Kill roughly 80% of your boilerplate code

AbstractCriterionTrigger.java

/*
 * This is free and unencumbered software released into the public domain.
 *
 * Anyone is free to copy, modify, publish, use, compile, sell, or
 * distribute this software, either in source code form or as a compiled
 * binary, for any purpose, commercial or non-commercial, and by any
 * means.
 *
 * In jurisdictions that recognize copyright laws, the author or authors
 * of this software dedicate any and all copyright interest in the
 * software to the public domain. We make this dedication for the benefit
 * of the public at large and to the detriment of our heirs and
 * successors. We intend this dedication to be an overt act of
 * relinquishment in perpetuity of all present and future rights to this
 * software under copyright law.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
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package frogcraftrebirth.common.advancement;

import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonObject;
import net.minecraft.advancements.ICriterionTrigger;
import net.minecraft.advancements.PlayerAdvancements;
import net.minecraft.advancements.critereon.AbstractCriterionInstance;
import net.minecraft.entity.player.EntityPlayerMP;
import net.minecraft.util.ResourceLocation;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.IdentityHashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;

public abstract class AbstractCriterionTrigger<C, I extends AbstractCriterionTrigger.Instance<C>> implements ICriterionTrigger<I> {

	private final ResourceLocation identifier;
	
	// TODO (3TUSK): HashMap or IdentityHashMap?
	private final Map<PlayerAdvancements, Set<Listener<I>>> trackers = new IdentityHashMap<>();

	protected AbstractCriterionTrigger(ResourceLocation identifier) {
		this.identifier = identifier;
	}

	@Override
	public final ResourceLocation getId() {
		return this.identifier;
	}

	@Override
	public final void addListener(PlayerAdvancements playerAdvancements, Listener<I> listener) {
		this.trackers.computeIfAbsent(playerAdvancements, unused -> new HashSet<>()).add(listener);
	}

	@Override
	public final void removeListener(PlayerAdvancements playerAdvancements, Listener<I> listener) {
		Set<Listener<I>> tracker = this.trackers.get(playerAdvancements);
		if (tracker != null) {
			tracker.remove(listener);
			if (tracker.isEmpty()) {
				this.trackers.remove(playerAdvancements);
			}
		}
	}

	@Override
	public final void removeAllListeners(PlayerAdvancements playerAdvancements) {
		this.trackers.remove(playerAdvancements);
	}

	@Override
	public abstract I deserializeInstance(JsonObject json, JsonDeserializationContext context);

	public final void trigger(EntityPlayerMP player, C context) {
		PlayerAdvancements advancements = player.getAdvancements();
		Set<Listener<I>> listeners = this.trackers.get(advancements);
		if (listeners != null) {
			List<Listener<I>> triggered = new ArrayList<>();
			for (Listener<I> listener : listeners) {
				if (listener.getCriterionInstance().test(context)) {
					triggered.add(listener);
				}
			}
			for (Listener<I> listener : triggered) {
				listener.grantCriterion(advancements);
			}
		}
	}

	protected static abstract class Instance<C> extends AbstractCriterionInstance {

		protected Instance(ResourceLocation identifier) {
			super(identifier);
		}

		public abstract boolean test(C context);
	}
}