Develop Reference

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);
});
}

Get and sets in Java (Newbie programmer here)

I'm trying to create a guitar program. I have a guitar amp class that has a sound object I'm trying to access in my pickup class. My goal is to set the sound property in my pickup class the same as my sound property in the GuitarAmp class so I can then set all the sound properties of my strings. I'm not really sure how to go about doing this and the articles I've read about gets and sets in Java have been no help. I have my two classes listed below, any help with the get and set would be appreciated.
public class GuitarAmp
{
// This is what I want to get from this class
public GuitarAmpSound sound;
public GuitarAmp(GuitarAmpSound sound, int volume, int distortSetting) {
sound = new GuitarAmpSound();
sound.setVolume(64);
sound.setDistortSetting(GuitarAmpSound.JAZZ);
}
public void changeVolume(int newVolume)
{
sound.setVolume(newVolume);
}
}
Here is the pickup class.
public class GuitarPickup {
public GuitarAmpSound pickupSound;
public void Connect(GuitarString strings[], GuitarAmp amp)
{
pickupSound = new GuitarAmpSound();
//This is where I need to set it
for(int i = 1; i <= 6; i++)
{
strings[i].setSound(pickupSound);
}
}
}

You need to declare a field (a variable belonging to a particular instance of a class) to hold each piece of information for that object. The pickupSound field on GuitarPickup is an example.
It is strong convention in Java to use the same name for the field as for the getters and setters. In the case of your volume, for example, the relevant part of the code would look like this:
public class GuitarAmpSound {
private int sound = 0;
public void setSound(int sound) {
this.sound = sound; // "this.sound" means the sound field, not the parameter
}
public int getSound() {
return sound; // or this.sound
}
}
If you want to implement the necessary code for your for loop, your GuitarString class needs a GuitarAmpSound field of its own named sound and a corresponding getter and setter.
As a note, the conditions in your for loop have a number of problems. Arrays in Java are zero-based (so the strings on a 6-string guitar would go from 0 to 5), and you should never hard-code array sizes in a loop but should use strings.length instead. Finally, Java has a more convenient syntax if you just want to retrieve each element in an array (or collection):
for(GuitarString string : strings) {
string.setSound(pickupSound);
}

Your code makes no sense, replace the GuitarAmp class by this:
public class GuitarAmp {
//This is what I want to get from this class
private GuitarAmpSound sound;
public GuitarAmp() {
sound = new GuitarAmpSound();
sound.setVolume(64);
sound.setDistortSetting(GuitarAmpSound.JAZZ);
}
public void changeVolume(int newVolume){
sound.setVolume(newVolume);
}
public GuitarAmpSound getSound() {
return sound;
}
public void setSound(Sound sound) {
this.sound = sound;
}
}
for get and set the rule is simple:
public YourClassName getYourObjectName() {
return yourObjectName;
}
public void setYourObjectName(YourClassName yourObjectName) {
this.yourObjectName = yourObjectName;
}

it's really complicated understand what you really wanna..take a look some change..but
I think you need to reestructure the objects. what you wanna do? can you explain better?
public class GuitarAmp {
//This is what I want to get from this class
public GuitarAmpSound sound;
--> the sound you pass before call the constructor
sound.setVoolume(x);
sound.setDistortSetting(Y)
so you pass the object sound with the attributes full of information
public GuitarAmp(GuitarAmpSound sound){
this.sound = sound;
}
public void changeVolume(int newVolume){
this.sound.setVolume(newVolume);
}
}
Here is the pickup class.
public class GuitarPickup {
public GuitarAmpSound pickupSound;
public void Connect(GuitarString strings[], GuitarAmp amp)
{
pickupSound = new GuitarAmpSound();
//This is where I need to set it
for(int i = 0; i<strings.length; i++)
{
amp.setSound(strings[i].getSound());
}
}
}

Conceptually, there is little point in saving the same Sound value to each GuitarString.

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

methods from one class to ArrayList in another class

I have a Register class contains 8 sets& gets methods
using:
public class Register {
public Register(String Username) {
JFrame myFrame = new JFrame();
}
public void setUname() {
JoptionPane.showInputDialog(myFrame, "Enter Username");
}
public String getUname() {
return Uname;
}
}
There are other methods, 8 in total all requiring user input as String or double.
How in another class, can I import the methods into an ArrayList?
public class RegisterApp {
public addUser() {
ArrayList<Register> MyReg = new Arraylist<Register>();
myReg.add(Class Register);
}
}
Uncertain really of what goes after myReg.add

You need to add a reference to a Register.
public class RegisterApp {
public addUser() {
ArrayList<Register> MyReg = new Arraylist<Register>();
//Make an instance of Register and add it to the list
myReg.add(new Register("Me"));
}
}
You also mention adding methods to the list. What do you mean by that? What else are you trying to do? Do you want to call those methods on the instances in the list? You can do that like this:
for (Register reg : myReg) {
System.out.println(reg.getUname());
}
Note:
Your set method doesn't actually save the value anywhere. You are not storing the result in uname (which should be lowecase u). In general, setters are written so they are passed the new value in. This way you are not tied to using an input dialog anytime you change the name. That is a UI decision and should not effect the data model.
public void setUname(String uname) {
this.usname = uname;
}

How to add addGlobalEventListener in a class in blackberry?

I have made a multiple entry-point project, where App2 is set to autorun and App1 runs on user request.
I am trying to invoke a global event from App1, received by App2.
public class App2 implements GlobalEventListener {
static public int counter = 0;
public static final long countId = 0x1251402f595f81a5L;
public static final long eventId = 0xba4b84944bb7429eL;
private App2() {
Application.getApplication().addGlobalEventListener(this);
}
public static App2 waitForSingleton() {
counter = 2; // Added the counter in Runtime store in a similar way as
// added in eventOccured method
// Deleted some unuseful code
}
public void eventOccurred(long guid, int data0, int data1, Object object0,
Object object1) {
if (guid == eventId) {
callMethodOnOccuranceOfEvent();
}
}
public void callMethodOnOccuranceOfEvent() {
counter++;
RuntimeStore store = RuntimeStore.getRuntimeStore();
Object obj = store.get(countId);
if (obj == null) {
store.put(countId, new Integer(counter));
} else {
store.put(countId, new Integer(counter));
}
}
}
Then in other class I tried like
public class App1 extends MainScreen {
public App1() {
}
protected void makeMenu(Menu menu, int instance) {
super.makeMenu(menu, instance);
menu.add(new MenuItem("Call", 20, 10) {
public void run() {
callMethodonclick();
}
});
}
public void callMethodonclick() {
ApplicationManager.getApplicationManager().postGlobalEvent(App2.eventId);
RuntimeStore store = RuntimeStore.getRuntimeStore();
Integer c = (Integer) store.get(App2.countId);
add(new RichTextField("Event Recived#counter#" + c));
}
}
If I invoke the event for three times
Event Recived#counter#2
Event Recived#counter#2
Event Recived#counter#2
while the Expected result is
Event Recived#counter#3
Event Recived#counter#4
Event Recived#counter#5
which I guess suggests that object for App2 in not null but eventOccurred never invoked.
the output clearly suggests that callMethodonclick is not able to post Global event,even though globalEventListener was added in constructor.

Must be like this.
if (obj == null) {
store.put(countId, new Integer(counter));
} else {
store.replace(countId, new Integer(counter));
}
store.put() throw an IllegalArgumentException, because there is something in a store(see API Reference), but this Exception is handled by some system thread, that invokes eventOccured() method and show nothing about this Exception. It is one of the various Blackberry bug.

You are not updating the text in the RichTextField. It only gets added to the screen when there is no runtimestorage object associated with App2.RTSID_MY_APP.
Your code needs to keep a handle on the RichTextField by putting it into a field of the App1 object. Then update the text in the run() method.
I edited your code, adding braces to the if statement, which makes this more clear.