JList不在JScrollPane中显示

Question

import java.awt.event.*;
import java.io.File;
import javax.swing.*;

public class Launch extends JFrame implements ActionListener {
private static final long serialVersionUID = 5291490384908841627L;
JButton OK, create;
JList<String> players;
File player;
public static void main(String[] args) {
    new Launch();
}
private Launch() {
    this.setSize(600, 600);
    this.setLocationRelativeTo(null);
    this.setTitle("A Word Game");
    this.setDefaultCloseOperation(EXIT_ON_CLOSE);
    Box box = Box.createVerticalBox();
    OK = new JButton("OK");
    create = new JButton("Create new player");
    OK.addActionListener(this);
    create.addActionListener(this);
    String[] playerList = getPlayers();
    players = new JList<String>(playerList);
    players.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
    JScrollPane scroll = new JScrollPane(players, JScrollPane.VERTICAL_SCROLLBAR_ALWAYS, JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);
    scroll.add(players);
    final JLabel choosePrompt = new JLabel("Choose a player.");
    box.add(Box.createVerticalStrut(20));
    box.add(choosePrompt);
    box.add(Box.createVerticalStrut(20));
    box.add(scroll);
    box.add(Box.createVerticalStrut(20));
    box.add(OK);
    box.add(Box.createVerticalStrut(20));
    box.add(create);
    box.add(Box.createVerticalStrut(20));
    this.add(box);
    this.setVisible(true);
}
private String[] getPlayers() {
    File playerDirectory = new File("players");
    File[] playersInFiles = playerDirectory.listFiles();
    String[] players = new String[playersInFiles.length];
    for (int counter = 0; counter < playersInFiles.length; counter ++) {
        players[counter] = trimTXT(playersInFiles[counter].getName());
    }
    return players;
}
private String trimTXT(String original) {
    return original.substring(0, original.length() - 4);
}
@Override
public void actionPerformed(ActionEvent e) {
    if (e.getSource().equals(OK)) {
        String name = players.getSelectedValue();
        if (name == null) {
            return;
        }
        player = new File(name + ".txt");
    } else if (e.getSource().equals(create)) {
        //create a new character, all that what-not
    }
}
}

The problem is that the players don't show up in the JScrollPane. The scroll pane is just there without anything inside it. I have a bunch of blank .txt files representing players in the players folder. They are just for testing. The weid thing is that when the JList is not in the JScrollPane, it works fine. When I add it to a JScrollPane, then the stuff inside doesn't show up.

Answer 1

import java.awt.event.*;
import java.io.File;
import javax.swing.*;

public class Launch extends JFrame implements ActionListener {
private static final long serialVersionUID = 5291490384908841627L;
JButton OK, create;
JList players;
File player;
public static void main(String[] args) {
    new Launch();
}
private Launch() {
    // don't do this
    this.setSize(600, 600);
    this.setLocationRelativeTo(null);
    this.setTitle("A Word Game");
    this.setDefaultCloseOperation(EXIT_ON_CLOSE);
    Box box = Box.createVerticalBox();
    OK = new JButton("OK");
    create = new JButton("Create new player");
    OK.addActionListener(this);
    create.addActionListener(this);
    String[] playerList = getPlayers();
    players = new JList(playerList);
    players.setSelectionMode(ListSelectionModel.SINGLE_SELECTION);
    JScrollPane scroll = new JScrollPane(players, JScrollPane.VERTICAL_SCROLLBAR_ALWAYS, JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);
    //scroll.add(players);
    final JLabel choosePrompt = new JLabel("Choose a player.");
    box.add(Box.createVerticalStrut(20));
    box.add(choosePrompt);
    box.add(Box.createVerticalStrut(20));
    box.add(scroll);
    box.add(Box.createVerticalStrut(20));
    box.add(OK);
    box.add(Box.createVerticalStrut(20));
    box.add(create);
    box.add(Box.createVerticalStrut(20));
    this.add(box);
    pack();
    this.setVisible(true);
}
private String[] getPlayers() {
    /*File playerDirectory = new File("players");
    File[] playersInFiles = playerDirectory.listFiles();
    String[] players = new String[playersInFiles.length];
    for (int counter = 0; counter < playersInFiles.length; counter ++) {
        players[counter] = trimTXT(playersInFiles[counter].getName());
    }*/
    String[] players = {"Bob", "Jane"};
    return players;
}
private String trimTXT(String original) {
    return original.substring(0, original.length() - 4);
}
@Override
public void actionPerformed(ActionEvent e) {
    if (e.getSource().equals(OK)) {
        String name = (String)players.getSelectedValue();
        if (name == null) {
            return;
        }
        player = new File(name + ".txt");
    } else if (e.getSource().equals(create)) {
        //create a new character, all that what-not
    }
}
}

Answer 2

错误是

 scroll.add(players)