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Can JNA be used for a complex Windows DLL like IMAPI

I've managed to get COM4J to use some functionality in the windows IMAPI (CD writing).
However I've failed to get any of the calls that return SAFEARRAYs working, but this project doesn't appear to be currently active ...
The DLL is usually in C:\Windows\System32\imapi2.dll, and using it also requires using C:\Windows\System32\imapi2fs.dll
Looking around for a JAVA-COM bridge project that is active led me to JNA.
The remit of the project to simplify JAVA-COM bridging intrigued me .... however I fell at the first hurdle, and am hoping someone can help.
So far I've taken the Microsoft IMAPI examples and written a Powershell application, from which I have the series of calls I need to make to the API.[CDInterface][1]
The first thing you need to do with IMAPI is create an Instance of IDiskMaster2, so I've declared that via an Imapi2 interface, like so
public interface Imapi2 extends Library {
Imapi2 INSTANCE = (Imapi2)
Native.load("C:/Windows/System32/imapi2.dll" , Imapi2.class);
public static class IDiscMaster2 extends Structure {
int getCount;
public int getCount() {
return getCount;
}
}
IDiscMaster2 createMsftDiscMaster2();
}
Then in the main code
Imapi2.IDiscMaster2 recorderList = Imapi2.INSTANCE.createMsftDiscMaster2();
System.out.println("Found " + recorderList.getCount() + " Recorders");
Just putting 'imapi2' in the call to Native.load() didn't work either.
I'm guessing I'm doing something fundamentally wrong, but it's not clear how you get JNA to 'see' a new dll you want to interface to ..... and also I am kind of afraid there is something very different about this API from the othe APIs that people are using JNA to talk to, so may not be worth trying!
public interface Imapi2 extends Library {
Imapi2 INSTANCE = (Imapi2)
Native.load("C:/Windows/System32/imapi2.dll" , Imapi2.class);
public class IDiscMaster2 extends Dispatch {
public static final CLSID CLSID_MsftDiscMaster2 = new CLSID("2735412F-7F64-5B0F-8F00-5D77AFBE261E");
public IDiscMaster2() {
}
private IDiscMaster2(Pointer pvInstance) {
super(pvInstance);
}
public static IDiscMaster2 create() {
PointerByReference pbr = new PointerByReference();
WinNT.HRESULT hres = Ole32.INSTANCE.CoCreateInstance(CLSID_MsftDiscMaster2, null, WTypes.CLSCTX_ALL, null, pbr);
if (COMUtils.FAILED(hres)) {
System.out.println("ERROR: Failed to create instance");
return null;
}
return new IDiscMaster2(pbr.getValue());
}
public WinNT.HRESULT _getCount(Pointer count ){
return (WinNT.HRESULT) _invokeNativeObject(2, new Object[]{count}, WinNT.HRESULT.class);
}
public long getCount() {
try {
long count = -1;
Pointer ptr = new Pointer(count);
WinNT.HRESULT result = _getCount(ptr);
COMUtils.checkRC(result);
return count;
} catch ( Exception e ) {
System.out.println("Error : " + e.getMessage());
}
return -1;
}
}
Then invocation in main changed to
Imapi2 imapi2Lib = Imapi2.INSTANCE;
Imapi2.IDiscMaster2 recorderList = new Imapi2.IDiscMaster2();
System.out.println("Found " + recorderList.getCount() + " Recorders");
IntelliJ shows up uninvoked methods, so it doesn't look like create() is getting called. Not sure if this is because I need to call it, or down to the function implementing IDispatch not IUnknown.
[1]: https://github.com/nosdod/CDInterface

I've answered this in a similar question which I originally marked this as a duplicate of. However, given the difficulty loading this, your case is unique enough that I'll attempt to give a separate answer.
The general case for COM is that there is an API function that creates the object. You have mapped this as createMsftDiscMaster2(). Note that you have allocated a resource here and it needs to be disposed of when you are done with it; the API documentation should tell you how to do that (possibly by calling Release() from IUnknown.)
Your next step is to map the IDiscMaster2 COM class. I see two mappings here, so I'm confused as to which one you want. The one at the top of your question is incorrect, but the one extending Dispatch later is the correct way to start, but I'm not clear where you've gone after that. The rest of the class should look similar to the internals of the Dispatch class in JNA.
In that class you can see the boilerplate that you will follow. Note that it extends Unknown which follows the same boilerplate for offsets 0, 1, and 2 for the first 3 COM functions QueryInterface, AddRef, and Release. Dispatch picks up with offsets 3, 4, 5, and 6 for COM functions GetTypeInfoCount, GetTypeInfo, GetIDsOfNames, and Invoke.
So in your mapping for DiskMaster2 you will pick up with offset 7, and your mapping will look like:
public HRESULT TheFunctionName(FOO foo, BAR bar) {
return (HRESULT) this._invokeNativeObject(7,
new Object[] { this.getPointer(), foo, bar },
HRESULT.class);
}
This is where you need to locate the actual header file for this class to determine the order in which the functions appear in the Vtbl. It looks like you attempted to do this with your code, but the offset 2 is already assigned in Unknown, the lowest one you'll be able to use is 7 (and continue on with 8, 9, 10 for each function in this COM interface, in the correct order -- which you must determine from the Vtbl.)
Based on this header, you can see those functions mapped in order and your offsets should be: 7: get__NewEnum, 8: get_Item, 9: get_Count, and 10: get_IsSupportedEnvironment. Use those header function mappings as a start and change them to the _invokeNativeObject() format above. (They all return HRESULT, you'll just be changing the argument list.)

Java constructor creates many null instances before the required object

this is my first question on here and I did a search before forming it, so I hope everything is as required.
I am working on a school assignment in Java. I am able to produce the required output but there are a lot of null instances created first. I don't understand why. Information about the library the professor created for the course and the code are below
Library included with this course: i2c.jar. It can be found here.
included in this Library are the classes Country and CountryDB. The API for the Country class can be found at http://130.63.94.24/~roumani/book/doc/i2c/ca/roumani/i2c/Country.html
The API for the CountryDB class can be found at http://130.63.94.24/~roumani/book/doc/i2c/ca/roumani/i2c/CountryDB.html
I am asked to create a class called Game, using the Country and CountryDB APIs.
The only attribute is db, which is an instance of CountryDB.
The constructor only sets the attribute (db) for this instance to a new CountryDB object.
The class is also meant to include a method (called qa) that follows this pseudocode:
get a reference to the database's capital city list
determine the size of this list. Cal it n.
generate a random number in [0,n) called index.
invoke get(index) on the list to get a random capital city. Call it c
get a reference to the database's data map
invoke get(c) on the map to get a reference to a country. Call it ref.
The method is then supposed to return one of two Strings (which will be clear in the code). Everything works as it should, except I get a lot of "nulls" before the desired output. When made into a List, db has size 241 so I suspect I am creating 241 null instances and 1 proper instance. I have no idea why though. I have tested every line of code in my method and the constructor was dictated by the textbook.
CODE
package ca.yorku.eecs.caps;
import java.util.List;
import java.util.Map;
import ca.roumani.i2c.Country;
import ca.roumani.i2c.CountryDB;
public class Game
{
private CountryDB db;
public Game()
{
this.db = new CountryDB();
}
public String qa()
{
List<String> capitals = db.getCapitals();
System.out.println(capitals.toString());
int n = capitals.size();
System.out.println(n);
int index = ((int) (n * Math.random()));
System.out.println(index);
String c = capitals.get(index);
System.out.println(c);
Map<String, Country> data = db.getData();
Country ref = data.get(c);
if (Math.random() > 0.5)
{
return "What is the capital of " + ref.getName() + "? \n" + ref.getCapital();
}
else
{
return ref.getCapital() + " is the capital of? \n" + ref.getName();
}
}
public static void main(String[] args)
{
Game g = new Game();
System.out.println(g.qa());
}
}
the System.out.println() statements are only there to test when the nulls occur. It clearly happens immediately because my psvm output is 241 nulls (on separate lines) followed by my desired output. Can somebody please tell me what I am doing wrong?
And, more generally (to help more people) how do you implement classes, the constructor of which instantiates another class and sets it as an attribute value?
I appreciate any help. Also, please note, I am not trying to get others to do my work for me. I've spent hours on this and my lab TA also wasn't sure why it happens either. He would have helped me correct it had he known how.
Thank you.

Java class: limit instance variable to one of several possible values, depending on other instance variables

I am sorry for the vague question. I am not sure what I'm looking for here.
I have a Java class, let's call it Bar. In that class is an instance variable, let's call it foo. foo is a String.
foo cannot just have any value. There is a long list of strings, and foo must be one of them.
Then, for each of those strings in the list I would like the possibility to set some extra conditions as to whether that specific foo can belong in that specific type of Bar (depending on other instance variables in that same Bar).
What approach should I take here? Obviously, I could put the list of strings in a static class somewhere and upon calling setFoo(String s) check whether s is in that list. But that would not allow me to check for extra conditions - or I would need to put all that logic for every value of foo in the same method, which would get ugly quickly.
Is the solution to make several hundred classes for every possible value of foo and insert in each the respective (often trivial) logic to determine what types of Bar it fits? That doesn't sound right either.
What approach should I take here?
Here's a more concrete example, to make it more clear what I am looking for. Say there is a Furniture class, with a variable material, which can be lots of things, anything from mahogany to plywood. But there is another variable, upholstery, and you can make furniture containing cotton of plywood but not oak; satin furniture of oak but not walnut; other types of fabric go well with any material; et cetera.

I wouldn't suggest creating multiple classes/templates for such a big use case. This is very opinion based but I'll take a shot at answering as best as I can.
In such a case where your options can be numerous and you want to keep a maintainable code base, the best solution is to separate the values and the logic. I recommend that you store your foo values in a database. At the same time, keep your client code as clean and small as possible. So that it doesn't need to filter through the data to figure out which data is valid. You want to minimize dependency to data in your code. Think of it this way: tomorrow you might need to add a new material to your material list. Do you want to modify all your code for that? Or do you want to just add it to your database and everything magically works? Obviously the latter is a better option. Here is an example on how to design such a system. Of course, this can vary based on your use case or variables but it is a good guideline. The basic rule of thumb is: your code should have as little dependency to data as possible.
Let's say you want to create a Bar which has to have a certain foo. In this case, I would create a database for BARS which contains all the possible Bars. Example:
ID NAME FOO
1 Door 1,4,10
I will also create a database FOOS which contains the details of each foo. For example:
ID NAME PROPERTY1 PROPERTY2 ...
1 Oak Brown Soft
When you create a Bar:
Bar door = new Bar(Bar.DOOR);
in the constructor you would go to the BARS table and query the foos. Then you would query the FOOS table and load all the material and assign them to the field inside your new object.
This way whenever you create a Bar the material can be changed and loaded from DB without changing any code. You can add as many types of Bar as you can and change material properties as you goo. Your client code however doesn't change much.
You might ask why do we create a database for FOOS and refer to it's ids in the BARS table? This way, you can modify the properties of each foo as much as you want. Also you can share foos between Bars and vice versa but you only need to change the db once. cross referencing becomes a breeze. I hope this example explains the idea clearly.

You say:
Is the solution to make several hundred classes for every possible
value of foo and insert in each the respective (often trivial) logic
to determine what types of Bar it fits? That doesn't sound right
either.
Why not have separate classes for each type of Foo? Unless you need to define new types of Foo without changing the code you can model them as plain Java classes. You can go with enums as well but it does not really give you any advantage since you still need to update the enum when adding a new type of Foo.
In any case here is type safe approach that guarantees compile time checking of your rules:
public static interface Material{}
public static interface Upholstery{}
public static class Oak implements Material{}
public static class Plywood implements Material{}
public static class Cotton implements Upholstery{}
public static class Satin implements Upholstery{}
public static class Furniture<M extends Material, U extends Upholstery>{
private M matrerial = null;
private U upholstery = null;
public Furniture(M matrerial, U upholstery){
this.matrerial = matrerial;
this.upholstery = upholstery;
}
public M getMatrerial() {
return matrerial;
}
public U getUpholstery() {
return upholstery;
}
}
public static Furniture<Plywood, Cotton> cottonFurnitureWithPlywood(Plywood plywood, Cotton cotton){
return new Furniture<>(plywood, cotton);
}
public static Furniture<Oak, Satin> satinFurnitureWithOak(Oak oak, Satin satin){
return new Furniture<>(oak, satin);
}

It depends on what you really want to achieve. Creating objects and passing them around will not magically solve your domain-specific problems.
If you cannot think of any real behavior to add to your objects (except the validation), then it might make more sense to just store your data and read them into memory whenever you want. Even treat rules as data.
Here is an example:
public class Furniture {
String name;
Material material;
Upholstery upholstery;
//getters, setters, other behavior
public Furniture(String name, Material m, Upholstery u) {
//Read rule files from memory or disk and do all the checks
//Do not instantiate if validation does not pass
this.name = name;
material = m;
upholstery = u;
}
}
To specify rules, you will then create three plain text files (e.g. using csv format). File 1 will contain valid values for material, file 2 will contain valid values for upholstery, and file 3 will have a matrix format like the following:
upholstery\material plywood mahogany oak
cotton 1 0 1
satin 0 1 0
to check if a material goes with an upholstery or not, just check the corresponding row and column.
Alternatively, if you have lots of data, you can opt for a database system along with an ORM. Rule tables then can be join tables and come with extra nice features a DBMS may provide (like easy checking for duplicate values). The validation table could look something like:
MaterialID UpholsteryID Compatability_Score
plywood cotton 1
oak satin 0
The advantage of using this approach is that you quickly get a working application and you can decide what to do as you add new behavior to your application. And even if it gets way more complex in the future (new rules, new data types, etc) you can use something like the repository pattern to keep your data and business logic decoupled.
Notes about Enums:
Although the solution suggested by #Igwe Kalu solves the specific case described in the question, it is not scalable. What if you want to find what material goes with a given upholstery (the reverse case)? You will need to create another enum which does not add anything meaningful to the program, or add complex logic to your application.

This is a more detailed description of the idea I threw out there in the comment:
Keep Furniture a POJO, i.e., just hold the data, no behavior or rules implemented in it.
Implement the rules in separate classes, something along the lines of:
interface FurnitureRule {
void validate(Furniture furniture) throws FurnitureRuleException;
}
class ValidMaterialRule implements FurnitureRule {
// this you can load in whatever way suitable in your architecture -
// from enums, DB, an XML file, a JSON file, or inject via Spring, etc.
private Set<String> validMaterialNames;
#Overload
void validate(Furniture furniture) throws FurnitureRuleException {
if (!validMaterialNames.contains(furniture.getMaterial()))
throws new FurnitureRuleException("Invalid material " + furniture.getMaterial());
}
}
class UpholsteryRule implements FurnitureRule {
// Again however suitable to implement/config this
private Map<String, Set<String>> validMaterialsPerUpholstery;
#Overload
void validate(Furniture furniture) throws FurnitureRuleException {
Set<String> validMaterialNames = validMaterialsPerUpholstery.get(furniture.getUpholstery();
if (validMaterialNames != null && !validMaterialNames.contains(furniture.getMaterial()))
throws new FurnitureRuleException("Invalid material " + furniture.getMaterial() + " for upholstery " + furniture.getUpholstery());
}
}
// and more complex rules if you need to
Then have some service along the lines of FurnitureManager. It's the "gatekeeper" for all Furniture creation/updates:
class FurnitureManager {
// configure these via e.g. Spring.
private List<FurnitureRule> rules;
public void updateFurniture(Furniture furniture) throws FurnitureRuleException {
rules.forEach(rule -> rule.validate(furniture))
// proceed to persist `furniture` in the database or whatever else you do with a valid piece of furniture.
}
}

material should be of type Enum.
public enum Material {
MAHOGANY,
TEAK,
OAK,
...
}
Furthermore you can have a validator for Furniture that contains the logic which types of Furniture make sense, and then call that validator in every method that can change the material or upholstery variable (typically only your setters).
public class Furniture {
private Material material;
private Upholstery upholstery; //Could also be String depending on your needs of course
public void setMaterial(Material material) {
if (FurnitureValidator.isValidCombination(material, this.upholstery)) {
this.material = material;
}
}
...
private static class FurnitureValidator {
private static boolean isValidCombination(Material material, Upholstery upholstery) {
switch(material) {
case MAHOGANY: return upholstery != Upholstery.COTTON;
break;
//and so on
}
}
}
}

We often are oblivious of the power inherent in enum types. The Java™ Tutorials clearly states "you should use enum types any time you need to represent a fixed set of constants."
How do you simply make the best of enum in resolving the challenge you presented? - Here goes:
public enum Material {
MAHOGANY( "satin", "velvet" ),
PLYWOOD( "leather" ),
// possibly many other materials and their matching fabrics...
OAK( "some other fabric - 0" ),
WALNUT( "some other fabric - 0", "some other fabric - 1" );
private final String[] listOfSuitingFabrics;
Material( String... fabrics ) {
this.listOfSuitingFabrics = fabrics;
}
String[] getListOfSuitingFabrics() {
return Arrays.copyOf( listOfSuitingFabrics );
}
public String toString() {
return name().substring( 0, 1 ) + name().substring( 1 );
}
}
Let's test it:
public class TestMaterial {
for ( Material material : Material.values() ) {
System.out.println( material.toString() + " go well with " + material.getListOfSuitingFabrics() );
}
}

Probably the approach I'd use (because it involves the least amount of code and it's reasonably fast) is to "flatten" the hierarchical logic into a one-dimensional Set of allowed value combinations. Then when setting one of the fields, validate that the proposed new combination is valid. I'd probably just use a Set of concatenated Strings for simplicity. For the example you give above, something like this:
class Furniture {
private String wood;
private String upholstery;
/**
* Set of all acceptable values, with each combination as a String.
* Example value: "plywood:cotton"
*/
private static final Set<String> allowed = new HashSet<>();
/**
* Load allowed values in initializer.
*
* TODO: load allowed values from DB or config file
* instead of hard-wiring.
*/
static {
allowed.add("plywood:cotton");
...
}
public void setWood(String wood) {
if (!allowed.contains(wood + ":" + this.upholstery)) {
throw new IllegalArgumentException("bad combination of materials!");
}
this.wood = wood;
}
public void setUpholstery(String upholstery) {
if (!allowed.contains(this.wood + ":" + upholstery)) {
throw new IllegalArgumentException("bad combination of materials!");
}
this.upholstery = upholstery;
}
public void setMaterials(String wood, String upholstery) {
if (!allowed.contains(wood + ":" + upholstery)) {
throw new IllegalArgumentException("bad combination of materials!");
}
this.wood = wood;
this.upholstery = upholstery;
}
// getters
...
}
The disadvantage of this approach compared to other answers is that there is no compile-time type checking. For example, if you try to set the wood to plywoo instead of plywood you won’t know about your error until runtime. In practice this disadvantage is negligible since presumably the options will be chosen by a user through a UI (or through some other means), so you won’t know what they are until runtime anyway. Plus the big advantage is that the code will never have to be changed so long as you’re willing to maintain a list of allowed combinations externally. As someone with 30 years of development experience, take my word for it that this approach is far more maintainable.
With the above code, you'll need to use setMaterials before using setWood or setUpholstery, since the other field will still be null and therefore not an allowed combination. You can initialize the class's fields with default materials to avoid this if you want.

How to scan an object in java?

I am making exactly the same Java program that is in this link:
Run-time Polymorphism in Java without "abstract"?
But I am having problems in the Main Application.
In my problem I have to ask the user to enter which types does he want(Bicycle,MountainBike,RoadBike).
And then I add what type he chose to an array of 5 indexes.
How can I do that?
Please give me some help.
Thanks in advance.

I don't know how you look for answers from your users, but if it's buttons you do it with, you can just add the requested type of object, when a user press specific buttons.
But what you have to do, is make an ArrayList<Bicycle> and then just add the objects that extends Bicycle.

You should create a factory method that returns an instance of a Bicycle:
For example:
public Bicycle createBicycle(String type) {
if (type.equals("Bicycle")) {
return new Bicycle(20, 10, 1);
} else if (type.equals("MountainBike")) {
return new MountainBike(20, 10, 5, "Dual");
}
//and so on..
}
And use it like this for example:
Bicycle[] bicycles = new Bicycle[5];
bicycle[0] = createBicycle("Bicycle");

Nightmare Class - floats/strings

This is my class reponsible for new item entries, and from the start it has been a complete nightmare, I can't seem to resolve the issues I am facing which are:
setStock(float) in Item cannot be applied to ()
Item entry:
private void writeItemRecord()
{
// Check to see if we can connect to database table
if ( DataBaseHandler.makeConnectionToitemDB() == -1)
{
JOptionPane.showMessageDialog (frame, "Unable to connect to database table (Item)");
}
else // Ok, so first read data from the text fields
{
// Read data from form and store data
String Itemname = ItemnameTxtField.getText();
String Itemcode = ItemcodeTxtField.getText();
String Description = DescriptionTxtField.getText();
String Unitprice = UnitpriceTxtField.getText();
String Style = StyleTxtField.getText();
String Finish = FinishTxtField.getText();
String Stock = StockTxtField.getText();
// Convert priceStr to a float
Float fvar = Float.valueOf(Unitprice);
float price = fvar.floatValue();
Float svar = Float.valueOf(Stock);
float stock = svar.floatValue();
// Create a Item oject
Item Item = new Item();
// Set the attributes for the Item object
Item.setItemname (Itemname);
Item.setItemcode (Itemcode);
Item.setDescription (Description);
Item.setUnitprice (price);
Item.setStock(stock);
Item.setStyle(Style);
Item.setFinish(Finish);
// Write Item record. Method writeToItemTable() returns
// 0 of OK writing record, -1 if there is a problem. I store
// the returned value in a variable called error.
int error = DataBaseHandler.writeToItemTable(Item.getItemname(),
Item.getItemcode(),
Item.getDescription(),
Item.getUnitprice(),
Item.setStock(),
Item.setStyle(Style),
Item.setFinish(Finish),
Item.setSuppliercode(Suppliercode),
Item.setSuppliername(Suppliername),
Item.setAddress(Address)
);
// Check if there is a problem writing the record, in
// which case error will contain -1
if (error == -1)
{
JOptionPane.showMessageDialog (frame, "Problem writing record to Item Table");
}
// Clear the form - actual method is coded below
clearForm();
// Close database connection. Report an error message
// if there is a problem.
if ( DataBaseHandler.closeConnection() == -1 )
{
JOptionPane.showMessageDialog (frame, "Problem closing data base conection");
}
}
} // End
Any help is much appreciated!
And item extracts:
public void setStock(float StockIn)
{
Stock = StockIn;
}
public float getStock()
{
return Stock;
}

For starters, adhere to Java naming conventions. Nothing except class/interface names is allowed to use CamelCase. Use lowerCamelCase. As for your "problem", you wrote
Item.setStock(),
so obviously it's giving you the error. It is also giving you the exact line number of the error, something that would obviously have helped us to diagnose your problem.
Solution: use Item.getStock() (i suppose, it's hard to tell). Calling Item.setStock at that position (as an argument to a method call) is meaningless anyway, given that setStock is a void method.

Java compiler errors come with a line number - pay attention to it. This is your problem:
Item.setStock()
setStock() requires a parameter, you are trying to call it without one. Perhaps you meant getStock()? And I suspect that all the calls to set methods in the parameter list to writeToItemTable are also wrong, as those set methods will have void as return value, so you can't use them that way.

The setStock method looks like this:
public void setStock(float StockIn)
To call it, you need to pass a float as an argument. Somewhere in your code, you call the method, like this:
Item.setStock(),
The method needs to be called with the float argument, but instead it's called with none, hence you see a compilation error.

In this code:
int error = DataBaseHandler.writeToItemTable(Item.getItemname(),
Item.getItemcode(),
Item.getDescription(),
Item.getUnitprice(),
// Right here --> Item.setStock(),
Item.setStyle(Style),
Item.setFinish(Finish),
Item.setSuppliercode(Suppliercode),
Item.setSuppliername(Suppliername),
Item.setAddress(Address)
);
Notice that you're calling Item.setStock(), Item.setStyle(Style), etc. instead of Item.getStock(), Item.getStyle(), etc. This is probably the source of your problem - you're trying to call the setStock() method with no arguments, hence the error.
Hope this helps!

This line
// Create a Item oject
Item Item = new Item();
Is problematic. Not only is it bad style in Java to use uppercase names for variables, this particular instance results in a compile error. Also, you're calling setStock without a parameter. You need to fix that as well.

Here is your error:
int error = DataBaseHandler.writeToItemTable(Item.getItemname(),
Item.getItemcode(),
Item.getDescription(),
Item.getUnitprice(),
Item.setStock(), // <<< here! should be getStock()
Item.setStyle(Style),
Item.setFinish(Finish),
Item.setSuppliercode(Suppliercode),
Item.setSuppliername(Suppliername),
Item.setAddress(Address));
But again... consider naming/coding conventions.