte	short	int
Boolean	natural	vb ? 1 : 0	vb ? 1 : 0	vb ? 1 : 0
Byte(0..255)	vb != 0	new Integer(vb).byteValue()	new Integer(vb).shortValue()	new Integer(vb).intValue()
Integer(16 bit)	vb != 0	new Short(vb).byteValue()	natural	new Short(vb).intValue()
Long(32 bit)	vb != 0	new Integer(vb).byteValue()	new Integer(vb).shortValue()	natural
Single	vb != 0.0F	new Float(vb).byteValue()	new Float(vb).shortValue()	new Float(vb).intValue()
Double	vb != 0.0	new Double(vb).byteValue()	new Double(vb).shortValue()	new Double(vb).intValue()
Currency(64 bit)	vb != 0	new Long(vb).byteValue()	new Long(vb).shortValue()	new Long(vb).intValue()
String	new Boolean(vb).booleanValue()	new Long(vb).byteValue()*	new Long(vb).shortValue()*	new Long(vb).intValue()*
Date	Type Mismatch Error	Type Mismatch Error	Type Mismatch Error	Type Mismatch Error
Object	Type Mismatch Error	Type Mismatch Error	Type Mismatch Error	Type Mismatch Error
Variants	As above depending on content

Java long, char, float and double

VB/Java	long	char	float	double
Boolean	vb ? 1 : 0	vb ? (char)1 : (char)0	vb ? 1.0F : 0.0F	vb ? 1.0 : 0.0
Byte(0..255)	new Integer(vb).longValue()	(char)(new Integer(vb).intValue())	new Integer(vb).floatValue()	new Integer(vb).doubleValue()
Integer(16 bit)	new Short(vb).longValue()	(char)(new Short(vb).intValue())	new Short(vb).floatValue()	new Short(vb).doubleValue()
Long(32 bit)	new Integer(vb).longValue()	(char)(new Integer(vb).byteValue())	new Integer(vb).floatValue()	new Integer(vb).doubleValue()
Single	new Float(vb).longValue()	(char)(new Float(vb).intValue())	natural	new Float(vb).doubleValue()
Double	new Double(vb).longValue()	(char)(new Double(vb).intValue())	new Double(vb).floatValue()	natural
Currency(64 bit)	natural	(char)(new Long(vb).intValue())	new Long(vb).floatValue()	new Long(vb).doubleValue()
String	new Long(vb).longValue()	(char)(new Long(vb).intValue())	new Long(vb).floatValue()	new Long(vb).doubleValue()
Date	Type Mismatch Error	Type Mismatch Error	Type Mismatch Error	Type Mismatch Error
Object	Error	Error	Error	Error
Variants	As above depending on content

Java String, Date and Object

VB/Java	String	Date	Object
Boolean	vb + ""	Error	new Boolean(vb)
Byte(0..255)	vb + ""	Error	new Byte(vb)
Integer(16 bit)	vb + ""	Error	new Short(vb)
Long(32 bit)	vb + ""	Error	new Integer(vb)
Single	vb + ""	Error	new Float(vb)
Double	vb + ""	Error	new Double(vb)
Currency	vb + ""	Error	new Long(vb)
String	natural	new Date(vb)	vb (as String_
Date	vb.toString()	Natural	vb (as Date)
Object	vb.toString	Error	vb
Variant	As above depending on content

Arrays

If a Java method has a parameter which is an array, then if you pass a VB parameter by value to that method you will get an error. If you pass a value by reference, and if the type matches precisely (see below), the Java method will receive a single element array whose single element can be modified to change the corresponding VB parameter. If you pass an array, and if the array content type matches precisely, the Java method will receive an array whose elements can be modified to change the corresponding VB parameter.

Java type	VB pass by reference match
boolean[]	Boolean passed by reference
byte[]	Byte passed by reference
short[]	Short passed by reference
int[]	Long passed by reference
long[]	Currency passed by reference
float[]	Single passed by reference
double[]	Double passed by reference
String[]	String passed by reference
java.util.Date[]	Date passed by reference

Arrays:

Java type	Parameter of this VB type will match
boolean[]	Dim anArray(n) as Boolean
byte[]	Dim anArray(n) as Byte
short[]	Dim anArray(n) as Short
int[]	Dim anArray(n) as Long
long[]	Dim anArray(n) as Currency
float[]	Dim anArray(n) as Single
double[]	Dim anArray(n) as Double
String[]	Dim anArray(n) as String
java.util.Date[]	Dim anArray(n) as Date
Object[]	Dim anArray(n) as String
Object[]	Dim anArray(n) as Date
Object[]	Dim anArray(n) as Object
Object[]	Dim anArray(n) as Variant

 

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Accessing COM VariantEnums from Java

Some COM methods return a COM VariantEnumeration type. WebLogic jCOM's java2com tool automatically converts the returned type into a standard Java java.lang.Enumeration. There isn't a perfect match though, since COM Enumerations have no equivalent to the 'hasMoreElements()' call, meaning that you have to keep on doing 'nextElement' until you get a 'NoSuchElementException'.

We do provide a workaround -- if you set the JCOM_PREFETCH_ENUMS Java property, WebLogic jCOM will pre-fetch the next element behind the scenes, and thus allow the 'hasMoreElements()' method to work properly.