How do I create a manager class to hold certain variables without abusing static?

Question

Java n00b here. I'm making a plugin for a Minecraft server, and I would like to use one class to hold all of the variables for the plugin:

public class BwMgr {

    Boolean enabled = false;

    final HashSet<Player> red = new HashSet<>();
    final HashSet<Player> green = new HashSet<>();
    final HashSet<Player> blue = new HashSet<>();
    final HashSet<Player> orange = new HashSet<>();
    final HashSet<Player> purple = new HashSet<>();
    final HashSet<Player> yellow = new HashSet<>();
    final HashSet<Player> black = new HashSet<>();
    final HashSet<Player> white = new HashSet<>();

    public void assignTeams() {

    }

}

Each HashSet is supposed to contain teams of players. The boolean will be accessed by other classes to determine whether the plugin is enabled or not:

public class BwListener implements Listener {

    private final BwMgr bwMgr = new BwMgr();

    @EventHandler
    public void onPlayerJoinEvent(PlayerJoinEvent e) {
        if (bwMgr.enabled) {
            // do stuff
        }
    }
}

enabled should be updated here:

public class BwCmd implements CommandExecutor {

    private BwMgr bwMgr = new BwMgr();

    @Override
    public boolean onCommand(CommandSender sender, Command cmd, String label, String[] args) {
        if (cmd.getName().equalsIgnoreCase("bw")) {
            if (args[0].equalsIgnoreCase("enable")) {
                bwMgr.enabled = true;             
            } else if (args[0].equalsIgnoreCase("disable")) {
                bwMgr.enabled = false;
            }
        }
        return false;
    }
}

Of course, since each class is using a different instance of BwMgr , they are using different versions of the Boolean enabled . I could just put static in front of everything in BwMgr but I feel like that would be abuse. Any ideas would be much appreciated.

Answer 1

You need to pass the same instance of BwMgr through the constructor of BwCmd and BwListener.

so in BwCmd should look like:

    public class BwCmd implements CommandExecutor {

    private BwMgr bwMgr;

    // Pass through the constructor an instance of BwMgr.
    public BwCmd(BwMgr bwMgr) {
        this.bwMgr = bwMgr;
    }
  
    @Override
    public boolean onCommand(CommandSender sender, Command cmd, String label, String[] args) {
        if (cmd.getName().equalsIgnoreCase("bw")) {
            if (args[0].equalsIgnoreCase("enable")) {
                bwMgr.enabled = true;             
            } else if (args[0].equalsIgnoreCase("disable")) {
                bwMgr.enabled = false;
            }
        }
        return false;
    }
}

BwListener class:

    public class BwListener implements Listener {

    private final BwMgr bwMgr;
    
    // Pass through the constructor an instance of BwMgr.
    public BwListener(BwMgr bwMgr) {
        this.bwMgr = bwMgr;
    }

    @EventHandler
    public void onPlayerJoinEvent(PlayerJoinEvent e) {
        if (bwMgr.enabled) {
            // do stuff
        }
    }
}

And in your main class:

// Create one instance of bwMgr.
BwMgr bwMgr = new BwMgr();

// Initialize BwListener and BwCmd with the same BwMgr.
BwListener bwListener = new BwListener(bwMgr);
BwCmd bwCmd = new BwCmd(bwMgr);