Solved NullPointer when calling scoreboard between classes

So I am making a multi-class program to help me learn, and it is all going well except for the fact that I am getting this error. Here is the code:

Main Class (open) Main Class (close)

Code:

package me.flash110;

import java.util.ArrayList;

import org.bukkit.Bukkit;
import org.bukkit.ChatColor;
import org.bukkit.plugin.java.JavaPlugin;
import org.bukkit.scoreboard.Scoreboard;

public class SAM extends JavaPlugin {
    private static SAM instance;

    public SAM() {
        instance = this;
    }

    public static SAM getInstance() {
        return instance;
    }
   
    ArrayList<String> players = new ArrayList<>();
    Listeners listeners = new Listeners();
    Teams teams = Teams.getInstance();
    private Scoreboard scoreboard;
   
    public void onEnable() {
        Bukkit.getPluginManager().registerEvents(listeners, this);
        teams.initializeTeam("red", ChatColor.RED.toString());
       teams.initializeTeam("blue", ChatColor.BLUE.toString());
       getBoard();
    }
   
    public Scoreboard getBoard() {
        scoreboard = getServer().getScoreboardManager().getMainScoreboard();
        return scoreboard;
    }
}

Teams Class (open) Teams Class (close)

Code:

package me.flash110;

import org.bukkit.entity.Player;
import org.bukkit.scoreboard.Scoreboard;

public class Teams {
   
   
    //Constructor
    private static Teams instance;

    public Teams() {
        instance = this;
    }

    public static Teams getInstance() {
        return instance;
    }
   
   
    //The rest
    private Scoreboard scoreboard;
    SAM plugin = SAM.getInstance();
   
    public void initializeTeam(String teamName, String prefix) {
        scoreboard = plugin.getBoard();
           if (scoreboard.getTeam(teamName) == null) {
               scoreboard.registerNewTeam(teamName).setPrefix(prefix);
       }
    }
   
    @SuppressWarnings("deprecation")
    public void addTeam(Player p) {
        if (scoreboard.getTeam("red").getPlayers().size() < scoreboard.getTeam("blue").getPlayers().size()) {
            scoreboard.getTeam("red").addPlayer(p);
        }
        else {
            scoreboard.getTeam("blue").addPlayer(p);
        }
    }
}

NullPointer Error (open) NullPointer Error (close)

Code:

[21:13:53] [Server thread/INFO]: [SAM] Enabling SAM v1.0
[21:13:53] [Server thread/ERROR]: Error occurred while enabling SAM v1.0 (Is it up to date?)
java.lang.NullPointerException
    at me.flash110.SAM.onEnable(SAM.java:28) ~[?:?]
    at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:321) ~[craftbukkit.jar:git-Spigot-76236cb-9cd1111]
    at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:340) [craftbukkit.jar:git-Spigot-76236cb-9cd1111]
    at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:405) [craftbukkit.jar:git-Spigot-76236cb-9cd1111]
    at org.bukkit.craftbukkit.v1_8_R3.CraftServer.loadPlugin(CraftServer.java:357) [craftbukkit.jar:git-Spigot-76236cb-9cd1111]
    at org.bukkit.craftbukkit.v1_8_R3.CraftServer.enablePlugins(CraftServer.java:317) [craftbukkit.jar:git-Spigot-76236cb-9cd1111]
    at org.bukkit.craftbukkit.v1_8_R3.CraftServer.reload(CraftServer.java:741) [craftbukkit.jar:git-Spigot-76236cb-9cd1111]
    at org.bukkit.Bukkit.reload(Bukkit.java:535) [craftbukkit.jar:git-Spigot-76236cb-9cd1111]
    at org.bukkit.command.defaults.ReloadCommand.execute(ReloadCommand.java:25) [craftbukkit.jar:git-Spigot-76236cb-9cd1111]
    at org.bukkit.command.SimpleCommandMap.dispatch(SimpleCommandMap.java:141) [craftbukkit.jar:git-Spigot-76236cb-9cd1111]
    at org.bukkit.craftbukkit.v1_8_R3.CraftServer.dispatchCommand(CraftServer.java:641) [craftbukkit.jar:git-Spigot-76236cb-9cd1111]
    at org.bukkit.craftbukkit.v1_8_R3.CraftServer.dispatchServerCommand(CraftServer.java:627) [craftbukkit.jar:git-Spigot-76236cb-9cd1111]
    at net.minecraft.server.v1_8_R3.DedicatedServer.aO(DedicatedServer.java:412) [craftbukkit.jar:git-Spigot-76236cb-9cd1111]
    at net.minecraft.server.v1_8_R3.DedicatedServer.B(DedicatedServer.java:375) [craftbukkit.jar:git-Spigot-76236cb-9cd1111]
    at net.minecraft.server.v1_8_R3.MinecraftServer.A(MinecraftServer.java:653) [craftbukkit.jar:git-Spigot-76236cb-9cd1111]
    at net.minecraft.server.v1_8_R3.MinecraftServer.run(MinecraftServer.java:556) [craftbukkit.jar:git-Spigot-76236cb-9cd1111]
    at java.lang.Thread.run(Unknown Source) [?:1.8.0_91]
[21:13:53]

If you find anything that could be causing it then let me know.
And one more thing, please do not respond with; "Put it all in one class", or "learn java".
Other than that have a nice day/night!

 

@flash110

Learning Java is a very good idea though, it would help you diagnose this issue quite quickly. Your issue is that you've implemented the singleton design anti-pattern incorrectly, and Teams.getInstance() is returning null. Look up how to properly make a singleton and you will realise your issue.

 

@mythbusterma I only said the "learn Java" thing, because people decide to just type that and be done with the post. I have taken a Java course and have 2 books on Java. I was trying this to figure out the different ways to structure multi-class Java programs. It is late now and I will look into it tomorrow, thanks for the help though! (Sorry if I came across rude, wasn't trying to be)
EDIT:
I looked into it a little bit just now and found this bit

Code:

 

public class Class1 {
    private Main instance;

    public Class1(Main instance) {
        this.instance = instance;
    }

    public void doSomething() {
        instance.doSomethingElse();
    }
}

I will mess around with this more tomorrow, I edited this so you can see and let me know if this is the right way to do it.

 

@flash110

Usually, when a singleton doesn't need extra data during initialization, it takes this form:

Code:

private static ClassName instance;

public static ClassName getInstance() {
    if (instance == null) {
        instance = new ClassName();
    }
    return instance;
}

This way it is implicitly initialized the first time it is needed.

 

@mythbusterma Okay, at least I didn't have it completely wrong I'll go try that now and edit this comment with what happened. EDIT:
After fixing up the code with what you suggested the sane error occured, and it happens when calling

Code:

 teams.initializeTeam("blue", ChatColor.BLUE.toString()); 

from the Teams class. I think it has to do with the main scoreboard it gets from the main class right before that. I made a test method in the Teams class with a simple bit that just prints something to console and it worked. It just cant call the initializeTeam method... If anyone else has any ideas why, let me know. @mine-care since you have solved one of my problems before, do you have any ideas?

 

@flash110

I can't see your code, I can't help you.

 

Oops I forgot to update this thread. I got it to work so I'm setting it to solved now.