我正在上课这件事，我和Jlists一直有很多麻烦。我以为我终于想出了如何用列表数据模型更新它们，但它仍然不起作用。
请帮忙。
上课给我带来麻烦：
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
import java.util.*;
import java.lang.*;
public class ClubDriverWindow extends JPanel implements ActionListener{
private ArrayList playerList;
private DefaultListModel playerListModel;
private String[] secondPlayerItems = new String[1];
private String[] firstPlayerItems = new String[1];
private String[] players1Items = new String[1];
private String[] players2Items = new String[1];
private String[] retirePlayerItems = new String[1];
private String[] jcomp12Items = new String[1];
private String[] restorePlayerItems = new String[1];
private JTextArea players;
private JComboBox secondPlayer;
private JComboBox firstPlayer;
private JButton player1Win;
private JButton player2wins;
private JButton draw;
private JButton exit;
private JComboBox players1;
private JComboBox players2;
private JTextArea jcomp10;
private JComboBox retirePlayer;
private JList jcomp12;
private JComboBox restorePlayer;
private JButton retireButton;
private JButton restoreButton;
private JTextArea jcomp16;
private JTextField addPlayer;
private JButton addButton;
public ClubDriverWindow() {
playerList = new ArrayList<Player>();
Player starter = new Player ("Starter");
playerList.add(starter);
playerList.add(starter);
playerList.add(starter);
playerList.add(starter);
playerList.add(starter);
playerListModel = new DefaultListModel<String>();
updatePlayers();
//construct components
players = new JTextArea (5, 5);
secondPlayer = new JComboBox (secondPlayerItems);
secondPlayer.addActionListener(this);
secondPlayer.setActionCommand("secondPlayerComboBox");
firstPlayer = new JComboBox (firstPlayerItems);
player1Win = new JButton ("Win");
player2wins = new JButton ("Win");
draw = new JButton ("Draw");
exit = new JButton ("Exit");
exit.addActionListener(this);;
exit.setActionCommand("exit");
players1 = new JComboBox (players1Items);
players2 = new JComboBox (players2Items);
jcomp10 = new JTextArea (5, 5);
retirePlayer = new JComboBox (retirePlayerItems);
jcomp12 = new JList (playerListModel);
restorePlayer = new JComboBox (restorePlayerItems);
retireButton = new JButton ("Retire");
restoreButton = new JButton ("Restore");
jcomp16 = new JTextArea (5, 5);
addPlayer = new JTextField (5);
addButton = new JButton ("Add Player");
addButton.addActionListener(this);
addButton.setActionCommand("addPlayer");
//set components properties
players.setToolTipText ("This is a leaderboard of players");
secondPlayer.setToolTipText ("Choose a Player");
firstPlayer.setToolTipText ("Choose a player");
player1Win.setToolTipText ("Player 1 wins");
player2wins.setToolTipText ("Player2 Wins");
draw.setToolTipText ("No victor");
exit.setToolTipText ("Help, I am trapped in a JButton!");
players1.setToolTipText ("Choose a Player");
players2.setToolTipText ("Choose a Player");
retirePlayer.setToolTipText ("CHoose a Player");
restorePlayer.setToolTipText ("Choose a player");
retireButton.setToolTipText ("Set a player aside (for now)");
restoreButton.setToolTipText ("Click here to bring a player back");
addButton.setToolTipText ("Click here to add a new player");
//adjust size and set layout
setPreferredSize (new Dimension (784, 508));
setLayout (null);
//add components
add (players);
add (secondPlayer);
add (firstPlayer);
add (player1Win);
add (player2wins);
add (draw);
add (exit);
add (players1);
add (players2);
add (jcomp10);
add (retirePlayer);
add (jcomp12);
add (restorePlayer);
add (retireButton);
add (restoreButton);
add (jcomp16);
add (addPlayer);
add (addButton);
//set component bounds (only needed by Absolute Positioning)
players.setBounds (40, 40, 300, 300);
secondPlayer.setBounds (-170, 295, 100, 75);
firstPlayer.setBounds (-185, 355, 100, 75);
player1Win.setBounds (45, 405, 100, 25);
player2wins.setBounds (215, 405, 100, 25);
draw.setBounds (135, 445, 100, 25);
exit.setBounds (675, 5, 100, 25);
players1.setBounds (45, 365, 100, 25);
players2.setBounds (215, 365, 100, 25);
jcomp10.setBounds (380, 0, 2, 600);
retirePlayer.setBounds (415, 60, 100, 25);
jcomp12.setBounds (-150, 345, 100, 75);
restorePlayer.setBounds (415, 110, 100, 25);
retireButton.setBounds (595, 60, 100, 25);
restoreButton.setBounds (595, 110, 100, 25);
jcomp16.setBounds (-150, 300, 100, 75);
addPlayer.setBounds (415, 165, 100, 25);
addButton.setBounds (595, 165, 100, 25);
}
public static void main (String[] args) {
JFrame frame = new JFrame ("MyPanel");
frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add (new ClubDriverWindow());
frame.pack();
frame.setVisible (true);
}
public void wonGame(Player winner, Player loser){
double wRating = winner.getRating();
double lRating = loser.getRating();
double pointModifier = (lRating/wRating);
wRating += ((pointModifier*10)+0.5);
lRating -= ((pointModifier*10)-0.5);
winner.setRating(wRating);
loser.setRating(lRating);
winner.setWins(winner.getWins() + 1);
loser.setLosses(winner.getLosses() + 1);
}
public void drawGame(Player player1, Player player2){
double p1Rating = player1.getRating();
double p2Rating = player2.getRating();
double p1modifier = ((p1Rating-p2Rating)/p1Rating);
double p2modifier = ((p2Rating-p1Rating)/p2Rating);
p1Rating += ((p1modifier*-5));
p2Rating += ((p2modifier*-5));
player1.setRating(p1Rating);
player2.setRating(p2Rating);
player1.setDraws(player1.getDraws() + 1);
player2.setDraws(player2.getDraws() + 1);
}
public void actionPerformed(ActionEvent e){
if (e.getActionCommand().equals("secondPlayerComboBox")){
}
else if (e.getActionCommand().equals("exit")){
System.exit(0);
}
else if (e.getActionCommand().equals("addPlayer")){
addNewPlayer();
}
}
public void addNewPlayer(){
}
public void updatePlayers(){
int size = playerList.size();
playerListModel.clear();
for (int j = 0; (j < (size-1)); j++){
playerListModel.add(j,((Player)playerList.get(j)).getName());
}
jcomp12.setModel(playerListModel);
}
}
相关玩家类：
public class Player
{
//private Record playerRecord
private double rating;
private final String ID = "";
private int ranking;
public String name;
private int losses;
private int wins;
private int draws;
public Player(String name){
rating = 1000.0;
ranking = 0;
name = name;
losses = 0;
wins = 0;
draws = 0;
}
int getTotalGames(){
int t = (wins+draws+losses);
return t;
}
float getWinLossRatio(){
float r = (wins/losses);
return r;
}
int getWins(){
return wins;
}
int getLosses(){
return losses;
}
int getDraws(){
return draws;
}
double getRating(){
return rating;
}
String getID(){
return ID ;
}
double getRanking(){
return ranking;
}
String getName(){
return name;
}
void setWins(int newWins){
wins = newWins;
}
void setLosses(int newLosses){
losses = newLosses;
}
void setDraws(int newDraws){
draws = newDraws;
}
void setRating(double newRating){
rating = newRating;
}
void setName(String newName){
name = newName;
}
}
错误：
java.lang.NullPointerException
at ClubDriverWindow.updatePlayers(ClubDriverWindow.java:194)
at ClubDriverWindow.<init>(ClubDriverWindow.java:52)
at ClubDriverWindow.main(ClubDriverWindow.java:144)
请帮忙， 感谢。
答案 0 :(得分：5)
也许你应该改变
private ArrayList playerList;
private DefaultListModel playerListModel;
到
private ArrayList<Player> playerList;
private DefaultListModel<String> playerListModel;
对于这部分，
Player starter = new Player ("Starter");
playerList.add(starter);
playerList.add(starter);
playerList.add(starter);
playerList.add(starter);
playerList.add(starter);
如果你想要5个不同的Players，你需要逐个创建它们，例如
Player starter = null;
for(int i = 0; i < 5; i++) {
starter = new Player("Starter" + i);
playerList.add(starter);
}
好的，这是NullPointerException部分的答案。
对于NullPointerException，您需要在初始化updatePlayers();后致电jcomp12。
jcomp12 = new JList (playerListModel);
// ....
updatePlayers();
或jcomp12在updatePlayers()方法中为空！