We Keep Coding

java.util.ArrayList cannot be cast to java.lang.Comparable

I have UniversalComparator and it does all the task related to sorting, It uses reflection API to recognized the method name and invocatio target.
Now what happened is, I need to sort the sites, previously it was sorted using "name", now what happened is, user need to upload documents in frequency of monthly, quarterly,semi and annually.
REQUIREMENT
If document not uploaded in any of the frequency, that data represent with white color, rest of the blocks are reprsented as red color.
There are six SITES right now,
first site has only one white block
second site has no white block.
third site has no white block
four has three white block
fifth has three white block
sixth has three white block
so the count is
1
0
0
3
3
Now whta I did, I cretaed an ArrayList of Integer and store all the count
now I need to sort the list of SITE Block on behalf of this count so it should be like
0
0
1
3
3
CODE
package com.lear.common.utility;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.Comparator;
public class UniversalComparator implements Comparator {
/**
* static final int ASCENDING
*/
public static final int ASCENDING = 1;
/**
* static final int DESCENDING
*/
public static final int DESCENDING = -1;
/*
* int for descAscIndicator
*/
private int descAscIndicator = 1;
/*
* String to store method Name
*/
private String methodName = "toString";
/**
* Constructor for UniversalComparator
*
* #param descAscIndicator
* int to store descAscIndicator.
*/
public UniversalComparator(int descAscIndicator) {
this.descAscIndicator = descAscIndicator;
}
/**
* Constructor for UniversalComparator
*
* #param methodName
* : name of method as criteria
* #param descAscIndicator
* : order of sorting
*/
public UniversalComparator(String methodName, int descAscIndicator) {
this(descAscIndicator);
this.methodName = methodName;
}
/**
* This Method compare Two Objects
*
* #param o1
* : An Instance of Object.
* #param o2
* : An Instance of Object.
* #return int
*/
public int compare(Object o1, Object o2) {
Object comp1 = null;
Object comp2 = null;
try {
Method o1_Method = (o1.getClass()).getMethod(methodName, null);
Method o2_Method = (o2.getClass()).getMethod(methodName, null);
comp1 = o1_Method.invoke(o1, null);
comp2 = o2_Method.invoke(o2, null);
} catch (NoSuchMethodException e) {
throw new RuntimeException("Method does not exist" + e.getMessage());
} catch (IllegalAccessException e) {
throw new RuntimeException("Illegal access" + e.getMessage());
} catch (InvocationTargetException e) {
throw new RuntimeException("InvocationTargetException"
+ e.getMessage());
}
Comparable c1 = (Comparable) comp1;
Comparable c2 = (Comparable) comp2;
return c1.compareTo(c2) * descAscIndicator;
}
/**
* Check for Equality obect
*
* #param obj
* : An Instance of Object.
* #return boolean return true if equal or false if not
*/
public boolean equals(Object obj) {
return this.equals(obj);
}
}
ScoreCardManager.java
List<Integer> naSiteDataList = new ArrayList<Integer>();
public String getComparativeSiteAnalysis(Integer divId, String lang, int selectedYear) {
// PLENTY OF CODE HERE
int annualDataCount = site.getComparativeColorAnnual().equalsIgnoreCase("White") ? 1 : 0;
naSiteDataCount = monthlyDataCount + quaterlyDataCount + semiAnnualDataCount + annualDataCount;
naSiteDataList.add(naSiteDataCount);
naSiteCounter.add(naSiteDataCount);
site.setNaSiteCount(naSiteDataList);
site.setNaSiteCounter(naSiteCounter);
System.out.println("datacount is" + naSiteDataCount);
}
// THIS LINE
Collections.sort(sites, new UniversalComparator("getNaSiteCount", 1));
Site.java
public class Site{
// lot of properties
private List<Integer> naSiteCount;
public List<Integer> getNaSiteCount() {
return naSiteCount;
}
public void setNaSiteCount(List<Integer> naSiteCount) {
this.naSiteCount = naSiteCount;
}
}

Reflection is a really awful approach to this. You have absolutely no type safety in this code. You have no guarantee that a method with the name you supply as a string actually exists. You have no guarantee that it takes no arguments. You have no idea what exceptions it might throw.
If you were working in Java 8 plus, it would be trivial to implement specific comparators:
Comparator<Object> comparator = Comparator.comparing(Object::toString);
but the lack of Java 8 features isn't a reason to do it with reflection.
Define an abstract class:
abstract class AbstractComparator<T, C extends Comparable<? super C>> implements Comparator<T> {
abstract C toComparable(T object);
#Override public int compare(T a, T b) {
return toComparable(a).compareTo(toComparable(b));
}
Comparator<T> reverse() {
return new Comparator<T>() {
#Override public int compare(T a, T b) {
return toComparable(b).compareTo(toComparable(a));
}
}
}
}
and then implement this for your specific cases:
Comparator<Object> comparator = new AbstractComparator<Object, String> {
#Override String toComparable(Object object) { return object.toString(); }
}.reverse();
If you are using Guava or some other library with a Function-like class, or are happy to define it yourself, you can of course take a compositional approach, rather than using inheritance:
Comparator<Object> comparator = new ConcreteComparator<>(new Function<Object, String>() {
#Override public String apply(Object object) {
return object.toString();
}
});
Provided you don't use raw types around either the comparator or the things you are comparing, ClassCastExceptions will now be impossible.

How to change values in the SET Method

I am starting to develop my skills in JAVA, however I have a doubt.
I'm creating an object in JAVA, created the constructor and so on, then, it asks "Change the AGE_RECENT value from 1 to 3", I initially declared this as final because I never thought it would change, so no SET or GET were created. I am wondering how can I change the value from 1 to 3 in the SET Method.
I have this variable
private static int AGE_RECENT=1;
I did this.
public void setAgeRecent() {
Vehicle.AGE_RECENT = 3;
}
It works if you run the program, it changes the variable's value, however nothing was declared in that method as every SET method.
Just wondering how can I do this. If this is correct, good, if not, thanks for helping!
As someone asked, the code.
/*
* To change this license header, choose License Headers in Project Properties.
* To change this template file, choose Tools | Templates
* and open the template in the editor.
*/
package tp1;
/**
*
* #author Nelson
*/
public class Vehicle {
/** Variáveis da classe, têm como função **/
private String registration;
private int registrationYear;
private double consumption;
private double autonomy;
private int cilinderCapacity;
/**
* Final variables. They are final because they do not suffer any kind of modification during the project.
* YEAR_OMISSION is 2016 because the currect year is 2016.
* ENVIRONMENTAL_CHARGE_OMISSION is 0.10(10 cents), gave this value because there is nothing to mention the
especific value, hence why I gave 0.10.
* RATING_RECENT = Is a string, just has the text "RECENT" inside.
* RATING_COMTEMPORY - Another string, just with the "Comtempory" text inside.
* RATING_CLASSIC - Yet again another string, with the "Classic" text.
* AGE_RECENT - It is to help to compare if a vehicle is recent or not, it has the value 3.
* AGE_CLASSIC - It is to again help to compare, value is 20.
*/
private static final int YEAR_OMISSION = 2016;
private static final double ENVIRONMENTAL_CHARGE_OMISSION=0.10;
private static final String RATING_RECENT="Recent";
private static final String RATING_CONTEMPORY="Contempory";
private static final String RATING_CLASSIC="Classic";
private static int AGE_RECENT=1;
private static final int AGE_CLASSIC=20;
/**
* Constructor of the object, it has the Registration
* #param registration
* #param registrationYear - The year the vehicle was first registered.
* #param consumption - How many liters the vehicle consumes.
* #param autonomy - How many KMs a vehicle can go without refuelling.
* #param cilinderCapacity - How many Cubic Inches the engine has.
*/
public Vehicle(String registration,int registrationYear, double consumption, double autonomy, int cilinderCapacity) {
this.registration = registration;
this.registrationYear = registrationYear;
this.consumption = consumption;
this.autonomy = autonomy;
this.cilinderCapacity = cilinderCapacity;
}
/**
* Null Constructor, it has no values, they will be attributed in the MAIN Class.
*/
public Vehicle() {
this.registration = "";
this.registrationYear = 0;
this.consumption = 0;
this.autonomy = 0;
this.cilinderCapacity =0;
this.registrationYear = YEAR_OMISSION;
}
/**
* Copy Constructor.
*/
public Vehicle(Vehicle vehicle) {
this.registration = vehicle.getRegistration();
this.registrationYear = vehicle.getRegistrationYear();
this.consumption = vehicle.getConsumption();
this.autonomy = vehicle.getAutonomy();
this.cilinderCapacity = vehicle.getCilinderCapacity();
}
public String getRegistration() {
return registration;
}
public int getRegistrationYear() {
return registrationYear;
}
public double getConsumption() {
return consumption;
}
public double getAutonomy() {
return autonomy;
}
public int getCilinderCapacity() {
return cilinderCapacity;
}
public double getYearRecent() {
return AGE_RECENT;
}
public double getAgeRecent(){
return AGE_RECENT;
}
public void setRegistration(String registration) {
this.registration = registration;
}
public void setRegistrationYear(int registrationYear) {
this.registrationYear = registrationYear;
}
public void setConsumption(double consumption) {
this.consumption = consumption;
}
public void setAutonomy(double autonomy) {
this.autonomy = autonomy;
}
public void setCilinderCapacity(int cilinderCapacity) {
this.cilinderCapacity = cilinderCapacity;
}
public void setAgeRecent() {
Vehicle.AGE_RECENT = 3;
}
/**
* Calculate the age of the vehicle to compare in the vehicleRating method
* #return The year, which is 2016 minus the year the vehicle was first registered.
*/
private int calculateAge(){
return YEAR_OMISSION-this.registrationYear;
}
/**
* Calculate the Circulation Tax.
* #return Returns the value of the Environmental Charge multiplied by the Cilinder Capacity of the vehicle.
*/
public double calculateCirculationTax(){
return ENVIRONMENTAL_CHARGE_OMISSION*cilinderCapacity;
}
/**
* Classify the vehicle based on the age.
* If the result given by the calculateAge method is minor than the AGE_RECENT variable(3), then it will
return "Recent"
* If the result is between Age_RECENT and AGE_CLASSIC(20), then it will say "Contemporary"
* If none of the IFs apply, it will return "Classic".
**/
public static String vehicleRating(Vehicle vehicle) {
if(vehicle.calculateAge() < Vehicle.AGE_RECENT) {
return Vehicle.RATING_RECENT; }
else if ((vehicle.calculateAge()>=Vehicle.AGE_RECENT)&&(vehicle.calculateAge()<=Vehicle.AGE_CLASSIC)){
return Vehicle.RATING_CONTEMPORY;}
else
return Vehicle.RATING_CLASSIC;
}
#Override
public String toString() {
return "Vehicle{" + "registration=" + registration + ", registrationYear=" + registrationYear + ", consumption=" + consumption + ", autonomy=" + autonomy + ", cilinderCapacity=" + cilinderCapacity + '}';
}
}

A setter that takes no arguments is simply a method, not a setter. In order to work as a setter a method must take a parameter that matches the type of the value being set - in your case, that would be int:
public static void setAgeRecent(int age) {
AGE_RECENT = age;
}
Note a few things here:
Since AGE_RECENT is static, setAgeRecent should be static
Since AGE_RECENT and setAgeRecent are static members of the same class Vehicle, you do not need to qualify AGE_RECENT with Vehicle
Now users of your class would be able to call your static setter as follows:
Vehicle.setAgeRecent(3);

A static varible, or class variable, may be used without the need to create an instance of that class. But its value may be changed freely at runtime.
A final variable is not a variable in a true sense, because it's value can't be changed at runtime.
Thus, you may have a set method for a static variable, but never to a final variable.

Insert Data to MySql DB from ArrayList<T>

Can anyone help me do this a bit better, I have an ArrayList with data been added everytime a question is answered in the session by calling the method saveQuestionToPlayersQuestion(), after all questions are answered the savePlayersQuestionsToDB() meth is called. I Have a Table in the schema for that data.
I have it working and saving to database, but don't think its the correct way of doing it.
Can I just Insert the arraylist at once, meaning instead of calling the
ConnectionClass.createPlaySessionInDB(pQ.getPlayer_id(),
pQ.getQuestion_tbl_id(), pQ.getAns(),
pQ.getPlayer_score(), pQ.getPlay_session_id());
for every object that's in the List, Its OK when only 3 question are answered, But what happens if they have to answer 20 or 30+ question. Is there a better way.
My declared ArrayList
private ArrayList<Play_Questions> playQuestionList;
playQuestionList = new ArrayList<Play_Questions>();
Here is the method I call to save each question answered to playQuestionList and the next method savePlayersQuestionsToDB() is the one called to save all the object to the DB using a enhanced for loop.
/**
* add the question to playQuestionList
*/
public void saveQuestionToPlayersQuestion() {
Play_Questions temp = new Play_Questions(playerId, question_tbl_id,
choosenAnswer, scorePerQuestion, nextPlaySessionId);
playQuestionList.add(temp);
playQuestionList.toString();
}
/**
* save the playQuestion to DataBase
*/
public void savePlayersQuestionsToDB() {
for (Play_Questions pQ : playQuestionList) {
if (pQ == null) {
System.out.println("Play Question List is empty");
} else
try {
ConnectionClass.createPlaySessionInDB(pQ.getPlayer_id(),
pQ.getQuestion_tbl_id(), pQ.getAns(),
pQ.getPlayer_score(), pQ.getPlay_session_id());
System.out.println("Worked check DB --->>");
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
System.out
.println("Error with ElbtView savePlayersQuestionsToDB()");
}
}
Here is the method in the Connection Class
public static void createPlaySessionInDB(int player_id,
int question_tbl_id, String ans, int player_score,
int play_session_id) throws SQLException {
String sql = "INSERT INTO player_questions (id, player_id, question_tbl_id, ans, player_score, play_session_id ) VALUES (null,?,?,?,?,?)";
try {
preparedStatement = preparedStatement(sql);
preparedStatement.setInt(1, player_id);
preparedStatement.setInt(2, question_tbl_id);
preparedStatement.setString(3, ans);
preparedStatement.setInt(4, player_score);
preparedStatement.setInt(5, play_session_id);
// execute the SQL statement
preparedStatement.executeUpdate();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
System.out
.println("Problem with ConnectionClass createPlaySessionInDB method: "
+ e.getMessage());
} finally {
// close the connection
getConnection().close();
}
}
Here is the Play_Questions class
public class Play_Questions {
private int player_id;
private int question_tbl_id;
private String ans;
private int player_score;
private int play_session_id;
/**
* Default Constructor
*/
public Play_Questions(){
this(0,0,null,0,0);
}
/**
* #param player_id:
* the players id
* #param question_tbl_id:
* the question id from question table
* #param ans:
* the answer selected by player
* #param player_score:
* the score they achieved for answering
* #param play_session_id:
* the play session id
*/
public Play_Questions(int player_id, int question_tbl_id, String ans,
int player_score, int play_session_id) {
this.player_id = player_id;
this.question_tbl_id = question_tbl_id;
this.ans = ans;
this.player_score = player_score;
this.play_session_id = play_session_id;
}
/**
* #return the player_id
*/
public int getPlayer_id() {
return player_id;
}
/**
* #param player_id the player_id to set
*/
public void setPlayer_id(int player_id) {
this.player_id = player_id;
}
/**
* #return the question_tbl_id
*/
public int getQuestion_tbl_id() {
return question_tbl_id;
}
/**
* #param question_tbl_id the question_tbl_id to set
*/
public void setQuestion_tbl_id(int question_tbl_id) {
this.question_tbl_id = question_tbl_id;
}
/**
* #return the ans
*/
public String getAns() {
return ans;
}
/**
* #param ans the ans to set
*/
public void setAns(String ans) {
this.ans = ans;
}
/**
* #return the player_score
*/
public int getPlayer_score() {
return player_score;
}
/**
* #param player_score the player_score to set
*/
public void setPlayer_score(int player_score) {
this.player_score = player_score;
}
/**
* #return the play_session_id
*/
public int getPlay_session_id() {
return play_session_id;
}
/**
* #param play_session_id the play_session_id to set
*/
public void setPlay_session_id(int play_session_id) {
this.play_session_id = play_session_id;
}
Your help in making me code this a bit better will be greatly appreciate.
Gman

This is my approach , its best you use a very transparent approach that models the problem close to a real life scenario .
public class Question
{
private int question_no ;
// The right answer for this question may be a , b or c
private String question_answer ;
private int question_point ;
public Question()
{
}
/**
* #return the question_id
*/
public int getQuestion_id() {
return question_no;
}
/**
* #param question_id the question_id to set
*/
public void setQuestion_id(int question_id) {
this.question_no = question_id;
}
/**
* #return the question_answer
*/
public String getQuestion_answer() {
return question_answer;
}
/**
* #param question_answer the question_answer to set
*/
public void setQuestion_answer(String question_answer) {
this.question_answer = question_answer;
}
/**
* #return the question_point
*/
public int getQuestion_point() {
return question_point;
}
/**
* #param question_point the question_point to set
*/
public void setQuestion_point(int question_point) {
this.question_point = question_point;
}
}
Now the answer class
/**
*
* Track an answer
*/
public class Answer
{
private String answer ;
// correct or failed
private String status ;
public Answer()
{
}
/**
* #return the answer
*/
public String getAnswer() {
return answer;
}
/**
* #param answer the answer to set
*/
public void setAnswer(String answer) {
this.answer = answer;
}
/**
* #return the status
*/
public String getStatus() {
return status;
}
/**
* #param status the status to set
*/
public void setStatus(String status) {
this.status = status;
}
}
Now the player class that encapsulates all the operations for each player after successful login a player object is added to session , it handles operations like marks , save to db ,etc
/**
*
* encapsulates a player
* Class should be placed in session for web applications
*/
public class Player
{
String username ;
String password ;
// holds all the questions arranged for this player without allowing duplicates in questions
Set questions = new HashSet<Question>();
// map this players question and answer
Map question_answers = new HashMap<Question, Answer>();
/**
*
* Allows you to dynamically set questions for players
* #param questions_
*/
public Player(Set questions_ )
{
this.questions = questions_;
}
// if you want the same set of questions for all players
public Player()
{
}
/**
* Question answered for this particular user
* please note that the player object is in session if it is a web application
* #param q
* #param a
*/
public void answerQuestion(Question q , Answer a)
{
question_answers.put(q, a);
}
/**
*
* The user might go back to a previous question to change an answer
* #param q
* #param a
*/
public void updateAnswer(Question q, Answer a)
{
// remove the question and update it with
if(question_answers.containsKey(q))
{
question_answers.remove(q);
}
// add the new q & a
answerQuestion(q, a);
}
/**
*
* finally save the players data
* here your db model counts it would have to cater for
* each players question and answer , send the batch update using batch prepared statements
*/
public void savePlayerData()
{
// db code is commented because i didnt write db codes
// status int the column will stand for correct or fail
// String save_sql =insert into results(player_id , question_id , answer , status) values(?,?,?,?)
// PreparedStatement pstat = dbConnection.prepareStatement(save_sql);
//dbConnection.setAutoCommit(false);
// if automark is enabled
autoMark();
Iterator it = question_answers.values().iterator();
while(it.hasNext())
{
// fetch each question
Question q = (Question)it.next();
// Fetch each answer based on the question
Answer a = (Answer)question_answers.get(q);
int question_id = q.getQuestion_id();
String answer = a.getAnswer();
String answer_status = a.getStatus();
/**
*
*
* commented cause i would have to write db backing code , lol !
*
* pstat.setInt(1, getUsername());
* pstat.setInt(2, question_id);
* pstat.setString(3 , answer);
* pstat.setString(4 , answer_status)
* pstat.addBatch();
* pstat.executeBatch();
*
*/
}
//dbConnection.setAutoCommit(false);
}
/**
*
* This method can allow your program to auto mark if
* the question and answer if it is based on a , b , c
*/
public void autoMark()
{
Iterator it = question_answers.values().iterator();
while(it.hasNext())
{
// fetch each question
Question q = (Question)it.next();
// Fetch each answer based on the question
Answer a = (Answer)question_answers.get(q);
if(q.getQuestion_answer().equalsIgnoreCase(a.getAnswer()))
{
a.setStatus("Correct");
}
else
{
a.setStatus("Failed");
}
updateAnswer(q, a);
}
}
}
So anytime a player answers a question u call
p.answerQuestion(Question q , Answer a)
The question object is the particular question answered and the answer object is created to ,match the question .
U can also track the users current question by adding a value called current_question on the player class with getter and setter(Question Object) to track the current question in cases where the user might go back to a previous question you can then call
p.updateAnswer(Question q, Answer a)
Same thing u pass the particular question an d the new answer object
p.savePlayerData()
Saves data to the db
p.autoMark()
This method is called in the p.savePlayerData() method before the records are saved so the db only holds final assessment & marked records , This can come in handy for intelligent reporting such as who has the highest score . Thats it if you have extra questions you can contact me tyger2007#gmail.com.

Ok I did manage to achieve what I was trying to do, here is the revised code to help others that have the same problem. This is not the definite way to do this just the only way I know at this time to acheive what I need to. If anyone has a nice, faster way of doing this I would love to know. Got some inspiration from this thread here Java: Insert multiple rows into MySQL with PreparedStatement
Here is the method I call to save each question answered to playQuestionList and the next method savePlayersQuestionsToDB(), Instead of doing the work here I pass the Arraylist to the Connection Class and loop through it there.
/**
* add the question to playQuestionList
*/
public void saveQuestionToPlayersQuestion() {
Play_Questions temp = new Play_Questions(playerId, question_tbl_id,
choosenAnswer, scorePerQuestion, nextPlaySessionId);
playQuestionList.add(temp);
}
/**
* save the playQuestion to DataBase
*/
public void savePlayersQuestionsToDB() {
try {
ConnectionClass.savePlaySessionInDB(playQuestionList);
System.out.println("Worked check DB --->>");
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
System.out
.println("Error with ElbtView savePlayersQuestionsToDB()");
}
}
and here is the method in the ConnectionClass
/**
* Creates a batch using addBatch()and then executes it by calling
* ececuteBatch()
*
* #param playQuestions
* the ArrayList<T> to be added to batch and then saved to DB
* #throws SQLException
* when executing the the batch
*/
public static void savePlaySessionInDB(
ArrayList<Play_Questions> playQuestions) throws SQLException {
try {
String sql = "INSERT INTO player_questions (id, player_id, question_tbl_id, ans, player_score, play_session_id ) VALUES (null,?,?,?,?,?)";
preparedStatement = preparedStatement(sql);
for (int i = 0; i < playQuestions.size(); i++) {
Play_Questions playQuestion = playQuestions.get(i);
preparedStatement.setInt(1, playQuestion.getPlayer_id());
preparedStatement.setInt(2, playQuestion.getQuestion_tbl_id());
preparedStatement.setString(3, playQuestion.getAns());
preparedStatement.setInt(4, playQuestion.getPlayer_score());
preparedStatement.setInt(5, playQuestion.getPlay_session_id());
preparedStatement.addBatch();
if ((i + 1) % 100 == 0) {
preparedStatement.executeBatch(); // excute every 100 items
}
}
preparedStatement.executeBatch();
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
System.out
.println("Problem with ConnectionClass savePlaySessionInDB(ArrayList<Play_Questions> playQuestions) method: "
+ e.getMessage());
} finally {
// close the connection
getConnection().close();
}
}
Defiantly open to a much better suggestion.
Gman

I must say that as this solution actually works perfectly now , in the long hol it might still pose some problems it actually depends on the nature of your application , is it an application that will be deployed and used by a lot of users ? or its just a test application ?, Anyway i do advise that you model your objects properly as this is the most important thing in object oriented programming ,
My suggestions :
Isolate Question , Player , Answer Objects , Having Objects Like Play_Question will make your application difficult to extend dynamically .
Use an Iterator for your loops , its been optimized to perform better than for loops especially in collection.
For me i naturally use a singleton connection class if it is a desktop application & JNDI if its a web application , the connection class uses a connection pool so my application does not open a new connection for every db request , it makes your application super fast in db request [http://jolbox.com/ bonecp connection pooling for Desktop apps if web use JNDI ]
Maps are very easy to use its a case of key/value pairs , All the same nice work and have fun. .

It's ok ,spent quite some time developing applications that generally I always develop to scale ,lol ,I used iterators in the Players class in the method savePlayerData() u can always use it with your collection classes .

Cannot make static reference to non-static object

This is my first Java project.
So I'm working on my own simulation project, and some of my core stuff has gone awry. I have two classes I'm focusing on right now - settlement and townRey, which extends settlement.
The error is thrown when I try
System.out.println(townRey.returnStrength());
Here are my two relevant classes:
settlement:
public class settlement
{
//
//
// VARIABLES
//
//
/**
* The town's unique name.
*/
public String name;
/**
* The settlement's location in latitude (N-S)
*/
public int latitude;
/**
* The settlement's location in longitude (E-W)
*/
public int longitude;
/**
* What faction a town or village is aligned to. This determines production and consumption, mostly.
*/
public String faction;
/**
* What a specific village or town produces.
*/
public String[] production;
/**
* What a specific town consumes (villages don't consume)
*/
public String[] consumption;
/**
* How dangerous a specific town is with bandits
* A 1-10 scale, with 10 being the most dangerous.
* Any town with a danger over 8 can be raided and destroyed temporarily by bandits.
* Being raided successfully depends on the Strength of a town.
*/
public int danger;
/**
* How much a town takes in taxes.
*/
public float tax;
/**
* How easily a town is raided by bandits.
* If a bandit raid has a lower strength than the town, then the town wins.
*/
public int strength;
//
//
// METHODS
//
//
public int returnLatitude()
{
return latitude;
}
public int returnLongitude()
{
return longitude;
}
public String returnFaction()
{
return faction;
}
public String[] returnProduction()
{
return production;
}
public String[] returnConsumption()
{
return consumption;
}
public int returnDanger()
{
return danger;
}
public float returnTax()
{
return tax;
}
public int returnStrength()
{
return strength;
}
}
and townRey:
public class townRey extends settlement
{{
name = "Rey";
latitude = 5;
longitude = 5;
String faction = "Nord";
String[] production;
String[] consumption;
danger = 1;
tax = 0.05F;
strength = 6;
}}
EDIT:: Thanks for all the help! I fixed all issues now. Below is 'Settlement' and 'Start'.
public class Settlement
{
//
//
// VARIABLES
//
//
/**
* The town's unique name.
*/
public String name;
/**
* The settlement's location in latitude (N-S)
*/
public int latitude;
/**
* The settlement's location in longitude (E-W)
*/
public int longitude;
/**
* What faction a town or village is aligned to. This determines production and consumption, mostly.
*/
public String faction;
/**
* What a specific village or town produces.
*/
public String[] production;
/**
* What a specific town consumes (villages don't consume)
*/
public String[] consumption;
/**
* How dangerous a specific town is with bandits
* A 1-10 scale, with 10 being the most dangerous.
* Any town with a danger over 8 can be raided and destroyed temporarily by bandits.
* Being raided successfully depends on the Strength of a town.
*/
public int danger;
/**
* How much a town takes in taxes.
*/
public float tax;
/**
* How easily a town is raided by bandits.
* If a bandit raid has a lower strength than the town, then the town wins.
*/
public int strength;
//
//
// METHODS
//
//
public int returnLatitude()
{
return latitude;
}
public int returnLongitude()
{
return longitude;
}
public String returnFaction()
{
return faction;
}
public String[] returnProduction()
{
return production;
}
public String[] returnConsumption()
{
return consumption;
}
public int returnDanger()
{
return danger;
}
public float returnTax()
{
return tax;
}
public int returnStrength()
{
return strength;
}
}
and Start, where I create 'townRey' then access a bit of data in two different ways.
public class Start
{
public static void main(String[] args)
{
//Creates 'Rey'
Settlement townRey = new Settlement();
townRey.name = "Rey";
townRey.latitude = 5;
townRey.longitude = 5;
townRey.faction = "Nord";
townRey.danger = 1;
townRey.tax = 0.05F;
townRey.strength = 6;
//This calls the returnLongitude method from Settlement, and is the 'proper' way to do it.
System.out.println(townRey.returnLongitude());
//This also works.
System.out.println(townRey.longitude);
//Thanks for the help!
}
}

townRey shouldn't be extending settlement. You should be declaring it as an instance of settlement in some method, as follows:
townRey = new settlement();
townRey.name = "Rey";
...
townRey.strength = 6;
Or, better still, making a new constructor for settlement that takes the different fields as inputs.
Also, a style note: Generally, in Java, classes should begin with a capital letter, so Settlement rather than settlement might make a better name.

You should define a townRey object then use this object to call returnStrength
townRey mytownRey = new townRey();
System.out.println(townRey.returnStrength());

I expect you want townRey to be an instance of settlement, not a subclass. Unless you want to have multiple copies of townRey. Replace the line public class townRey extends settlement with settlement townRey = new settlement(), and add a semicolon after }}. Leave everything else the same.

public class mainclss()
{
public static void main(String arg[])
{
townRey= new settlement();
//you can do sth you like
}
}
create a new class to check.DO NOT start Java with Class!It is a little difficult.

Create a separate class with main() method. Inside this method, you should create an object of townRey, in order to access the method returnStrength(). You can't access it using the class name 'townRay' if you are doing so. So Add this class with the code below:
public class MainClass {
public static void main(String[] args) {
townRey tr = new townRey();
System.out.println( tr.returnStrength () );
}
}
This worked fine with me. So you can safely use it.
NOTE: You should learn by practice to start each word in your class name with a capital letter such as Settlement and TownRey. Good Luck!

Accessing values from another thread

My question is: How do I access values from another thread?
I have two .java files, Main.java and TrackHands.java
Main.java
/**
* This is the main class, it is used to start the program. The only use of this
* is to make everything more organized.
*/
package Kinect;
//import processing.core.PApplet;
/**
* #author Tony Nguyen <Tony.Nguyen#HvA.nl>
*
*/
public class Main
{
public static void main(String _args[])
{
Thread trackHands = new Thread(new TrackHands());
trackHands.start();
}
}
TrackHands.java
/*
* This uses the normal Java layout to track the user and prints out the coordinates of the left and right hand
*/
package Kinect;
import SimpleOpenNI.*;
import processing.core.PApplet;
import processing.core.PVector;
/**
* #author Tony Nguyen <Tony.Nguyen#HvA.nl>
* #version 1.0
*/
public class TrackHands extends PApplet implements Runnable
{
private int handLeftX, handLeftY = 0; // Holds the coordinates of the left hand
SimpleOpenNI kinect = new SimpleOpenNI(this); // kinect object
/**
* Constructor Takes no parameters
*/
public TrackHands()
{
}
/**
* run This will be executed when the thread starts
*/
#Override
public void run()
{
IntVector userList = new IntVector(); // Make a vector of ints to store the list of users
PVector leftHand = new PVector(); // Make a vector to store the left hand
PVector convertedLeftHand = new PVector();
kinect.enableDepth();
kinect.enableUser(SimpleOpenNI.SKEL_PROFILE_ALL);
kinect.setMirror(true);
while (true)
{
kinect.update();
kinect.getUsers(userList); // Write the list of detected users into the vector
if (userList.size() > 0) // Checks if a user is found
{
int userId = userList.get(0); // Get first user
if (kinect.isTrackingSkeleton(userId)) // If successfully calibrated
{
kinect.getJointPositionSkeleton(userId,
SimpleOpenNI.SKEL_LEFT_HAND, leftHand); // Put the position of the left hand into that vector
kinect.convertRealWorldToProjective(leftHand,
convertedLeftHand);
this.handLeftX = round(convertedLeftHand.x);
this.handLeftY = round(convertedLeftHand.y);
}
}
}
}
// User-tracking callbacks!
public void onNewUser(int userId)
{
System.out.println("Start pose detection");
kinect.startPoseDetection("Psi", userId);
}
public void onEndCalibration(int userId, boolean successful)
{
if (successful)
{
System.out.println(" User calibrated !!!");
kinect.startTrackingSkeleton(userId);
} else
{
System.out.println(" Failed to calibrate user !!!");
kinect.startPoseDetection("Psi", userId);
}
}
public void onStartPose(String pose, int userId)
{
System.out.println("Started pose for user");
kinect.stopPoseDetection(userId);
kinect.requestCalibrationSkeleton(userId, true);
}
}
I have tried to use a getter and a setter to get the values from TrackHands.java into another thread.
Tried creating objects and passing the values as parameters, but then my program will not use these new values in the run() method.

To get values from TrackHands, use a get method that accesses an instance variable that is set in run()
class TrackHands {
Object output;
public void run() {
while(true) {
output = new Object();
}
}
public Object getOutput() {
return output;
}
}
Pass TrackHands into your consumer object and use it to call get getOutput() method.
Passing values in is a bit trickier, because you might cause race condition. Try something like this
class TrackHands {
Object input = null;
public boolean setInput(Object input) {
if(this.input == null) {
this.input = input;
return true;
} else {
return false;
}
}
}
When your run() method uses input, set it to null so that another thread can pass in another input. Your producer thread will use this loop to pass in input:
public void sendInput(TrackHands th, Object input) {
boolean done = false;
while(!done) {
done = th.setInput(input);
}
}
This will keep trying to pass in input until it succeeds.
setInput uses the synchronized keyword so that only one thread can call this method at once, otherwise you'll get a race condition.

A friend of mine solved my problem.
I want to thank everyone for helping me!
Main.java
/**
* This is the main class, it is used to start the program. The only use of this
* is to make everything more organized.
*/
package Kinect;
//import processing.core.PApplet;
/**
* #author Tony Nguyen <Tony.Nguyen#HvA.nl>
*
*/
public class Main
{
public static void main(String _args[])
{
// PApplet.main(new String[]
// {
// Sensor.class.getName()
// });
ValueStore valueStore = new ValueStore(); // ADDED THIS LINE
Thread trackHands = new Thread(new TrackHands(valueStore)); // ADDED THIS LINE
trackHands.start();
}
}
TrackHands.java
/*
* This uses the normal Java layout to track the user and prints out the coordinates of the left and right hand
*/
package Kinect;
import SimpleOpenNI.*;
import processing.core.PApplet;
import processing.core.PVector;
/**
* #author Tony Nguyen <Tony.Nguyen#HvA.nl>
* #version 1.0
*/
public class TrackHands extends PApplet implements Runnable
{
private int handLeftX, handLeftY, handRightX, handRightY = 0; // Holds the coordinates of the left hand
SimpleOpenNI kinect = new SimpleOpenNI(this); // kinect object
private ValueStore valuesStore; // ADDED THIS LINE
/**
* Constructor Takes no parameters
*/
public TrackHands()
{
}
public TrackHands(ValueStore valuesStore)
{
this.valuesStore = valuesStore;
}
/**
* run This will be executed when the thread starts
*/
#Override
public void run()
{
IntVector userList = new IntVector(); // Make a vector of ints to store the list of users
PVector leftHand = new PVector(); // Make a vector to store the left hand
PVector rightHand = new PVector(); // Make a vector to store the right hand
PVector convertedLeftHand = new PVector(); // Make a vector to store the actual left hand
PVector convertedRightHand = new PVector(); // Make a vector to store the actual right hand
kinect.enableDepth();
kinect.enableUser(SimpleOpenNI.SKEL_PROFILE_ALL);
kinect.setMirror(true);
while (true)
{
kinect.update();
kinect.getUsers(userList); // Write the list of detected users into the vector
if (userList.size() > 0) // Checks if a user is found
{
int userId = userList.get(0); // Get first user
if (kinect.isTrackingSkeleton(userId)) // If successfully calibrated
{
kinect.getJointPositionSkeleton(userId,
SimpleOpenNI.SKEL_LEFT_HAND, leftHand); // Put the position of the left hand into that vector
kinect.getJointPositionSkeleton(userId,
SimpleOpenNI.SKEL_RIGHT_HAND, rightHand); // Put the position of the left hand into that vector
kinect.convertRealWorldToProjective(leftHand,
convertedLeftHand);
kinect.convertRealWorldToProjective(rightHand,
convertedRightHand);
this.handLeftX = round(convertedLeftHand.x);
this.handLeftY = round(convertedLeftHand.y);
this.handRightX = round(convertedRightHand.x);
this.handRightY = round(convertedRightHand.y);
valuesStore.setHandValues(handLeftX, handLeftY, handRightX, handRightY); // ADDED THIS LINE
}
}
}
}
// User-tracking callbacks!
public void onNewUser(int userId)
{
System.out.println("Start pose detection");
kinect.startPoseDetection("Psi", userId);
}
public void onEndCalibration(int userId, boolean successful)
{
if (successful)
{
System.out.println(" User calibrated !!!");
kinect.startTrackingSkeleton(userId);
} else
{
System.out.println(" Failed to calibrate user !!!");
kinect.startPoseDetection("Psi", userId);
}
}
public void onStartPose(String pose, int userId)
{
System.out.println("Started pose for user");
kinect.stopPoseDetection(userId);
kinect.requestCalibrationSkeleton(userId, true);
}
}
Then added a class to store the values so another class can access it.
ValueStore.java
/*
* To change this template, choose Tools | Templates
* and open the template in the editor.
*/
package Kinect;
/**
*
* #author Tony Nguyen <Tony.Nguyen#HvA.nl>
*/
public class ValueStore
{
private int leftX, leftY, rightX, rightY = 0;
public void setHandValues(int leftX, int leftY, int rightX, int rightY)
{
this.leftX = leftX;
this.leftY = leftY;
this.rightX = rightX;
this.rightY = rightY;
}
public int getLeftX()
{
return this.leftX;
}
}