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

(identifier expected) getter/setter and objects

I've got a problem with my programm. When i try to compile following i just receive the message:
Tutorium.java:15: error: <identifier> expected
public void settName(vorlesung.lectureName) {
^
So my Code:
Tutorium.java
public class Tutorium {
private Vorlesung vorlesung;
public String tName;
private int tNumber;
public int gettNumber() {
return this.tNumber;
}
public String gettName() {
return this.tName;
}
public void settName(vorlesung.lectureName) {
this.tName = vorlesung.lectureName;
}
public String toString() {
return (this.tName + ", " + this.tNumber);
}
public Tutorium(int tNumber){
this.tNumber = tNumber; } }
Vorlesung.java
public class Vorlesung {
public String lectureName;
private int lectureNumber;
private int lecture;
private Dozent dozent;
private String lecturerlName;
public String getlectureName(){
return this.lectureName;
}
public int lectureNumber(){
return this.lectureNumber;
}
public int lecture(){
return this.lecture;
}
public String getlecturer(){
this.lecturerlName = dozent.lecturerlName;
return this.lecturerlName;
}
public String toString() {
return (this.lectureName + ", " + this.lectureNumber);
}
public Vorlesung(String lectureName, int lecture) {
this.lectureName = lectureName;
this.lecture = lecture +1;
this.lectureNumber = this.lecture -1;
this.lecturerlName = lecturerlName;
}}
My Main-Method:
public class MainVorlesung {
public static void main(String[] args) {
Student student = new Student("STUDENTNAME", "STUDENTLASTNAME", 178, 1);
Vorlesung vorlesung = new Vorlesung("Programmieren", 13341);
Tutorium tutorium = new Tutorium(3);
Dozent dozent = new Dozent("LECTURERFIRSTNAME", "LECTURERLASTNAME", 815);
System.out.println(student.toString());
System.out.println(vorlesung.toString());
System.out.println(tutorium.toString());
System.out.println(dozent.toString());
}}
My goal is to set the value of tName equal the value of vorlesung.lectureName.
Why can't i do this that way?
I appreciate every help. :)
Thanks

For methods, the arguments that you pass in must have a declared value.
In this case, a String. So you need to change your method to this:
public void settName(String newLectureName) {
this.tName = newLectureName;
}
Read more about what a java method is and how to create one here: http://www.tutorialspoint.com/java/java_methods.htm

Change settName to
public void settName(String name) {
this.tName = name;
}

Since your goal is:
My goal is to set the value of tName equal the value of vorlesung.lectureName.
You should get rid of the setName method entirely since it will depend entirely on the vorlesung field and so should not be changeable. You should also get rid of the tName field, and instead change getName() to:
public class Tutorium {
private Vorlesung vorlesung;
// public String tName; // get rid of
private int tNumber;
public String gettName() {
if (vorlesung != null) {
return vorlesung.getlecturer();
}
return null; // or throw exception
}
// *** get rid of this since you won't be setting names
// public void settName(Vorlesung vorlesung) {
// this.tName = vorlesung.lectureName;
// }
I have just now noticed that your Tutorium class does not have and absolutely needs a setVorlesung(...) method.
public void setVorlesung(Vorlesung vorlesung) {
this.vorlesung = vorlesung;
}

make a global object in java

I want to make an array of objects and use it in different functions. I wrote this pseudocode
privat stock[] d;
privat stock example;
public void StockCheck(){
d =new stock[2];
d[0]= new stock("a","test1", 22);
d[1]= new stock("b","test2", 34);
}
#Override
public stock getStock(String name) throws StockCheckNotFoundException{
int i;
System.out.println("ok" + name + d.legth); // error
example = new stock("example","example",2);
return example;
}
In class test I make an instance of getStock and I call the function getStock stock.getStock();
I get a NullPointerExeption when I do d.length. d is null but I don't understand why.

Hmmmm. If that is in any way like your real code, then the problem is that your "constructor" isn't really a constructor, as you've declared it to return void, making it an ordinary method instead. Remove tbat "void" and it may fix the problem!

Perhaps this example of code will do what you need, using three classes
Test - the main test code
Stock - the implied code for Stock from your question
StockCheck - the corrected code from your question.
(Note: you may really want to use an ArrayList inside StockQuote so you can add and delete Stocks.)
Test class
package stackJavaExample;
public class Test {
public static void main(String[] args) {
String[] testNames = {"test1","test2","notThere"};
StockCheck mStockCheck = new StockCheck();
for (int i=0; i<testNames.length; i++) {
Stock result = mStockCheck.getStock(testNames[i]);
if (result == null) {
System.out.println("No stock for name: " + testNames[i]);
} else {
System.out.println("Found stock: " + result.getName() + ", " + result.getSymbol() + ", " + result.getValue());
}
}
}
}
Stock class
package stackJavaExample;
public class Stock {
private String symbol;
private String name;
private double value;
public Stock(String symbol, String name, double value) {
this.symbol = symbol;
this.name = name;
this.value = value;
}
public String getSymbol() { return symbol;}
public String getName() { return name;}
public double getValue() {return value;}
}
StockCheck class
package stackJavaExample;
public class StockCheck {
private Stock[] d;
public StockCheck() {
d = new Stock[2];
d[0] = new Stock("a","test1", 22);
d[1] = new Stock("b","test2", 34);
}
public Stock getStock(String name) {
for (int i=0; i < d.length; i++) {
if (d[i].getName().equalsIgnoreCase(name)) {
return d[i];
}
}
return null;
}
}

toString, Nullpointerexception

I'm getting a Nullpointerexception when trying to get the trees name from the arraylist. I've tested just getting the name alone but i'm still getting this error. All i want to do is know which Equipment is cutting which tree.
public class TreeTester {
public static void main(String[] args) {
Tree trees = new Tree("Trees");
Tree tree1 = new Tree("Ash Tree");
trees.addTree(tree1);
Tree Class
public Class Tree{
private ArrayList<Tree> theTrees;
private String treeName;
//Forgot these
Tree(String trees //There are more but not relevent) {
theTrees = new ArrayList<Tree>();
}
Tree(String treeName){
this.treeName = treeName;
}
//
public boolean addTree(Tree newTree){
theTrees.add(newTree);
return true;
}
#Override
public String toString(){
String s = getTreeName();
return s;
}
private String getTreeName() {
return this.treeName; }
}
//------------------Shortened for ease--------------------------//
Just imagine the missing vars and contructor
public Class Equipment{
private Tree TreeDetails;
#Override
public String toString(){
String s = "Using " + getEqupiment(); + "to cut " + setCutTree()
}
public boolean setCutTree(){
this.treename = treename.toString(); //Nullpointer issue here
return this.treecut = true;
//getEquipment works fine
}
}

You need to intialize the theTrees ArrayList
public class Tree {
private ArrayList<Tree> theTrees = new ArrayList<Tree>();
You have also left out the one argument constructor of Tree that you are using in the main method. Since you are getting a NullPointerException even when accessing the name I assume this constructor does not initialize the treeName either.
With the constructor the class should look something like this:
public class Tree {
private ArrayList<Tree> theTrees;
private String treeName;
public Tree(String treeName) {
this.treeName = treeName;
this.theTrees = new ArrayList<Tree>();
}
...