Develop Reference

Changing fields of class in java

So, I'm still learning java and coding so the resolution may be obvious but I just can't see it.
I'm writing a code about stars and constelations for uni assignment.
package com.company;
import java.util.*;
public class Main {
static public class Constellation {
public List<Star> constellation;
public String nameOfConstellation;
public Constellation(List<Star> constellation, String nameOfConstellation) {
this.constellation = constellation;
this.nameOfConstellation = nameOfConstellation;
}
public List<Star> getConstellation() {
return constellation;
}
}
static public class Star {
// private String categoryName;
private Constellation constellation;
private String nameOfConstelation;
public String getCategoryName() {
int index = constellation.getConstellation().indexOf(this);
String categoryName;
return categoryName = GreekLetter.values[index] + " " + this.constellation.nameOfConstellation;
}
public void deleteStar(Star x) {
this.constellation.constellation.remove(x);
}
}
public enum GreekLetter {
alfa,
beta,
gamma,
delta,
epsilon,
dzeta,
eta;
static public final GreekLetter[] values = values();
}
public static void main(String[] args)
{
Star x = new Star();
List<Star> fishCon = new ArrayList<>();
Constellation Fish = new Constellation(fishCon, "Fish");
x.constellation=Fish;
fishCon.add(x);
x.getCategoryName();
Star y = new Star();
y.constellation=Fish;
fishCon.add(y);
y.getCategoryName();
x.deleteStar(x);
for (Star w : Fish.constellation)
{
System.out.println(w.getCategoryName());
}
}
}
My point is to Update field categoryName after deleting one star. categoryName value is set in order of adding another star. For example I have first star - the name will be Alfa + nameOfConstelation. Second star - Beta + nameOfConstelation. When I call method deleteStar() I want to update all categoyName of my stars in constelation. Calling methods in deleteStar() doesn't work probably due to add() in setCategoryName. I would really appreciate any hints!

Since this appears to be homework, I am not posting code in this answer but rather giving suggestions that can help you create your own workable code:
Create a class called Constellation that holds the Stars in an List<Star> starList = new ArrayList<>();
Give Constellation a public List<Star> getStarList() method
Give each Star a Constellation field to hold the Constellation that contains this Star
Give each Star a getCategoryName() method that gets the Constellation object, iterates through its starList using a for-loop until it finds the this Star, and then that returns the appropriate name based on the index of the Star in the list.
Thus, if a Star is removed from the starList, the category names of all the other Stars held by that Constellation will update automatically and dynamically
Also,
You can give Constellation a public void deleteStar(Star star) method where it removes the Star parameter from its starList
You can also give Star a public void deleteFromConstellation() method where it checks its Constellation field, constellation, and if not null, calls constellation.deleteStar(this); and then sets the constellation field to null
Get rid of the private String categoryName; field in Star. This should be a calculated field, meaning the public String getCategoryName() does not return a field, but a String based on code (as described above).
It first checks that Star's constellation field is not null
It then gets the index of the Star in the Constellation's starList (I have given my Constellation class a public int getIndexOfStar(Star star) method.
It then uses this, the GreekLetter class, and the constellation.getName() method to create a String to return
Done.
Since you've figured this out, this is another way to code it:
public class SkyMain {
public static void main(String[] args) {
Constellation fish = new Constellation("Fish");
Star x = new Star();
Star y = new Star();
fish.addStar(x);
fish.addStar(y);
System.out.println("before removing x");
System.out.println("x category name: " + x.getCategoryName());
System.out.println("y category name: " + y.getCategoryName());
System.out.println("fish constellation: " + fish);
fish.removeStar(x);
System.out.println();
System.out.println("after removing x");
System.out.println("x category name: " + x.getCategoryName());
System.out.println("y category name: " + y.getCategoryName());
System.out.println("fish constellation: " + fish);
}
}
public class Star {
private Constellation constellation;
public void setConstellation(Constellation constellation) {
this.constellation = constellation;
}
public void removeFromConstellation() {
if (constellation != null) {
constellation.removeStar(this);
}
}
public String getCategoryName() {
if (constellation != null) {
int index = constellation.getIndexOfStar(this);
return GreekLetter.getGreekLetter(index).getName() + " " + constellation.getName();
} else {
return "";
}
}
#Override
public String toString() {
return getCategoryName();
}
}
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
public class Constellation implements Iterable<Star> {
private String name;
private List<Star> starList = new ArrayList<>();
public Constellation(String name) {
this.name = name;
}
public String getName() {
return name;
}
public List<Star> getStarList() {
return starList;
}
public void addStar(Star star) {
starList.add(star);
star.setConstellation(this);
}
public void removeStar(Star star) {
if (starList.contains(star)) {
starList.remove(star);
star.setConstellation(null);
}
}
public int getIndexOfStar(Star star) {
return starList.indexOf(star);
}
#Override
public Iterator<Star> iterator() {
return starList.iterator();
}
#Override
public String toString() {
return "Constellation [name=" + name + ", starList=" + starList + "]";
}
}
public enum GreekLetter
{
ALPHA("alpha", 0),
BETA("beta", 1),
GAMMA("gamma", 2),
DELTA("delta", 3),
EPSILON("epsilon", 4),
ZETA("zeta", 5),
ETA("eta", 6);
private String name;
private int index;
private GreekLetter(String name, int index) {
this.name = name;
this.index = index;
}
public String getName() {
return name;
}
public int getIndex() {
return index;
}
public static GreekLetter getGreekLetter(int index) {
if (index < 0 || index > values().length) {
throw new IllegalArgumentException("for index " + index);
} else {
return values()[index];
}
}
}

Setters And Getters to different Class

My problem is that, simply I don't know what code to use to get my value from my getX method to my other classses main method.
package hangman;
public class Hangman {
private int triesLimit;
private String word;
public void setTriesLimit(int triesLimit) {
this.triesLimit = triesLimit;
}
public void setWord(String word) {
this.word = word;
}
public int getTriesLimit() {
return this.triesLimit;
}
public String getWord() {
return this.word;
}
#Override
public String toString() {
return ("Enter Secret Word " + this.getWord()
+ ".\nEnter max # of tries (Must be under 7) "
+ this.getTriesLimit());
}
}
Thats from the sub-class and I am trying to store the value of the triesLimit into the main of this classes main method
package hangman;
public class PlayHangman {
public static void main(String[] args) {
Hangman hangman = new Hangman();
Scanner scn = new Scanner(System.in);
int triesCount = 0;
int correctCount = 0;
hangman.toString();
int triesLimit = hangman.getTriesLimit();
String secretWord = hangman.getWord();
StringBuilder b = new StringBuilder(secretWord.length());
for (int i = 0; i < secretWord.length(); i++) {
b.append("*");
}
char[] secrectStrCharArr = secretWord.toCharArray();
int charCnt = secretWord.length();
for (int x = 0; triesCount < triesLimit; triesCount++) {
while (charCnt >= 0) {
System.out.println("Secrect Word :" + b.toString());
System.out.println("Guess a letter :");
char guessChar = scn.next().toCharArray()[0];
for (int i = 0; i < secrectStrCharArr.length; i++) {
if (guessChar == secrectStrCharArr[i]) {
b.setCharAt(i, guessChar);
correctCount++;
} else if (guessChar != secrectStrCharArr[i]) {
triesCount++;
System.out.println("Incorrect: " + triesCount);hangmanImage(triesCount,correctCount);
}
}
}
}
}
I tried looking it up on here but couldn't find setters and getters used in a sub/superclass

You need to create an instance of the class in the main method to access the variables and method available in that class like so
public class PlayHangman {
public static void main(String[] args) {
Hangman hangman = new Hangman();
hangman.setTriesLimit(2)
int value = hangman.getTriesLimit();
}
You can look into static keyword to access the value directly but that requires a bit more understanding of OOP's and JAVA.
This should work fine.
Hope it helps :)
EDITED
ToString method is just to convert everything in your model class to String which you have done correctly,but you have implemented incorrectly.... Change your ToString content so
#Override
public String toString() {
return ("The Secret Word you entered: " + this.getWord()
+ ".\n The max # of tries (Must be under 7): "
+ this.getTriesLimit());
}
You have initialized Scanner which does what you want, to ask the user to enter the values but again you haven't implemented it so add this to your main method
Scanner scn = new Scanner(System.in);
hangman.setTriesLimit(scn.nextInt());
hangman.setWord(scn.next());
hangman.toString()//Will work now
Trial and error is your best friend now :)
and Google some of the issues rather than waiting for an answer :)

Like rohit said, this is as simple as understand the basics of OOP, specific the encapsulation.
If you want to get a little deeper into OOP patterns, you could use the Observer pattern. This allows you to change the status of any class instance, even if they're not related by inheritance, aggregation, etc.
You can scale the solution by making List of Observer
Your observable interface
public interface IObservable {
// Set the observer
public void setObserver(IObserver iObserver);
// Notify the observer the current status
public void notifyObserver();
}
Your observer interface
public interface IObserver {
public void update(boolean status);
}
Your observer implementation
public class PlayHangman implements IObserver {
private boolean status = false;
public void printStatus() {
System.out.println("Status: " + (this.status ? "Win" : "Lose"));
}
#Override
public void update(boolean status) {
// The instance status is updated
this.status = status;
// Print the current status
this.printStatus();
}
}
Your observable implementation
public class Hangman implements IObservable{
private String goalWord = "";
private String currentWord = "";
private int triesLimit = 0;
private int tries = 0;
private IObserver iObserver;
public Hangman(String goalWord, int triesLimit) {
this.goalWord = goalWord;
this.triesLimit = triesLimit;
}
public void setCurrentWord(String currentWord) {
this.currentWord = currentWord;
this.notifyObserver();
}
public void addTry() {
this.tries++;
this.notifyObserver();
}
#Override
public void setObserver(IObserver iObserver) {
this.iObserver = iObserver;
}
#Override
public void notifyObserver() {
// True = win
this.iObserver.update(this.tries < this.triesLimit &&
this.goalWord.equals(this.currentWord));
}
}
Your Main class
public class Main{
public static void main(String[] args) {
// PlayHangman (game status)
PlayHangman playHangman = new PlayHangman();
// Hangman initializes with a goalWord and the triesLimit
Hangman hangman = new Hangman("HangmanJava", 5);
// Set the observer
hangman.setObserver(playHangman);
// During the game you just can set the current word and add a try
// You're not setting the status directly, that's the magic of the Observer pattern
hangman.setCurrentWord("Hang");
hangman.addTry();
hangman.setCurrentWord("HangmanJava");
}
}
Hope this helps and enjoy Java

Why does this not print the String inside the object?

This program is used for a flash card application. My constructor is using a linked list, but the problem is that when I use a method that list the cards inside a specific box it is not printing the desired result. The system should print "Ryan Hardin". Instead it is printing "Box$NoteCard#68e86f41". Can someone explain why this is happening and what I can do to fix this? I have also attached both my box and note card classes.
import java.util.LinkedList;
import java.util.ListIterator;
public class Box {
public LinkedList<NoteCard> data;
public Box() {
this.data = new LinkedList<NoteCard>();
}
public Box addCard(NoteCard a) {
Box one = this;
one.data.add(a);
return one;
}
public static void listBox(Box a, int index){
ListIterator itr = a.data.listIterator();
while (itr.hasNext()) {
System.out.println(itr.next());
}
}
public static void main(String[] args) {
NoteCard test = new NoteCard("Ryan", "Hardin");
Box box1 = new Box();
box1.addCard(test);
listBox(box1,0);
}
}
This is my NoteCard Class
public class NoteCard {
public static String challenge;
public static String response;
public NoteCard(String front, String back) {
double a = Math.random();
if (a > 0.5) {
challenge = front;
} else
challenge = back;
if (a < 0.5) {
response = front;
} else
response = back;
}
public static String getChallenge(NoteCard a) {
String chal = a.challenge;
return chal;
}
public static String getResponse(NoteCard a) {
String resp = response;
return resp;
}
public static void main(String[] args) {
NoteCard test = new NoteCard("Ryan", "Hardin");
System.out.println("The challenge: " + getChallenge(test));
System.out.println("The response: " + getResponse(test));
}
}

Try to override the method toString() in your class NoteCard.
#Override
public String toString()
{
//Format your NoteCard class as an String
return noteCardAsString;
}

In First place you are making too much use of static keyword. I am not sure whether you need that. Anyways create two instance variable front and back and assign value to it in constructor of NoteCard class, Also implement toString method
public class NoteCard {
public static String challenge;
public static String response;
public String front;
public String back;
public NoteCard(String front, String back) {
//your code
this.front = front;
this.back = back;
}
#Override
public String toString()
{
//return "The challenge:" + challenge + " " + "The response: " + response;
return "The Front:" + front + " " + "The Back: " + back;
}
Note: Since the instance method toString() is implicitly inherited
from Object, declaring a method toString() as static in a sub type
causes a compile-time error SO DON'T MAKE THIS METHOD STATIC

relation between two classes (german code) [closed]

Closed. This question does not meet Stack Overflow guidelines. It is not currently accepting answers.
This question does not appear to be about programming within the scope defined in the help center.
Closed 9 years ago.
Improve this question
I want to make an array with which I can create some instances of the class Schiff (Ship) by using the class Flotte (Armada). Somehow it does not work. Which method is more useful? addShiff or addSchiff2?
public class Schiff
{
private String material;
private int kanonen;
private int ursprungsMäste;
private int mästeStehenNoch;
public Schiff (String material, int kanonen, int mäste)
{
this.material = material;
this.kanonen = kanonen;
ursprungsMäste = mäste;
mästeStehenNoch = mäste;
}
public String gibMaterial()
{
return material;
}
public void mastGetroffen(int wieVieleTreffer)
{
mästeStehenNoch = mästeStehenNoch - wieVieleTreffer;
}
public void wieVieleMäste ()
{
System.out.println("Es stehen noch " + mästeStehenNoch + " Mäste!");
}
}
+++++++
public class Flotte
{
private Schiff [] flottenArray;
public Flotte ()
{
flottenArray = new Schiff [100];
}
public void addSchiff (String material, int kanonen, int ursprungsMäste)
{
for (int zahl = 0; zahl<flottenArray.length; zahl++)
{
if (flottenArray[zahl] == null)
{
flottenArray[zahl] = new Schiff (material, kanonen, ursprungsMäste);
}
}
}
public void addSchiff2 (Schiff neuesSchiff)
{
for (int zahl = 0; zahl<flottenArray.length; zahl++)
{
if (flottenArray[zahl] == null)
{
flottenArray[zahl] = neuesSchiff;
}
}
}
public void gegnerischerFeuerAngriff ()
{
for (Schiff schiff : flotte)
{
if (schiff.gibMaterial().equals("holz"))
{
flottenArray.remove(schiff);
}
}
}
}

What exactly does not work?
Looks good to me.
My feeling is that you can drop the addSchiff (String material, int kanonen, int ursprungsMäste) method because:
One: It is just another way of writing addSchiff2(new Schiff(material, kanonen, ursprungsMäste)) and this is also how it should be coded to avoid repeating yourself:
public void addSchiff (String material, int kanonen, int ursprungsMäste)
{
addSchiff2(new Schiff(material, kanonen, ursprungsMäste))
}
Two: If you later decide to add fields to class Schiff you will have to change the interface of Flotte if you keep the method that constructs a Schiff instance from passed parameters. This is not the case if you just have a method that takes a Schiff instance. So getting rid of addSchiff() decreased inter-class coupling, which is gut.
Klar zur Halse!

An Arraylist of Arrays or os there a better way?

So thanks to the wonderful people here i've managed to get something semi workable, still have a couple bugs but maybe you guys can help me figure it out. So far none of the solution provided were a exact match (which is why i havent up voted them) but they did help me look at things in a new way and get things moving forward. So here is the current problem.
First the code then the explination
RaceButtons[RaceCounter] = new JToggleButton();
RaceButtons[RaceCounter].setIcon(RCiconSM);
RaceButtons[RaceCounter].setBorder(BorderFactory.createEmptyBorder());
RaceButtons[RaceCounter].setContentAreaFilled(false);
RaceButtons[RaceCounter].setActionCommand(temp_race.getRaceNameString(RaceCounter));
RaceButtons[RaceCounter].addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent ae) {
Race race = new Race(1, 1, GenderList[PHYSICAL_SEX]);
race.setRaceID(race.getRaceIDFromString(ae.getActionCommand()));
//System.out.println(race.getraceID());
if (RaceButtons[race.getraceID()].isSelected()){
RaceButtons[race.getraceID()].setBorderPainted(true);
RaceButtons[race.getraceID()].setBorder(new LineBorder(Color.blue,2));
MyRaceArray.add(new Race(race.getraceID(), 1, GenderList[PHYSICAL_SEX]));
}else{
RaceButtons[race.getraceID()].setBorderPainted(false);
};
So first i create an array of Toggle buttons and when you click it it draw the border and then getting it's info i can add it to the array for races but this lives me with another problem i cant quite figure the logic off. Namly if there are already selected button it adds another instances to the button, it shouldn't do that it should ignore iexaisting entries but that means i have to check the arry for a matching object of type Race withthe same info right? What's the best way to do that?
And when you deselect it how do i remove that same object.

This is how your code should look like with a Race class:
import java.util.ArrayList;
import java.util.List;
public class Race {
private int raceID;
private double purity;
private int strMod;
private int dexMod;
private int conMod;
private int wisMod;
public int getRaceID() {
return raceID;
}
public void setRaceID(int raceID) {
this.raceID = raceID;
}
public double getPurity() {
return purity;
}
public void setPurity(double d) {
this.purity = d;
}
public int getStrMod() {
return strMod;
}
public void setStrMod(int strMod) {
this.strMod = strMod;
}
public int getDexMod() {
return dexMod;
}
public void setDexMod(int dexMod) {
this.dexMod = dexMod;
}
public int getConMod() {
return conMod;
}
public void setConMod(int conMod) {
this.conMod = conMod;
}
public int getWisMod() {
return wisMod;
}
public void setWisMod(int wisMod) {
this.wisMod = wisMod;
}
#Override
public String toString() {
return "Race [raceID=" + raceID + ", purity=" + purity + ", strMod="
+ strMod + ", dexMod=" + dexMod + ", conMod=" + conMod
+ ", wisMod=" + wisMod + "]";
}
public static void main(String args[]) {
//create a list of race objects
List<Race> raceCollection = new ArrayList<Race>();
//create a race object
Race race = new Race();
race.setRaceID(1);
race.setPurity(0.75);
race.setStrMod(5);
race.setDexMod(7);
race.setConMod(-2);
race.setWisMod(3);
//add race object to collection
raceCollection.add(race);
//You can create and add multiple objects of race to the collection
//Iterate your list and print the objects
for(Race raceObj:raceCollection) {
System.out.println(raceObj);
}
}
}

You will be able to make it work using an ArrayList of arrays, but that possibly isn't the best way in the long run. It can be very fiddly and error-prone to deal with - what happens when you insert a new race or attribute, but forget to to change the index somewhere?
Arrays and ArrayLists are usually best reserved for situations where you actually have a sequence / list (often with a meaningful sequence order).
In your case I'd be more inclined to adopt a prototype model. Typically in Java you would represent each race with a HashMap (or a data structure containing a HashMap), there the map represents the relationship between the "Attribute ID" and the "Default Value".
Creating a new elf is then just a case of initialising the elf's attributes using the default values from his race (or a average of different races, if you want...)
Some people may suggest making an OOP class with lots of named fields. This can also work, but IMHO a prototype model is better - it gives you much more flexibility in the long run. You often want to process large groups of attributes in the some way, and doing this is pretty messy if you have to refer to each of the attribute fields individually.

import java.util.ArrayList;
import java.util.List;
public class Race
{
private final int raceID;
private final double purity;
private final int strMod;
private final int dexMod;
private final int conMod;
private final int wisMod;
public Race (int raceID, double purity, int strMod, int dexMod, int conMod, int wisMod)
{
this.raceID = raceID;
this.purity = purity;
this.strMod = strMod;
this.dexMod = dexMod;
this.conMod = conMod;
this.wisMod = wisMod;
}
public int getRaceID ()
{
return raceID;
}
public double getPurity ()
{
return purity;
}
public int getStrMod ()
{
return strMod;
}
public int getDexMod ()
{
return dexMod;
}
public int getConMod ()
{
return conMod;
}
public int getWisMod ()
{
return wisMod;
}
#Override public String toString ()
{
return "RaceID:" + raceID
+ " purity:" + purity
+ " strMod:" + strMod
+ " dexMod:" + dexMod
+ " conMod:" + conMod
+ " wisMod:" + wisMod;
}
#override public int hashCode ()
{
return raceID;
}
#override public boolean equals (Race r)
{
return (r != null && this.raceID == r.getRaceID());
}
#override public Object clone ()
{
return new Race(this.raceID,this.purity,this.strMod,this.dexMod,this.conMod,this.wisMod);
}
public static void main(String args[])
{
// simple test
ArrayList<Race> races = new ArrayList<Race>();
Race a = new Race(0,0.5,1,2,3,4);
Race b = new Race(1,0.75,2,3,4,5);
Race c = new Race(2,0.25,-1,-2,-3,-4);
races.add(a);
races.add(b);
races.add(c);
for(Race race : races)
{
// System.out.println(race.toString());
System.out.println(race);
}
}
}
Then we have the visual model, which can be handled like this:
class RacePanel implements ActionListener
{
private Map<Integer,JToggleButton> r;
private Map<Integer,Race> f;
public RacePanel()
{
r = new TreeMap<Integer,JToggleButton>();
f = new TreeMap<Integer,Race>();
}
public JToggleButton add (Race a)
{
JToggleButton button = new JToggleButton();
button.setIcon(RCiconSM);
button.setBorder(BorderFactory.createEmptyBorder());
button.setContentAreaFilled(false);
button.setActionCommand(a.getRaceID());
button.addActionListener(this);
r.put(a.getRaceID, button);
f.put(a.getRaceID, a);
}
public void remove (int raceID)
{
r.remove(a.getRaceID);
f.remove(a.getRaceID);
}
// When a button is clicked
public void actionPerformed(ActionEvent e)
{
// related race
Race a = f.get(e.getActionCommand());
// clicked button
JToggleButton b = r.get(e.getActionCommand());
// ..
}
public ArrayList<JToggleButton> getButtonList ()
{
return new ArrayList<Value>(r.values());
}
public ArrayList<Race> getRaceList ()
{
return new ArrayList<Value>(f.values());
}
public Race getRace (int raceID)
{
return f.get(raceID);
}
public JToggleButton getButton (int raceID)
{
return r.get(raceID);
}
// ..
}