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Can't access the object within the GraphNode

I have a graph that contains objects of type GraphNodes. These nodes contain an object City that has properties if It's infected or not. I want to loop through all the nodes and check if a city is infected or not. I have a generic method getInfo which returns an object of type E in my case City. But when i try to chain another method or to get property i can't see them as if they are not available. All the classes in the code are from college so i can't add/remove methods. I've tried with foreach but I still can't get the methods.
Code:
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.util.LinkedList;
import java.util.Stack;
import java.util.StringTokenizer;
import java.util.LinkedList;
class City {
String osnovna_granka;
boolean zarazen;
City(String osnovna_granka, boolean zarazen) {
this.osnovna_granka = osnovna_granka;
this.zarazen = zarazen;
}
#Override
public String toString() {
if (zarazen == true) {
return osnovna_granka + " zarazen";
} else {
return osnovna_granka + " nezarazen";
}
}
}
class Graph {
int num_nodes;
GraphNode<City> adjList[];
#SuppressWarnings("unchecked")
public Graph(int num_nodes) {
this.num_nodes = num_nodes;
adjList = (GraphNode<City>[]) new GraphNode[num_nodes];
}
int adjacent(int x, int y) {
// proveruva dali ima vrska od jazelot so
// indeks x do jazelot so indeks y
return (adjList[x].containsNeighbor(adjList[y])) ? 1 : 0;
}
void addEdge(int x, int y) {
// dodava vrska od jazelot so indeks x do jazelot so indeks y
if (!adjList[x].containsNeighbor(adjList[y])) {
adjList[x].addNeighbor(adjList[y]);
}
}
void deleteEdge(int x, int y) {
adjList[x].removeNeighbor(adjList[y]);
}
#Override
public String toString() {
String ret = new String();
for (int i = 0; i < this.num_nodes; i++) {
ret += i + ": " + adjList[i] + "\n";
}
return ret;
}
}
class GraphNode<E> {
private int index;//index (reden broj) na temeto vo grafot
private E info;
private LinkedList<GraphNode<E>> neighbors;
public GraphNode(int index, E info) {
this.index = index;
this.info = info;
neighbors = new LinkedList<GraphNode<E>>();
}
boolean containsNeighbor(GraphNode<E> o) {
return neighbors.contains(o);
}
void addNeighbor(GraphNode<E> o) {
neighbors.add(o);
}
void removeNeighbor(GraphNode<E> o) {
if (neighbors.contains(o)) {
neighbors.remove(o);
}
}
#Override
public String toString() {
String ret = "INFO:" + info + " SOSEDI:";
for (int i = 0; i < neighbors.size(); i++) {
ret += neighbors.get(i).info + " ";
}
return ret;
}
#Override
public boolean equals(Object obj) {
#SuppressWarnings("unchecked")
GraphNode<E> pom = (GraphNode<E>) obj;
return (pom.info.equals(this.info));
}
public int getIndex() {
return index;
}
public void setIndex(int index) {
this.index = index;
}
public E getInfo() {
return info;
}
public void setInfo(E info) {
this.info = info;
}
public LinkedList<GraphNode<E>> getNeighbors() {
return neighbors;
}
public void setNeighbors(LinkedList<GraphNode<E>> neighbors) {
this.neighbors = neighbors;
}
}
public class Main {
public static void main(String[] args) throws Exception {
int i, j, k;
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
int N = Integer.parseInt(br.readLine());
Graph g = new Graph(N);
for (i = 0; i < N; i++) {
StringTokenizer st = new StringTokenizer(br.readLine());
st.nextToken();
String osnovna_granka = st.nextToken();
String str_zarazen = st.nextToken();
if (str_zarazen.equals("zarazen")) {
g.adjList[i] = new GraphNode(i, new City(osnovna_granka, true));
} else {
g.adjList[i] = new GraphNode(i, new City(osnovna_granka, false));
}
}
int M = Integer.parseInt(br.readLine());
for (i = 0; i < M; i++) {
StringTokenizer st = new StringTokenizer(br.readLine());
int a = Integer.parseInt(st.nextToken());
int b = Integer.parseInt(st.nextToken());
g.addEdge(a, b);
g.addEdge(b, a);
}
br.close();
Stack<GraphNode> stack = new Stack<>();
int counter = 0;
// vasiot kod ovde;
for(GraphNode gn: g.adjList) {
gn.getInfo().// Here the properties of City should show up
}
}
}

GraphNode is a generic type and you have not specified the type, the IDE cannot infer the type so no methods can be suggested. in the for loop you need to specify the type of the GraphNode.
for(GraphNode<City> gn: g.adjList)

RPG game code error [duplicate]

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 5 years ago.
I keep getting this error in my code. Can someone fix it and how is the code written? Can it be improved by maybe using setters and getters only?
Exception in thread "main" java.lang.NullPointerException
at Player.attack(Player.java:72)
at Main.main(Main.java:15)
My code:
Player.java
public class Player {
String name;
String race;
int hp;
int power;
int armour;
Weapon weapon;
public Player (String n, String r, int h, int p, int a) {
name = n;
race =r;
hp = h;
power = p;
armour = a;
}
public void setName (String n) {
name = n;
}
public String getName() {
return name;
}
public void setRace (String r) {
race = r;
}
public String getRace() {
return race;
}
public void setHP (int h) {
hp = h;
}
public int getHP() {
return hp;
}
public void setPower (int p) {
power = p;
}
public int getPower() {
return power;
}
public void setArmour (int a) {
armour = a;
}
public int getArmour() {
return armour;
}
public boolean dead() {
return hp <= 0;
}
public boolean equip(Weapon weapon) {
this.weapon = weapon;
return true;
}
public boolean receiveDamage(int i) {
if ((hp - i) > 0) {
hp = hp - i;
return true;
}
hp = 0;
return false;
}
public boolean attack(Player player) {
return player.receiveDamage(weapon.useWeapon());
}
}
Main.java
public class Main {
public static void main(String args[]) {
Player Mensch = new Player("Mensch", "Mensch", 85, 12, 10);
Player Ork = new Player("Shrek", "Ork", 50, 14, 6);
Weapon MenschW = new Weapon("mächtiges Schwert", 15, 100);
Weapon OrkW = new Weapon("große Axt", 7, 100);
Mensch.equip(Mensch.weapon);
Ork.equip(Ork.weapon);
while (!Mensch.dead() && !Ork.dead() ) { //Alternativ: for (player hp >=0)
System.out.println("Mensch gegen Ork " + Mensch.attack(Ork));
if (Mensch.dead() || Ork.dead()) {
break;
}
System.out.println("Mensch gegen Ork " + Ork.attack(Mensch));
}
System.out.println("Ork ist tot: " + Ork.dead());
System.out.println("Mensch ist tot: " + Mensch.dead());
}
}
Weapon.java
import java.util.concurrent.ThreadLocalRandom;
public class Weapon {
String name;
int damage;
int hp;
public Weapon(String string, int d, int hp) {
// TODO Auto-generated constructor stub
}
public void setName (String n) {
name = n;
}
public String getName() {
return name;
}
public void setDamage (int d) {
damage = d;
}
public int getDamage() {
return damage;
}
public void setWHP (int h) {
hp = h;
}
public int getWHP() {
return hp;
}
public int useWeapon() {
if
(broken())
return 0;
hp = hp - 5;
return (damage / 2) + random();
}
private int random() {
return ThreadLocalRandom.current().nextInt(1, damage + 1);
}
private boolean broken() {
return hp <= 0;
}
}
I know its a lot of code but I keep getting the same error, also I'm quite new to java so I would appreciate some tips or suggestions to make my code better or more failsave. The code doesn't do much yet but it will (hopefully) be a simple game soon in which two characters fight eachother with some calculations on damageoutput of each player. In this case a Human and Ork. Feel free to try it out

Change
Mensch.equip(Mensch.weapon); // Mensch.weapon is not initialized in constructor so it is null.
Ork.equip(Ork.weapon); // Ork.weapon is not initialized in constructor so it is null as well.
To
// Use your newly created weapons in the main instead.
Mensch.equip(MenschW );
Ork.equip(OrkW);

Error with code for playlists in java mp3 player

I'm struggling with creating a playlist for my simple mp3 player in Java but the code is somehow not working. Here is the playlist part:
FileFilter filter = new FileNameExtensionFilter("MP3 Files", "mp3", "mpeg3");
JFileChooser chooser = new JFileChooser("C:\\Users\\Junior\\Music");
chooser.addChoosableFileFilter(filter);
chooser.setMultiSelectionEnabled(true);
int returnVal = chooser.showOpenDialog(null);
if(returnVal == JFileChooser.APPROVE_OPTION){
//File myFile=chooser.getSelectedFile();
File[] files=chooser.getSelectedFiles();
//String song=myFile+"";
for(int i=0; i<files.length;i++){
name=files[i].getName()+"";//getting song name for display purpose
try {
MC.Stop();//stopping if any file is playing
display.setText(name.substring(0,name.length()-4));//setting name songs in display (without .mp3)
MC.Play(files[i]+"");//from main class i'm calling play method
} catch (IOException e) {//i'm not really catching any exceptions so...
}//end of catch
}//end of for-loop
}//end of if
This code is playing the last song selected (even if I choose multiple files - so the last selected song) but not advancing to the next song.

I thought this might help you from reading your comment. This is a playlist class that I created. It's an abstract class, so you need to create your own class that extends this class, and implement the loadSongs method
public abstract class Playlist {
public static final int LOOP_NONE = 0;
public static final int LOOP_PLAYLIST = 1;
public static final int LOOP_SONG = 2;
private List<File> songs;
private int playlistPos;
private int loopMode;
private boolean isShuffled;
public Playlist() {
isShuffled = false;
loopMode = 0;
}
protected abstract List<File> loadPlaylist();
public void initPlaylist() {
songs = loadPlaylist();
}
public File getCurrentSong() {
return songs.get(playlistPos);
}
public int getPlaylistPosition() {
return playlistPos;
}
public void setPlaylistPosition(int playlistPos) {
this.playlistPos = playlistPos;
}
public int getPlaylistSize() {
return songs.size();
}
public boolean isFinalSong() {
return playlistPos == songs.size() - 1;
}
public boolean isShuffled() {
return isShuffled;
}
public int getLoopMode() {
return loopMode;
}
public void toggleShuffle() {
setShuffle(!isShuffled);
}
public void toggleLoop() {
loopMode = (loopMode + 1) % 3;
}
public void skipForward() {
playlistPos = (playlistPos + 1) % songs.size();
// Re-shuffle songs each time the playlist loops
if (playlistPos == 0 && isShuffled) {
shuffle();
}
}
public void skipBack() {
playlistPos = playlistPos == 0 ? songs.size() - 1 : playlistPos - 1;
}
public void setLoop(int loopMode) {
this.loopMode = loopMode;
}
public void setShuffle(boolean shuffle) {
this.isShuffled = shuffle;
if (isShuffled) {
shuffle();
}
else {
unshuffle();
}
}
protected void shuffle() {
Collections.shuffle(songs.subList(playlistPos + 1, songs.size()));
}
protected void unshuffle() {
initPlaylist();
}
}
So you would create a subclass like this:
public TestPlaylist extends Playlist {
#Override
protected List<File> loadPlaylist() {
// Show your file chooser, and return the selected files
// as a list.
}
}
And to use it, you would write:
Playlist playlist = new TestPlaylist();
playlist.initPlaylist();
// Do what you want with it, for example:
playlist.setShuffle(true);
MC.play(playlist.getCurrentSong().getAbsolutePath());

Java Serializable Saving

Well I have this class for a game I'm making, and I'm trying to save the ArrayList notes. When I logout, it properly print the size, for example if I have 5 notes, when I log out notes.getSize() would be 5, but when I log in, it gets reset back to nothing. Why isn't notes saving?
public class Notes implements Serializable {
private static final long serialVersionUID = -4947870743226160329L;
private ArrayList<Note> notes = new ArrayList<Note>(30);
public class Note implements Serializable {
private static final long serialVersionUID = -4589885080580317958L;
private int color = 0;
private String text = "";
public Note(int color, String text) {
this.setColor(color);
this.setText(text);
}
public void setText(String text) {
this.text = text;
}
public String getText() {
return text;
}
public void setColor(int color) {
this.color = color;
}
public int getColor() {
return color;
}
}
private transient Player player;
public Notes(Player p) {
this.player = p;
}
public void addNote(String text) {
System.out.println("Note Text: "+text);
if (text.length() > 50) {
player.getPackets().sendGameMessage("You can only enter notes up to 50 characters!");
return;
}
if (notes.size() < 30) {
notes.add(new Note(0, text));
} else {
player.getPackets().sendGameMessage("You cannot add more then 30 notes!");
return;
}
int NoteId = notes.size() - 1;
player.getPackets().sendConfig(1439, NoteId);
player.getTemporaryAttributtes().put("selectedNote", NoteId);
refreshNotes(false);
}
public void addNote(String text, int color) {
notes.add(new Note(color, text));
}
public void loadNotes() {
player.getPackets().sendIComponentSettings(34, 9, 0, 30, 2621470);
player.getPackets().sendHideIComponent(34, 3, false);
player.getPackets().sendHideIComponent(34, 44, false);
player.getPackets().sendIComponentText(34, 13, "Loading notes<br>Please wait...");
player.getPackets().sendConfig(1439, -1);
refreshNotes(true);
}
public void refreshNotes(boolean sendStartConfigs) {
for (int i = 0; i < 30; i++) {
player.getPackets().sendGlobalString(149 + i, i < notes.size() ? notes.get(i).getText() : "");
}
if (sendStartConfigs) {
for (int i = 1430; i < 1450; i++)
player.getPackets().sendConfig(i, i);
}
player.getPackets().sendConfig(1440, getFirstTotalColorValue());
player.getPackets().sendConfig(1441, getSecondTotalColorValue());
}
public int intColorValue(int color, int noteId) {
return (int) (Math.pow(4, noteId) * color);
}
public int getFirstTotalColorValue() {
int Color = 0;
for (int i = 0; i < 15; i++) {
if (notes.size() > i)
Color += intColorValue(notes.get(i).getColor(), i);
}
return Color;
}
public int getSecondTotalColorValue() {
int color = 0;
for (int i = 0; i < 15; i++) {
if (notes.size() > (i + 16))
color += intColorValue(notes.get(i + 16).getColor(), i);
}
return color;
}
public void deleteSelectedNote() {
if ((int)player.getTemporaryAttributtes().get("selectedNote") > -1) {
int slot = (int) player.getTemporaryAttributtes().get("selectedNote");
notes.remove(slot);
player.getTemporaryAttributtes().put("selectedNote", -1);
player.getPackets().sendConfig(1439, -1);
refreshNotes(false);
}
}
public void clear() {
notes.clear();
refreshNotes(false);
}
public void editNote(String string, int index) {
notes.get(index).setText(string);
refreshNotes(false);
}
public void setColor(int color, int index) {
notes.get(index).setColor(color);
refreshNotes(false);
}
public void deleteNote(int slot) {
notes.remove(slot);
refreshNotes(false);
}
public void setNotes(ArrayList<Note> setNotes) {
notes = setNotes;
refreshNotes(false);
}
}
And here is the class I manage saving/loading in
public class SerializableFilesManager {
private static final String PATH = "data/characters/";
private static final String BACKUP_PATH = "data/charactersBackup/";
public synchronized static final boolean containsPlayer(String username) {
return new File(PATH + username + ".p").exists();
}
public synchronized static Player loadPlayer(String username) {
try {
return (Player) loadSerializedFile(new File(PATH + username + ".p"));
} catch (Throwable e) {
Logger.handle(e);
}
try {
Logger.log("SerializableFilesManager", "Recovering account: "
+ username);
return (Player) loadSerializedFile(new File(BACKUP_PATH + username
+ ".p"));
} catch (Throwable e) {
Logger.handle(e);
}
return null;
}
public static boolean createBackup(String username) {
try {
Utils.copyFile(new File(PATH + username + ".p"), new File(
BACKUP_PATH + username + ".p"));
return true;
} catch (Throwable e) {
Logger.handle(e);
return false;
}
}
public synchronized static void savePlayer(Player player) {
try {
storeSerializableClass(player, new File(PATH + player.getUsername()
+ ".p"));
} catch (ConcurrentModificationException e) {
//happens because saving and logging out same time
} catch (Throwable e) {
Logger.handle(e);
}
}
public static final Object loadSerializedFile(File f) throws IOException,
ClassNotFoundException {
if (!f.exists())
return null;
ObjectInputStream in = new ObjectInputStream(new FileInputStream(f));
Object object = in.readObject();
in.close();
return object;
}
public static final void storeSerializableClass(Serializable o, File f)
throws IOException {
ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream(f));
out.writeObject(o);
out.close();
}
private SerializableFilesManager() {
}
}

Do NOT mark Player as transient, cause you are saving it, transient will prevent if from
getting saved, and will bring player to the default value of null, when deserialized.
Have you made the player class serializable ?
Its the Entire object graph that gets serialized or none... the purpose of transient is to make a particular member to be left off during serialization so that, the process of serialization goes smoothly.
For example, Suppose in a game we want to keep the progress of the player and hours of play for that session, but not the starting and ending times. So the starting and ending time can be made transient.

you should save your ArrayList with:
FileOutputStream fos = null;
ObjectOutputStream out = null;
try {
fos = new FileOutputStream("filename",false);
out = new ObjectOutputStream(fos);
out.writeObject(notes);
out.close();
System.out.println("Object Persisted");
} catch (IOException ex) {
ex.printStackTrace();
}
and when you open your project, import you Arraylist with:
FileInputStream fos;
try {
fos = new FileInputStream("filename");
ObjectInputStream oos = new ObjectInputStream(fos);
notes=(ArrayList) oos.readObject();
fos.close();
{
catch {
}

Thats because your Player is transient...I've tried to demonstrate your logic on other example...when Player was set to private, serialization has been successful and all data has been loaded back. Otherwise, when transient, Player reference was null, it loads only other serialized fields like int. When theres only a transient Player as field in class, the NullPointerException occurs, but ArrayList has size > 0.

transfer form one state to another

I use centralized patter to coding vending machine. The problem is I found out that I cannot change states. In the constructor, I initialized state to Ls[0], but when I go to the method public void coin() to change the state, I found that the state doesn't changed. The part of my code is:
class Vending_machine {
State st;
private int price;
private int k;
private int k1;
private int t;
private int s;
private State[] Ls;
public Vending_machine() {
Ls = new State[7];
Ls[0] = new Idle();
Ls[1] = new Coins_inserted();
Ls[2] = new Sugar();
Ls[3] = new No_small_cups();
Ls[4] = new No_large_cups();
Ls[5] = new Exit();
Ls[6] = new Start();
st = Ls[0];
st.vm = this;
k = 0;
k1 = 0;
t = 0;
price = 0;
s = 0;
}
public void setK(int k) {
this.k = k;
}
public int getK() {
return k;
}
public void setS(int s) {
this.s = s;
}
public int getS() {
return s;
}......
public void coin() {
st.coin();
if (st.getId() == 0) {
if (t + 25 < price) {
// t=t+25;
st = Ls[0];
}
if (t + 25 >= price && price > 0) {
// s=0;
// t=0;
st = Ls[1];
}
}......
class State {
public Vending_machine vm;
int id = 0;
public void coin() {}
public void small_cup() {}
public void large_cup() {}
public void sugar() {}
public void tea() {}
public void insert_large_cups(int n) {}
public void insert_small_cups(int n) {}
public void set_price(int p) {}
.......
}
class Idle extends State {
public void coin() {
if (vm.getT() + 25 < vm.getPrice()) {
vm.setT((vm.getT()) + 25);
System.out.println(vm.getT());
}
else if ((vm.getT() + 25 >= vm.getPrice()) && (vm.getPrice() > 0)) {
vm.setS(0);
vm.setT(0);
}
}......