Develop Reference

A way of accessing Windows MMDevice API from Java?

I would like to use the MMDevice API from my Java app. What are my options?
I tried to use JNA. Looks like I can't use JNA Typelib parsing because there no types for this API (Is there a COM type library for Windows Core Audio). As suggested, I need to provide my own declarations of the API.
So I also tried both JNA examples with manual declarations but they give "Interface not supported HRESULT=80004002" error:
public class MMDeviceAPITest {
public static void test1() {
try {
Ole32.INSTANCE.CoInitializeEx(Pointer.NULL, Ole32.COINIT_MULTITHREADED);
var obj = new Test1.MMDeviceEnumerator(); // exception E_NOINTERFACE (HRESULT: 80004002)
// ...
} finally {
Ole32.INSTANCE.CoUninitialize();
}
}
public static void test2() {
try {
Ole32.INSTANCE.CoInitializeEx(Pointer.NULL, Ole32.COINIT_MULTITHREADED);
var factory = new Factory();
var obj = factory.createObject(Test2.MMDeviceEnumerator.class); // exception E_NOINTERFACE (HRESULT: 80004002)
var in = obj.queryInterface(Test2.IMMDeviceEnumerator.class);
// ...
} finally {
Ole32.INSTANCE.CoUninitialize();
}
}
}
interface Test1 {
class MMDeviceEnumerator extends COMLateBindingObject {
public MMDeviceEnumerator() {
super(new Guid.CLSID("bcde0395-e52f-467c-8e3d-c4579291692e"), true);
}
}
}
interface Test2 {
#ComObject(clsId = "bcde0395-e52f-467c-8e3d-c4579291692e")
interface MMDeviceEnumerator extends IUnknown {} // doesn't extend IUnknown in C sources, probably it's the problem...
#ComInterface(iid = "a95664d2-9614-4f35-a746-de8db63617e6")
interface IMMDeviceEnumerator extends IUnknown {}
}
Any ideas how I could access this API from Java? Can I somehow create working declarations for JNA? Or use another framework maybe?
My last idea is to create/find a micro native app/library that wraps the needed COM calls, so I could call this app/library easily (via subprocesses or simple JNA declarations). I'm new to COM world, but it sounds working for me...

The docs you linked show how to create using CoCreateInstance:
const CLSID CLSID_MMDeviceEnumerator = __uuidof(MMDeviceEnumerator);
const IID IID_IMMDeviceEnumerator = __uuidof(IMMDeviceEnumerator);
hr = CoCreateInstance(
CLSID_MMDeviceEnumerator, NULL,
CLSCTX_ALL, IID_IMMDeviceEnumerator,
(void**)&pEnumerator);
This should get you somewhere close with JNA.
class MMDeviceEnumerator extends Unknown {
public static final CLSID CLSID_MMDeviceEnumerator = new CLSID("bcde0395-e52f-467c-8e3d-c4579291692e");
public static final GUID IID_IMMDeviceEnumerator = new GUID("a95664d2-9614-4f35-a746-de8db63617e6");
public MMDeviceEnumerator(Pointer p) {
super(p);
}
public static MMDeviceEnumerator create() {
PointerByReference pEnumerator = new PointerByReference();
HRESULT hres = Ole32.INSTANCE.CoCreateInstance(
CLSID_MMDeviceEnumerator, null,
WTypes.CLSCTX_ALL, IID_IMMDeviceEnumerator,
pEnumerator);
if (COMUtils.FAILED(hres)) {
return null;
}
return new MMDeviceEnumerator(pEnumerator.getValue());
}
// map functions as needed
}
I used the implementation of IWbemContext in JNA as a template above. You can consult that class for example COM function mappings.

For some reason I can't suggest edits to the answer of Daniel Widdis. The answer worked for me, many thanks! Just wanted to show how to map one method as an example:
class MMDeviceEnumerator extends Unknown {
public static final CLSID CLSID_MMDeviceEnumerator = new CLSID("bcde0395-e52f-467c-8e3d-c4579291692e");
public static final GUID IID_IMMDeviceEnumerator = new GUID("a95664d2-9614-4f35-a746-de8db63617e6");
public MMDeviceEnumerator(Pointer p) {
super(p);
}
public static MMDeviceEnumerator create() {
PointerByReference pEnumerator = new PointerByReference();
HRESULT hres = Ole32.INSTANCE.CoCreateInstance(
CLSID_MMDeviceEnumerator, null,
WTypes.CLSCTX_ALL, IID_IMMDeviceEnumerator, pEnumerator);
if (COMUtils.FAILED(hres)) {
return null;
}
return new MMDeviceEnumerator(pEnumerator.getValue());
}
public static final int EDataFlow_eRender = 0;
public static final int EDataFlow_eCapture = 1;
public static final int EDataFlow_eAll = 2;
public static final int EDataFlow_enum_count = 3;
public static final int DEVICE_STATE_ACTIVE = 0x1;
public static final int DEVICE_STATE_DISABLED = 0x2;
public static final int DEVICE_STATE_NOTPRESENT = 0x4;
public static final int DEVICE_STATE_UNPLUGGED = 0x8;
public static final int DEVICE_STATEMASK_ALL = 0xF;
public void EnumAudioEndpoints(int dataFlow, int dwStateMask, PointerByReference ppDevices) {
WinNT.HRESULT res = (WinNT.HRESULT) _invokeNativeObject(
3, // `EnumAudioEndpoints` is the 3rd method of `IMMDeviceEnumeratorVtbl` in `mmdeviceapi.h`
new Object[] { getPointer(), dataFlow, new WinDef.DWORD(dwStateMask), ppDevices},
WinNT.HRESULT.class
);
COMUtils.checkRC(res);
}
// map other functions as needed
}

Can't create a Object

I have an app with multiple classes:
MenuActivity, MenuThread, MenuView, MenuBot, MenuBall.
In the class "MenuView" I declare all the ib objects I need:
this.ball = new MenuBall(this, bot1);
this.bot1 = new MenuBot1(this, ball);
this.thread = new MenuThread(this,bot1,ball);
As you can see i didn't create yet the object bot1 but i already use it as a parameter in the object ball, which gives me the error.
Thank you for trying to help me !

You have to change (or add other) constructors of MenuBall and MenuBot1.
Thus, for example:
public class MenuBall {
private MenuBot1 menuBot1;
(...)
// this constructor doesn't need a MenuBot1 object.
public MenuBall(MenuView menuView) {
(...)
}
// setter for the menuBot1
public void setMenuBot1(MenuBot1 menuBot1) {
this.menuBot1 = menuBot1;
}
(...)
}
public class MenuBot1 {
private MenuBall menuBall;
(...)
// this constructor doesn't need a MenuBall object.
public MenuBot1(MenuView menuView) {
(...)
}
// setter for the menuBall
public void setMenuBall(MenuBall menuBall) {
this.menuBall = menuBall;
}
(...)
}
Then in MenuView class:
ball = new MenuBall(this);
bot1 = new MenuBot1(this);
ball.setMenuBot1(bot1);
bot1.setMenuBall(ball);
thread = new MenuThread(this, bot1, ball);
(...)

Java8 - "effectively final"

I'm using RxVertx which is a sort of RxJava along with Java8 and I have a compilation error.
Here is my code:
public rx.Observable<Game> findGame(long templateId, GameModelType game_model, GameStateType state) {
return context.findGame(templateId, state)
.flatMap(new Func1<RxMessage<byte[]>, rx.Observable<Game>>() {
#Override
public Observable<Game> call(RxMessage<byte[]> gameRawReply) {
Game game = null;
switch(game_model) {
case SINGLE: {
ebs.subscribe(new Action1<RxMessage<byte[]>>() {
#Override
public void call(RxMessage<byte[]> t1) {
if(!singleGame.contains(0) {
game = new Game(); // ERROR is at this line
singleGames.put(0, game);
} else {
game = singleGames.get(0); // ERROR is at this line
}
}
});
}
}
return rx.Observable.from(game);
}
});
}
The compilation error is:
"Local variable game defined in an enclosing scope must be final or effectively final"
I cannot define 'game' as final since I do allocation\set and return it at the end of the function.
How can I make this code compile??
Thanks.

I have a Holder class that I use for situations like this.
/**
* Make a final one of these to hold non-final things in.
*
* #param <T>
*/
public class Holder<T> {
private T held = null;
public Holder() {
}
public Holder(T it) {
held = it;
}
public void hold(T it) {
held = it;
}
public T held() {
return held;
}
public boolean isEmpty() {
return held == null;
}
#Override
public String toString() {
return String.valueOf(held);
}
}
You can then do stuff like:
final Holder<Game> theGame = new Holder<>();
...
theGame.hold(myGame);
...
{
// Access the game through the `final Holder`
theGame.held() ....

Since you need to not modify the reference of the object you can wrap the Game in something else.
The quickest (but ugly) fix is to use an array of size 1, then set the content of the array later. This works because the the array is effectively final, what is contained in the array doesn't have to be.
#Override
public Observable<Game> call(RxMessage<byte[]> gameRawReply) {
Game[] game = new Game[1];
switch(game_model) {
case SINGLE: {
ebs.subscribe(new Action1<RxMessage<byte[]>>() {
#Override
public void call(RxMessage<byte[]> t1) {
if(!singleGame.contains(0) {
game[0] = new Game();
singleGames.put(0, game[0]);
} else {
game[0] = singleGames.get(0);
}
}
});
}
}
return rx.Observable.from(game[0]);
}
Another similar option is to make a new class that has a Game field and you then set that field later.

Cyclops has Mutable, and LazyImmutable objects for handling this use case. Mutable is fully mutable, and LazyImmutable is set once.
Mutable<Game> game = Mutable.of(null);
public void call(RxMessage<byte[]> t1) {
if(!singleGame.contains(0) {
game.mutate(g -> new Game());
singleGames.put(0, game.get());
} else {
game[0] = game.mutate(g->singleGames.get(0));
}
}
LazyImmutable can be used to set a value, lazily, once :
LazyImmutable<Game> game = LazyImmutable.def();
public void call(RxMessage<byte[]> t1) {
//new Game() is only ever called once
Game g = game.computeIfAbsent(()->new Game());
}

You cant. At least not directly. U can use a wrapper class however: just define a class "GameContainer" with game as its property and foward a final reference to this container instead.

#dkatzel's suggestion is a good one, but there's another option: extract everything about retrieving/creating the Game into a helper method, and then declare final Game game = getOrCreateGame();. I think that's cleaner than the final array approach, though the final array approach will certainly work.

Although the other approaches look acceptable, I'd like to mention that you can't be sure subscribing to ebs will be synchronous and you may end up always returning null from the inner function. Since you depend on another Observable, you could just simply compose it through:
public rx.Observable<Game> findGame(
long templateId,
GameModelType game_model,
GameStateType state) {
return context.findGame(templateId, state)
.flatMap(gameRawReply -> {
switch(game_model) {
case SINGLE: {
return ebs.map(t1 -> {
Game game;
if (!singleGame.contains(0) {
game = new Game();
singleGames.put(0, game);
} else {
game = singleGames.get(0);
}
return game;
});
}
}
return rx.Observable.just(null);
});
}

Creating two objects of a class in another class in Java

I'm trying to create two objects of a Silo class in a SiloManager class, so that I can access both objects' methods. But I can't seem to make the SiloManager constructor work, nor to instance the classes properly. (I'm a beginner in java). Here's my code:
public class GrainSiloManager {
public GrainSilo silo1 = new GrainSilo(100);
public GrainSilo silo2 = new GrainSilo(50);
public GrainSiloManager(GrainSilo silo1, GrainSilo silo2) {
this.silo1 = silo1;
this.silo2 = silo2;
}
private void showStatus() {
System.out.println("The current grain in silo1 is: " + silo1.getGrain());
System.out.println("The current grain in silo2 is: " + silo2.getGrain());
}
}
As I say i'm a beginnger so go easy heh, thanks for any help.

public GrainSilo silo1 = new GrainSilo(100);
public GrainSilo silo2 = new GrainSilo(50);
public GrainSiloManager(GrainSilo silo1, GrainSilo silo2) {
this.silo1 = silo1;
this.silo2 = silo2;
}
This will get compiled as:
public GrainSilo silo1;
public GrainSilo silo2;
public GrainSiloManager(GrainSilo silo1, GrainSilo silo2) {
this.silo1 = new GrainSilo(100);
this.silo2 = new GrainSilo(50);
this.silo1 = silo1;
this.silo2 = silo2;
}
which as you can see makes little to no sense. You're overwriting the object that you make, with the objects passed into the constructor.

Your constructor is going to replace the "public!" silo1 and silo2 objects with whatever is passed in. You could change your constructor like this
public GrainSiloManager() {
super();
}
or the even shorter (but equivalent)
public GrainSiloManager() {
}
And then call it like this
new GrainSiloManager().showStatus();
or you can use your existing approach (which will replace the GrainSoloManager.silo1 and GrainSoloManager.silo2 in your constructor)
GrainSilo silo1 = new GrainSilo(100);
GrainSilo silo2 = new GrainSilo(50);
new GrainSiloManager(silo1, silo2).showStatus();

Java access a public variable outside a class, SecurityException: MIDlet not constructed by createMIDlet

I'm a newbie in java and I have a small problem. I want to access a variable in one class from another. I have three classes and I want to be able to access a variable in the main class to enable me read the array.
The error I am getting is
java.lang.SecurityException: MIDlet not constructed by createMIDlet
Please see the example below. Please bear in mind they're all in the same package.
package tungPackage;
import com.sun.lwuit.*;
import com.sun.lwuit.animations.CommonTransitions;
import com.sun.lwuit.events.ActionEvent;
import com.sun.lwuit.events.ActionListener;
import javax.microedition.midlet.MIDlet;
public class TungMidlet extends MIDlet implements ActionListener {
private Command back = new Command("Back");
private Command ok = new Command("Ok");
public ActionListener commandlistListener = new ActionListener() {
public void actionPerformed(ActionEvent cmd) {
// check which command cliked
if (cmd.getCommand() == back) {
// go back to previous form
mainForm.show();
} else if (cmd.getCommand() == ok) {
// go forward
}
}
};
private List list;
private Form mainForm;
private Label promptLabel;
private housesClass houseClassObject = new housesClass();
public int counter; //this is the variable I want to access in a class called calculate class object.
private int sumAmmt;
public TungMidlet tungMidletObject;
public calculateClass calculateClassObject;
public TungMidlet() {
Display.init(this);
}
private ActionListener applistListener = new ActionListener() {
public void actionPerformed(ActionEvent ae) {
if(list.getSelectedIndex()==0){
counter++;
if (counter>5)
{
//check sum price.
sumAmmt = calculateClassObject.calculateSum();
Dialog x = new Dialog("info");
Label label = new Label("Maximum reached.");
Label label2 = new Label("Sum ammt = "+sumAmmt);
x.addComponent(label);
x.addComponent(label2);
x.addCommand(ok);
x.show();
}
else
{
//calculate the price
String info = houseClassObject.randomHouse();
Dialog x = new Dialog("info");
Label label = new Label(info);
x.addComponent(label);
x.addCommand(ok);
x.show();
}
}
}
};
public void startApp() {
//calculateClassObject = new calculateClass();
//sumAmmt = calculateClassObject.calculate(sumAmmt);
mainForm = new Form("Investment Categories");
promptLabel = new Label("choose category");
list = new List();
list.addItem("House");
list.addItem("Cars");
list.addItem("Schools");
list.addItem("Schools");
list.addItem("Supermarkets");
list.addItem("Stocks");
list.addItem("Land");
list.addActionListener(applistListener);
mainForm.addComponent(promptLabel);
mainForm.addComponent(list);
mainForm.addCommand(back);
mainForm.addCommandListener(commandlistListener);
mainForm.setTransitionInAnimator(CommonTransitions.createSlide(CommonTransitions.SLIDE_HORIZONTAL, true, 1000));
mainForm.show();
}
public void pauseApp() {}
public void destroyApp(boolean unconditional) {}
public void actionPerformed(ActionEvent ae) {
throw new UnsupportedOperationException("Not supported yet.");
}
}
The class I want to access the "counter" variable using is shown below.
package tungPackage;
import java.util.Random;
public class housesClass {
public Random generator = new Random();
public String[] houseArray = new String[5];
public housesClass housesClassObject;
public calculateClass calcobj;// = new calculateClass();
public housesClass()
{
}
public String randomHouse() {
housesClassObject = new housesClass();
houseArray[0] = "Bungalow - 20,000,000 Shillings";
houseArray[1] = "Microhouse - 10,000,000 Shillings";
houseArray[2] = "Flat - 200,000,000 shillings";
houseArray[3] = "Garage apartment - 7,000,000 shillings";
houseArray[4] = "Studio apartment - 13,000,000 shillings";
int rnd = generator.nextInt(houseArray.length);
housesClassObject.housePrices(rnd);///noma
String house = houseArray[rnd];
return house;
}
void housePrices(int houseNumber) {
calcobj = new calculateClass();
TungMidlet tungmidobj = new TungMidlet();
int counter = tungmidobj.counter;
int[] housePriceArray = new int[5];
housePriceArray[0] = 20000000;
housePriceArray[1] = 10000000;
housePriceArray[2] = 200000000;
housePriceArray[3] = 7000000;
housePriceArray[4] = 13000000;
int price = housePriceArray[houseNumber];
calcobj.storePrice(counter,price);
}
}
The other supporting class is shown below.
package tungPackage;
public class calculateClass {
int[] storeArray = new int[5];
public calculateClass()
{
}
public void storePrice(int counter, int number2)
{
storeArray[counter] = number2;
}
public int calculateSum()
{
int sum =0;
for(int i=1; i<6; i++){
sum= sum+storeArray[i];
}
return sum;
}
}

Are you getting an error? It looks like your access code should work.
I can't seem to find anywhere that you actually initialise counter though, so maybe your problem is that you need to put counter = 0; somewhere in your code.
Java is also object oriented so you should avoid accessing like the above and make some 'getter and setter' methods:
public int getCounter() {
return counter;
}
and then call int counter = tungmidobj.getCounter();

remove TungMidlet constructor. If there was something useful to do there, you could also declare it protected - but this is not the case with your code snippet, see below.
Wherever you try to invoke that constructor directly, remove code that does this and find another way to do what you need. If needed, study code examples provided in LWUIT Tutorial - Introduction for how typical things are done in LWUIT.
put statement Display.init() in the beginning of the startApp method,
just like it is done in LWUIT Tutorial - Hello, LWUIT! example code
The reason why you are getting SecurityException is because you invoke TungMidlet constructor directly. Don't do that.
MIDP API documentation for MIDlet constructor states:
Throws:
SecurityException - unless the application management software is creating the MIDlet.

one way is
TungMidlet tungMidlet=new TungMidlet();
System.out.println(tungMidlet.counter);
but know encapsulation
second way is
you can make counter private variable and provide setter and getters.
private int counter;
public void setCounter(int counter){
this.counter=counter;
}
public int getCounter(){
return counter;
}
second way is preferred way as it achieves encapsulation