We Keep Coding

java print arraylist of interface

I'm learning observer design pattern from one of youtube videos and want to understand a bit more the behavior of interface arraylist, I think I quite understand how it works but when it comes the interface arraylist, its confusing to me how to access the value inside loop.
the subject and observer interfaces as follow;
public interface Subject {
public void register(Observer o);
public void unregister(Observer o);
public void notifyObserver();
}
public interface Observer {
public void updateViaObserver(double ibmPrice, double aaplPrice, double googPrice);
}
package observer_pattern;
import java.util.ArrayList;
import java.util.Arrays;
public class StockGrabber implements Subject{
private ArrayList<Observer> observers;
private double ibmPrice;
private double aaplPrice;
private double googPrice;
public StockGrabber(){
// Creates an ArrayList to hold all observers
observers = new ArrayList<Observer>();
}
public void register(Observer newObserver) {
observers.add(newObserver);
}
public void notifyObserver() {
for(Observer observer : observers){
observer.updateViaObserver(ibmPrice, aaplPrice, googPrice);
}
}
public void setPrice(double newIBMPrice, double newAAPLPrice, double newGOOGPrice){
this.ibmPrice = newIBMPrice;
this.aaplPrice = newAAPLPrice;
this.googPrice = newGOOGPrice;
notifyObserver();
}
}
package observer_pattern;
public class StockObserver implements Observer {
private double ibmPrice;
private double aaplPrice;
private double googPrice;
private Subject stockGrabber;
public StockObserver(Subject stockGrabber){
this.stockGrabber = stockGrabber;
this.observerID = ++observerIDTracker;
stockGrabber.register(this);
}
// Called to update all observers
public void updateViaObserver(double ibmPrice, double aaplPrice, double googPrice) {
this.ibmPrice = ibmPrice;
this.aaplPrice = aaplPrice;
this.googPrice = googPrice;
// this works
printThePrices();
// doesn't work
toString();
}
public void printThePrices(){
System.out.println(observerID + "\nIBM: " + ibmPrice + "\nAAPL: " +
aaplPrice + "\nGOOG: " + googPrice + "\n");
}
public String toString() {
return "StockObserver: ibmPrice=" + ibmPrice + " aaplPrice=" + aaplPrice;
}
}
MAIN
package observer_pattern;
public class GrabStocks{
public static void main(String[] args){
StockGrabber stockGrabber = new StockGrabber();
StockObserver observer1 = new StockObserver(stockGrabber);
stockGrabber.setIBMPrice(197.00);
stockGrabber.setAAPLPrice(677.60);
stockGrabber.setGOOGPrice(676.40);
observer1.toString();
}
}
How to access value for my ArrayList<Observer> observers inside "notifyObserver" method? if I do this System.out.println(observers.get(0)); I get observer_pattern.StockObserver#446cdf90

How to access value for my ArrayList observers inside "notifyObserver" method?
You're already doing it.
public void notifyObserver() {
for(Observer observer : observers){
observer.updateViaObserver(ibmPrice, aaplPrice, googPrice);
}
}
if I do this System.out.println(observers.get(0)); I get observer_pattern.StockObserver#446cdf90
That's because your StockObserver class does not have a toString method that returns a human readable representation of the object. Something like this
public String toString() {
return "StockObserver: ibmPrice=" + ibmPrice + " aaplPrice=" + aaplPrice;
}

Selecting Random Method From Multiple Methods

I am trying to select a random method from the ones created inside the class. Is there a way to create an ArrayList and pass methods to it? I have attempted to do just that but I am getting an error when I try to add the method to the array.
public class Monkey{
private int energy;
String[] food = {"Meat", "Fish", "Bugs", "Grain"};
ArrayList<Activity> monkeyActivity = new ArrayList<>();
public Monkey(int energy) {
this.energy = energy;
}
public int getEnergy() {
System.out.println("Monkey energy level: " + energy);
return energy;
}
public void sound() {
System.out.println("Monkey: Oooo Oooo~!");
energy -= 3;
monkeyActivity.add(sound()); //I get an error message here when trying
//to add the method to the array
}
public void play(){
if (energy >= 8){
System.out.println("Monkey begins to play.");
energy -= 8;
}else {
System.out.println("Monkey does not have enough energy to play");
}
System.out.println("Energy remaining: " + energy);
}
public void eat(){
Random random = new Random();
int index = random.nextInt(food.length);
System.out.println("Monkey beings to eat " + food[index]);
energy += 5;
System.out.println("Energy remaining: " + energy);
}
public void sleep(){
System.out.println("Monkey is sleeping: Zzz...");
energy += 10;
System.out.println("Energy remaining: " + energy);
}
}
This is the separate class I have made for the generic Activity..
public class Activity {
private String sleep;
private String eat;
private String sound;
private String play;
public Activity(String sleep, String eat, String sound, String play) {
this.sleep = sleep;
this.eat = eat;
this.sound = sound;
this.play = play;
}
public String getSleep() {
return sleep;
}
public String getEat() {
return eat;
}
public String getSound() {
return sound;
}
public String getPlay() {
return play;
}
public void setSleep(String sleep) {
this.sleep = sleep;
}
public void setEat(String eat) {
this.eat = eat;
}
public void setSound(String sound) {
this.sound = sound;
}
public void setPlay(String play) {
this.play = play;
}
}

You are mixing up concepts.
technical issues:
return value clash
public void sound() {
// ...
monkeyActivity.add(sound());
The return value of your method sound() is void (which means no return value), but you try to add its (not existing) return value as element to the List. This is what your compiler complains about.
unintended recursion
public void sound() {
System.out.println("Monkey: Oooo Oooo~!");
energy -= 3;
monkeyActivity.add(sound());
In the last line you do a recursive call which means you call exactly the same method this code is in. If that happens unintended it almost ever results in a StackOverflowError.
writing classes without proper analysis
You have a class Activity.
But if you have a closer look this is not a single activity (as the classes name implies) but it is all possible activities.
As a result your collection monkeyActivity cannot hold single activities as elements.
Doing a wild guess I think what you wanted is more like this:
interface Activity{
void do();
}
public class Monkey{
private int energy;
String[] food = {"Meat", "Fish", "Bugs", "Grain"};
List<Activity> monkeyActivity = new ArrayList<>();
// ...
public void sound() {
monkeyActivity.add(new Activity(){
public void do(){
System.out.println("Monkey: Oooo Oooo~!");
energy -= 3;
}
});
}

You may store each method as Runnable, as any "action" is no-arg void method satisfying Runnable functional interface:
List<Runnable> actions = Arrays.asList(this::sound, this::play, this::eat, this::sleep);
to execute random method, just:
Random rnd = new Random();
actions.get(rnd.nextInt(actions.size())).run();

Player class winning percentage java

I am trying to create a method for " winning percentage " in a player class. I know I need to incorporate total wins divided by total games played, but the code is meant to be simple so I cannot use complex code. (beginner project in computer science) Any useful feedback would be great as I have spent multiple days attempting this and getting no where. By the way, ties count as half a win.
Update: Implemented the getters into the getWinningPercentage method. Also calculated everything inside the getWinningPercentage and removed the setWinningPercentage considering it was useless code. Results were as follows:
Bob
5 wins, 1 losses, 2 ties
Winning percentage = 0.75
public class Player
{
private int numWins = 0;
private int numTies = 0;
private int numLosses = 0;
private String name;
public void setWins(int w)
{
numWins = w;
}
public int getWins()
{
return numWins;
}
public void setTies(int t)
{
numTies = t;
}
public int getTies()
{
return numTies;
}
public void setLosses(int L)
{
numLosses = L;
}
public int getLosses()
{
return numLosses;
}
public void setName(String n)
{
name = n;
}
public String getName()
{
return name;
}
public void incrementWins()
}
numWins++;
}
public void incrementTies()
{
numTies++;
}
public void incrementLosses()
{
numLosses++;
}
public double getWinningPercentage()
{
double totalGames = getWins() + getTies() + getLosses();
double totalWins = getWins() + (getTies() / 2.0);
double winningPercentage = (totalWins / totalGames);
return winningPercentage;
}
}

The winning percentage should be a calculated property, not a field, and not have a setter method. Instead there should only be a "getter" (public double getWinningPercentage()) method and you should calculate and return this value from within the method itself from the other fields that your class already has.
We should leave it up to you to create this method and formula yourself.

Is it a good way to implement Distance with diffrent units

I was looking for some good patterns to have possibility to express distance in different units. I found Martin Fowler article about quantities and I programmed something like:
Here is Distance class ( I think it is not necessery to make it abstract ):
public class Distance {
double mValue;
DistanceUnit mUnit;
public Distance(double value, DistanceUnit unit){
this.mValue = value;
this.mUnit = unit;
}
public Distance toUnit(DistanceUnit unit){
double factor = this.mUnit.getMetresFactor()/unit.getMetresFactor();
double newValue = this.mValue * factor;
Distance distance = new Distance(newValue, unit);
return distance;
}
#Override
public String toString(){
return String.valueOf(mValue);
}
}
It looks very simple. Conversion toUnit is based on DistanceUnit method getMetresFactor. Each Unit class implements DistanceUnit interface and has method getMetresFactor() like:
public interface DistanceUnit {
double getMetresFactor();
}
public class Inch implements DistanceUnit {
#Override
public double getMetresFactor() {
return 0.0254;
}
}
public class Kilometer implements DistanceUnit {
#Override
public double getMetresFactor() {
return 1000.0;
}
}
And the usage is for example:
Distance inches = new Distance(300.0, new Inch());
Distance kilometres = inches.toUnit(new Kilometres());
So it returns the correct value.
Is it good way to store distance in this way? Maybe you know some weaknesses of this approach. Maybe is a good idea to use here a FactoryMethod pattern to construct distance based on unit shortcut like "m" for meter. I think about the amount of classes if I would have a lot of units... Is it good idea to have factory which return factor of meters based on unit name? There will be no classes for units then?

Hm, i would use enum instead of DistanceUnit classes, because there is no different instances of them.
You can set a value to enum like here
and then call enum.getValue() instead of unit.getMetresFactor().
Also it is a little bit confusing, is the mValue value in meters or in DistanceUnit's, if in meters, you must have
double factor = unit.getMetresFactor();
there
Ok and now with any convertion function support:
import java.util.HashMap;
import java.util.Map;
public abstract class MeasureConverter {
public abstract double valueToBasic(double value);
public abstract double basictoValue(double basic);
/**
*
*/
public static Map<String, MeasureConverter> converters;
public static Map<String, MeasureConverter> getConverters() {
if (converters == null) {
converters = new HashMap<String, MeasureConverter>();
converters.put("kilo", new MeasureConverter() {
#Override
public double valueToBasic(double value) {
return value * 1000;
}
#Override
public double basictoValue(double basic) {
return basic / 0.001;
}
});
// taking the basic temperature value in kelvines
converters.put("kelvine", new MeasureConverter() {
#Override
public double valueToBasic(double value) {
return value;
}
#Override
public double basictoValue(double basic) {
return basic;
}
});
converters.put("celsius", new MeasureConverter() {
#Override
public double valueToBasic(double value) {
return value + 273.15;
}
#Override
public double basictoValue(double basic) {
return basic - 273.15;
}
});
converters.put("faren", new MeasureConverter() {
#Override
public double valueToBasic(double value) {
return value * 1.8 - 459.67 ; // or whatever is there?
}
#Override
public double basictoValue(double basic) {
return (basic + 459.67 ) / 1.8;// or whatever is there?
}
});
}
return converters;
}
}
And then :
import java.util.Objects;
public class MeasurePattern {
double value;
String name;
public MeasurePattern(double value, String name) {
this.value = value;
this.name = name;
}
#Override
public String toString() {
return "MeasurePattern{" + "value=" + value + ", name=" + name + '}';
}
#Override
public int hashCode() {
int hash = 7;
hash = 29 * hash + (int) (Double.doubleToLongBits(this.value) ^ (Double.doubleToLongBits(this.value) >>> 32));
hash = 29 * hash + Objects.hashCode(this.name);
return hash;
}
#Override
public boolean equals(Object obj) {
if (obj == null) {
return false;
}
if (getClass() != obj.getClass()) {
return false;
}
final MeasurePattern other = (MeasurePattern) obj;
if (Double.doubleToLongBits(this.value) != Double.doubleToLongBits(other.value)) {
return false;
}
if (!Objects.equals(this.name, other.name)) {
return false;
}
return true;
}
public MeasurePattern convertTo(String converter) {
MeasureConverter mycon = MeasureConverter.getConverters().get(name);
MeasureConverter hiscon = MeasureConverter.getConverters().get(converter);
double basic = mycon.valueToBasic(value);
double hisValue = hiscon.basictoValue(basic);
return new MeasurePattern(hisValue, converter);
}
public static void main(String[] args) {
//trying temperatures;
MeasurePattern temp = new MeasurePattern(10, "celsius");
MeasurePattern kelvine = temp.convertTo("kelvine");
MeasurePattern faren = kelvine.convertTo("faren");
MeasurePattern cels = faren.convertTo("celsius");
System.out.println("kelvine = " + kelvine);
System.out.println("faren = " + faren);
System.out.println("cels = " + cels);
}
}
Output:
kelvine = MeasurePattern{value=283.15, name=kelvine}
faren = MeasurePattern{value=412.67777777777775, name=faren}
cels = MeasurePattern{value=9.999999999999943, name=celsius}

You can implement it analog to java.util.concurrent.TimeUnit as an enum. E.g.
public enum DistanceUnit {
KILOMETER {
#Override
protected double conversionFactor(DistanceUnit toDistanceUnit) {
switch (toDistanceUnit) {
case KILOMETER:
return 1;
case MILE:
return 0.621371;
default:
throw new UnsupportedOperationException(toDistanceUnit + " is not supported");
}
}
},
MILE {
#Override
protected double conversionFactor(DistanceUnit toDistanceUnit) {
switch (toDistanceUnit) {
case KILOMETER:
return 1.60934;
case MILE:
return 1;
default:
throw new UnsupportedOperationException(toDistanceUnit + " is not supported");
}
}
};
public double toDistance(double value, DistanceUnit targetDistance) {
return value * conversionFactor(targetDistance);
}
protected abstract double conversionFactor(DistanceUnit toDistanceUnit);
}
change your Distance class to
public class Distance {
double mValue;
DistanceUnit mUnit;
public Distance(double value, DistanceUnit unit){
this.mValue = value;
this.mUnit = unit;
}
public Distance toUnit(DistanceUnit unit){
double newValue = mUnit.toDistance(mValue, unit);
Distance distance = new Distance(newValue, unit);
return distance;
}
#Override
public String toString(){
return String.valueOf(mValue);
}
}
and the client code will look very clear
public class Main {
public static void main(String[] args) {
Distance kilometers = new Distance(265.35, DistanceUnit.KILOMETER);
Distance miles = kilometers.toUnit(DistanceUnit.MILE);
System.out.println(miles);
}
}
will output
164.88079485000003

Java convention does not use a m(ember) prefix (but say a this. qualification), and convention is taken quite seriously in java (as opposed to C++ for instance).
toString misses the unit.
JScience offers more, the capability to calculate in different units, m/s², and so on. Your class is a nice abstraction. But in a wider context, you probably will want to have math operations, powers of units (-2 for s above).
Take a look at your own usage ideas first:
(Just garbage:)
U speedUnit = U.of(Distance::km, Time::h.up(-1));
double timeInS = U.mile(40).div(speedunit(30)).in(U.m);

I think you should use the "Strategy" pattern.
An interface:
public interface DistanceUnit {
double getDistance(int metres);
}
The Inch class:
public class Inch implements DistanceUnit {
#Override
public double getDistance(int metres) {
return meters*39; //do conversion here
}
}
The Kilometers class:
public class Kilometres implements DistanceUnit {
#Override
public double getDistance(int metres) {
return meters/1000; //do conversion here
}
}
Then:
List<DistanceUnit> distanceList = new ArrayList<>();
distanceList.add(new Inch());
distanceList.add(new Kilometres());
for (DistanceUnit item : distanceList) {
System.out.println(item.getDistance(1000));
}
If I understand you, I think it is a simple and clean solution.
You can follow this model for conversion between others units.

javafx: How to monitor state change of a variable that has more than 2 states?

I have a variable money of type double. I want this variable to have 3 states like this:
double money = something;
public int getMoneyState(){
if (money > 0){
return 1;
} else if(money == 0){
return 0;
} else{
return -1;
}
}
Problem is: I only know how to formulate this problem in the most conventional way, that is without using any javafx libraries / functions.
Eventually, I want to have a tableView where one of the columns will display the money variable, and its font color will change depending on the state of this variable, i.e. if after editing the cell, money = 100, the state will be 1 and font color is yellow. If after editing the cell, money = 0, the state will be 0 and font color is grey.And if after editing the cell, money = -555, the state will be -1 and font color is Green.
What I am looking for: I want to be able to track the money variable as well as its state and any changes in state. By that, I mean a change in the money variable will lead to a change in the state by using a method similar to getMoneyState() above. And depending on the state of the variable, the cell's font color will change.
I need help re-writing getMoneyState() method such that the state will automatically be updated after the user edits the money cell.
Hope this makes more sense.

Assuming you have money represented as a DoubleProperty:
DoubleProperty money = new SimpleDoubleProperty();
for example, you can do
IntegerBinding moneyState = Bindings.createIntegerBinding(() -> {
if (money.get() > 0) {
return 1 ;
} else if (money.get() == 0) {
return 0 ;
} else {
return -1 ;
}
}, money);
The two arguments to createIntegerBinding are a function returning an Integer, and a list of other observables on which the binding depends (here there is only one, money).
Now you can add listeners to moneyState or bind to it in the usual way.
If money is a property in some bean, then you can expose moneyState as a ReadOnlyIntegerProperty in a similar way:
public class MyEntity {
private final DoubleProperty money = new SimpleDoubleProperty();
public DoubleProperty moneyProperty() {
return money ;
}
public final double getMoney() {
return moneyProperty().get();
}
public final void setMoney(double money) {
moneyProperty().set(money);
}
private final ReadOnlyIntegerWrapper moneyState = new ReadOnlyIntegerWrapper();
public ReadOnlyIntegerProperty moneyStateProperty() {
return moneyState.getReadOnlyProperty();
}
public int getMoneyState() {
return moneyStateProperty().get();
}
private IntegerBinding moneyStateBinding ;
public MyEntity(double money) {
setMoney(money) ;
moneyStateBinding = Bindings.createIntegerBinding(() -> {
if (getMoney() > 0) {
return 1 ;
} else if (getMoney() == 0) {
return 0 ;
} else {
return -1 ;
}
}, moneyProperty());
moneyState.bind(moneyStateBinding);
}
}
A couple of other options. First note that your logic is already implemented by Math.signum(), so you can do:
IntegerBinding moneyState = Bindings.createIntegerBinding(() ->
(int) Math.signum(money.get()), money);
You can also implement it with the fluent Bindings API:
IntegerBinding moneyState = Bindings.when(money.greaterThan(0)).then(1)
.otherwise(Bindings.when(money.isEqualTo(0)).then(0).otherwise(-1));

You could create and Observer and make a MoneyClass, which inherits the Observable Class for example. You could then track any changes to the Money and it´s state made
The result could be looking like this
// Money class
import java.util.Observable;
public class MoneyClass extends Observable{
private double money = 0;
private int state = 0;
public static final int POSITIV = 1;
public static final int ZERO = 0;
public static final int NEGATIV = -1;
public int getMoneyState(){
if (money > 0){
return MoneyClass.POSITIV;
} else if(money == 0){
return MoneyClass.ZERO;
} else{
return MoneyClass.NEGATIV;
}
}
public void setMoney(int money) {
this.money = money;
setChanged();
notifyObservers("Money");
setMoneyState();
}
public double getMoney() {
return money;
}
public int getState() {
return state;
}
private void setMoneyState() {
if (state != getMoneyState()) {
state = getMoneyState();
setChanged();
notifyObservers("State");
}
}
public static void main(String[] args) {
}
}
//Observer
import java.util.Observable;
import java.util.Observer;
public class MoneyObserver implements Observer{
public void addObserving(MoneyClass money) {
money.addObserver(this);
}
#Override
public void update(Observable o, Object arg) {
if(arg instanceof String) {
String type = (String) arg;
if(type.equals("Money")) {
System.out.println("Money got changed to " + ((MoneyClass)o).getMoney());
} else if(type.equals("State")) {
System.out.println("State got changed to " + ((MoneyClass)o).getState());
}
}
}
public static void main(String[] args) {
MoneyObserver o = new MoneyObserver();
MoneyClass c = new MoneyClass();
o.addObserving(c);
c.setMoney(20);
c.setMoney(50);
c.setMoney(-30);
}
}