swing - Image filepath in Java GUI - NullPointerException -
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- what nullpointerexception, , how fix it? 12 answers
i making simple card game , i'm trying use file paths .jpg files card images. getting nullpointerexception, new java , struggling understand means , for.
this output:
tie. error in nextcard computer wins! error in nextcard exception in thread "awt-eventqueue-0" java.lang.nullpointerexception @ war.getplayercard(war.java:160) @ wargui$playcardlistener.actionperformed(wargui.java:98) i have traced far:
war class:
public string getplayercard() { return playerwarcard.getfilepath(); // error } called wargui:
playercard = new imageicon(game.getplayercard()); // error i have feeling problem getfilepath method in card class (marked @ bottom), i'm unsure , appreciate if confirm.
card class:
public class card { // suits private int suit; public final static int spades = 1; public final static int hearts = 2; public final static int diamonds = 3; public final static int clubs = 4; // ranks private int rank; public final static int jack = 11; public final static int queen = 12; public final static int king = 13; public final static int ace = 14; string cardfilepath; /** constructor initializes card's rank , suit. @param rank @param suit */ public card(int rank, int suit) { this.rank = rank; this.suit = suit; cardfilepath = "cardpics/" + suit + rank + ".jpg"; } /** other constructor initializes card's rank , suit. @param othercard copied */ public card(card othercard) { this.rank = othercard.rank; this.suit = othercard.suit; } /** getrank method returns int represents card's rank. @return card's rank */ public int getsuit() { return suit; } /** getrank method returns int represents card's rank. @return card's rank */ public int getrank() { return rank; } /** * returns description of card. * @return name of card. */ public string tostring() { return getrankasstring() + " of " + getsuitasstring(); } /** equals method compares rank of card rank of card. if same, method returns true. @return boolean */ public boolean equals(card othercard ) { return rank == othercard.rank; } /** getsuitstring method returns card's suit string. @return suitstring */ public string getsuitasstring() { switch (suit) { case spades: return "spades"; case hearts: return "hearts"; case diamonds: return "diamonds"; case clubs: return "clubs"; default: return "invalid"; } } /** getrankstring method returns card's rank. @return rank */ public string getrankasstring() { switch (rank) { case 2: return "2"; case 3: return "3"; case 4: return "4"; case 5: return "5"; case 6: return "6"; case 7: return "7"; case 8: return "8"; case 9: return "9"; case 10: return "10"; case 11: return "jack"; case 12: return "queen"; case 13: return "king"; case 14: return "ace"; default: return "??"; } } /** returns .jpg image of card @return path image */ public string getfilepath() // error? { return cardfilepath; } } attached reference war class:
import java.util.arraylist; import javax.swing.*; public class war { static cardpile warpile; static cardpile player1 = new cardpile(); static cardpile player2 = new cardpile(); static card unseenplayercard; static card unseencomputercard; static card playerwarcard; static card computerwarcard; static string war = "false"; /** constructor prepares, shuffles deck deals players. */ public void war() { deck deck = new deck(); deck.shuffle(); while(deck.getsize() > 0) { player1.collectcard(deck.deal()); player2.collectcard(deck.deal()); } } /** comparecards method compares rank of card determine winner @param playerscard, computerscard @return outcome */ public static int comparecards(card playerscard, card computerscard) { if (playerscard.getrank() > computerscard.getrank()) { player1.collectcard(playerscard); player1.collectcard(computerscard); system.out.println("player's card: " + playerscard.tostring() + "\ncomputer's card: " + computerscard.tostring() + "\nyou win!"); return 1; } else if (playerscard.getrank() < computerscard.getrank()) { player2.collectcard(playerscard); player2.collectcard(computerscard); system.out.println("your card: " + playerscard.tostring() + "\ncomputer's card: " + computerscard.tostring() + "\nyou lose."); return 2; } // if cards equal, war else { war = "true"; system.out.println("your card: " + playerscard.tostring()); system.out.println("computer's card: " + computerscard.tostring()); joptionpane.showmessagedialog(null, "war!"); beginwar(playerscard, computerscard); return 3; } } /** beginwar method draws war cards, compares determine winner of war. @param playerscard, computerscard */ public static void beginwar(card playerscard, card computerscard) { // prize cards unseenplayercard = player1.playcard(); unseencomputercard = player2.playcard(); // add cards winning pile warpile.collectcard(playerscard); warpile.collectcard(computerscard); warpile.collectcard(unseenplayercard); warpile.collectcard(unseencomputercard); // determine winner playerwarcard = player1.playcard(); computerwarcard = player2.playcard(); int outcome = comparecards(playerwarcard, computerwarcard); if (outcome == '1') { system.out.println("you win war!"); } if (outcome == '2') { system.out.println("you lose war."); } } /** computercardsleft method returns number of cards in computer's hand. @return computer hand size */ public int computercardsleft() { return player2.getsize(); } /** playercardsleft method returns number of cards in players's hand. @return player hand size */ public int playercardsleft() { return player1.getsize(); } /** getcomputercard method returns image path of computer's card gui. @return filepath */ public string getcomputercard() { return computerwarcard.getfilepath(); } /** getplayercard method returns image path of computer's card gui. @return filepath */ public string getplayercard() { return playerwarcard.getfilepath(); // error } /** playerdraw method draws next card in player's pile. @return card */ public card playerdraw() { if (player1.getsize() < 1) { endgame(); } return player1.nextcard(); } /** computerdraw method draws next card in computer's pile. */ public card computerdraw() { if (player2.getsize() < 1) { endgame(); } return player2.playcard(); } /** endgame method displays results. */ public void endgame() { if (player1.getsize() > player2.getsize()) system.out.println("player wins!"); else if (player2.getsize() > player1.getsize()) system.out.println("computer wins!"); else system.out.println("tie."); } /** enoughcards method determins whether or not player meets minimum card requirement. */ public static boolean enoughcards(int n) { if (player1.getsize() < n || player2.getsize() < n) { return false; } return true; } } ...and wargui
import javax.swing.*; import java.awt.*; import java.awt.event.*; public class wargui extends jframe { private wargui guigame; private war game; private jpanel rightplayerpanel; // player private jpanel leftplayerpanel; // computer private jpanel buttonpanel; // holds buttons private jpanel gamepanel; // main deck area private jbutton playbutton; private static jlabel backlabelleft; private static jlabel playercardlabel; private static jlabel computercardlabel; private imageicon back; // icon backside of card private imageicon blank; // place holder private static imageicon playercard; // player 1's current card private static imageicon computercard; // player 2's current card private jtextfield playercardsleft; private jtextfield computercardsleft; // static hand player1; // static hand player2; private card playerscard; card computerscard; private string war = "false"; string imagepath = "cardpics/back.jpg"; /** constructor builds & adds panels contentpane. */ public wargui() { // set contentpane setlayout(new borderlayout()); settitle("game of war"); setsize(1100, 550); setdefaultcloseoperation(windowconstants.exit_on_close); setlocationrelativeto(null); // build & add deck panel assemblegamepanel(); add(gamepanel, borderlayout.center); // build & add player panels assembledeckspanel(); add(leftplayerpanel, borderlayout.west); add(rightplayerpanel, borderlayout.east); // build & add button panel assemblebuttonpanel(); add(buttonpanel, borderlayout.south); setvisible(true); // prepare deck & player hands game = new war(); // //welcome message // joptionpane.showmessagedialog(null, "welcome!"); } /** playcardlistener tracks clicks on play card button. cards drawn, war status checked, scores , images adjusted. */ private class playcardlistener implements actionlistener { public void actionperformed(actionevent e) { // regular gameplay if (war.equals("false")) { card playerscard = game.playerdraw(); card computerscard = game.computerdraw(); // update card images playercard = new imageicon(game.getplayercard()); // error playercardlabel.seticon(playercard); computercard = new imageicon(computerscard.getfilepath()); computercardlabel.seticon(computercard); // compare game.comparecards(playerscard, computerscard); // // otherwise, update score // //if (!war.equals("true")) // else // { // // playercardsleft.settext("player's cards: " + (player1.getsize() - 1)); // // computercardsleft.settext("computer's cards: " + (player2.getsize() - 1)); // // } playercardsleft.settext("player's cards: " + (game.playercardsleft() - 1)); computercardsleft.settext("computer's cards: " + (game.computercardsleft() - 1)); } // war deckplay // second click - face down card else if (war.equals("true")) { // set icons card backside playercardlabel.seticon(back); computercardlabel.seticon(back); war = "last"; } // third click else if (war.equals("last")) { // identify cards involved in war, update icons computercard = new imageicon(game.getcomputercard()); computercardlabel.seticon(computercard); playercard = new imageicon(game.getplayercard()); playercardlabel.seticon(playercard); war = "final"; } // war final else if (war.equals("final")) { war = "false"; // update scores playercardsleft.settext("player's cards: " + (game.playercardsleft())); computercardsleft.settext("computer's cards: " + (game.computercardsleft())); } else system.out.println("error"); } } /** assemblegamepanel builds cardpanel - main deck area, cards displayed. */ private void assemblegamepanel() { // place holder cards blank = new imageicon(); playercardlabel = new jlabel(blank); computercardlabel = new jlabel(blank); // add labels cardpanel gamepanel = new jpanel(); gamepanel.add(playercardlabel); gamepanel.add(computercardlabel); gamepanel.setpreferredsize(new dimension(545, 540)); gamepanel.setbackground(new color(0, 64, 0)); } /** assembledeckspanel method builds panel displays players' cardpiles. */ private void assembledeckspanel() { // icons of card backside = new imageicon(imagepath); // add icons backlabelleft = new jlabel(); backlabelleft.seticon(back); jlabel backlabelright = new jlabel(); backlabelright.seticon(back); // add labels panels // right rightplayerpanel = new jpanel(); rightplayerpanel.setpreferredsize(new dimension(150,220)); rightplayerpanel.add(backlabelright); rightplayerpanel.setbackground(new color(0, 64, 0)); playercardsleft = new jtextfield("player's cards: 26", 13); playercardsleft.seteditable(false); rightplayerpanel.add(playercardsleft); // left leftplayerpanel = new jpanel(); leftplayerpanel.setpreferredsize(new dimension(150,220)); leftplayerpanel.add(backlabelleft); leftplayerpanel.setbackground(new color(0, 64, 0)); computercardsleft = new jtextfield("computer's cards: 26", 13); computercardsleft.seteditable(false); leftplayerpanel.add(computercardsleft); } /** assemblebuttonpanel method adds buttons button panel. */ private void assemblebuttonpanel() { // create & add button jbutton playcardbutton = new jbutton("play!"); playcardbutton.setpreferredsize(new dimension(150,80)); buttonpanel = new jpanel(); buttonpanel.add(playcardbutton); buttonpanel.setbackground(new color(0, 64, 0)); // add event listeners buttons. playcardbutton.addactionlistener(new playcardlistener()); } /** main method begins gui deck. */ public static void main(string[] args) { wargui guigame = new wargui(); } } edit: understand there problem somewhere else. such, post other classes...
cardpile
public class cardpile { // create array hold player's pile, , parameters array. private card[] cardpile; private int front; private int end; /** constructor creates empty pile capable of holding 52 cards. */ public cardpile() { cardpile = new card[52]; front = 0; end = 0; } /** nextcard method returns card @ front of pile. @return c */ public card nextcard() { if (front == end) { system.out.println("error in nextcard"); } card c = cardpile[front]; front++; return c; } /** collectcard method adds card pile. */ public void collectcard(card c) { cardpile[end] = c; end++; } public card playcard() { return nextcard(); } /** getsize method returns size of pile. @return size */ public int getsize() { int size = end - front; return size; } /** clear method clears pile of cards. */ public void clear() { front = 0; end = 0; } } deck:
import java.util.*; public class deck { private card[] deck; private int numcards; /** constructor creates deck of 52 cards */ public deck() { deck = new card[52]; filldeck(); } /** filldeck method fills deck cards. */ public void filldeck() { int index = 0; (int q = 1; q <= 13; q++) { (int n = 1; n <= 4; n++) { deck[index] = new card(q, n); index++; } } } /** shuffle method shuffles deck. */ public void shuffle() { (int sh = 0; sh < numcards - 1; sh++) { int r = myrandom(sh, numcards - 1); card shufflecard = deck[sh]; deck[sh] = deck[r]; deck[r] = shufflecard; } } /** deal method deals players. @return updated deck */ public card deal() { if(numcards == 0) { return null; } numcards--; return deck[numcards]; } /** getsize method returns size of deck @return numcards in deck */ public int getsize() { return numcards; } /** myrandom method returns random number. @return random number */ private static int myrandom(int low, int high) { int random = (int)((high + 1 - low) * math.random() + low); return random; } }
you have 2 constructors:
public card(int rank, int suit) { this.rank = rank; this.suit = suit; cardfilepath = "cardpics/" + suit + rank + ".jpg"; } /** other constructor initializes card's rank , suit. @param othercard copied */ public card(card othercard) { this.rank = othercard.rank; this.suit = othercard.suit; } if card instantiated rank , suite, set cardfilepath. if instantiate using othercard never set cardfilepath, meaning instance no string created , cardfilepath = null.
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