Thread: Accurate NPC Drop Chance System

nice prob going to use do you mind showing the file build up ?

Originally Posted by Michael P

Not a lot of people seem to have very accurate NPC drop chance systems, so here you go. Enjoy.

I do NOT give permission to re-release and/or distribute this in anyway.

Code:

package org.rs_reborn.game.model.npcs.drop;

import java.util.Random;

/**
 * Represents an npc drop chance.
 * 
 * @author Michael P
 *
 */
public enum NpcDropChance {

	ALWAYS(1),
	COMMON("2-50"),
	UNCOMMON("51-100"),
	RARE("101-512"),
	VERY_RARE("513-1000");
	
	/**
	 * The rate of the chance.
	 */
	private final Object rate;
	
	/**
	 * The {@link Random} used for generating a random number.
	 */
	private final Random random = new Random();
	
	/**
	 * Constructs new a {@link NpcDropChance}.
	 * 
	 * @param rate
	 *            The rate {@link Object}.
	 */
	private NpcDropChance(Object rate) {
		this.rate = rate;
	}
	
	/**
	 * Checks to see if the chance is a success.
	 * @return If the chance is a success {@code true};
	 * if not {@code false}.
	 */
	public boolean isSuccess() {
		if (rate instanceof String) {
			String[] args = ((String) rate).split("-");
			int n = getN(Integer.parseInt(args[0]), Integer.parseInt(args[1]));
			int success = Integer.parseInt(args[0]);
			return n % success == 0;
		}
		return true; // rate is 1 (ALWAYS), therefore it's a success 100%.
	}
	
	/**
	 * Gets a random number within a certain range.
	 * 
	 * @param min
	 *            The minimum number range.
	 * @param max
	 *            The maximum number range.
	 * @return The random number.
	 */
	private int getN(int min, int max) {
		final int n = Math.abs(max - min);
		return Math.min(min, max) + (n == 0 ? 0 : random.nextInt(n));
	}
	
}

Here is a dump of the drop attempts using this system for those who want to see the accuracy of it.

Code:

Took 0 attempts for: COMMON
Took 0 attempts for: COMMON
Took 2 attempts for: COMMON
Took 0 attempts for: COMMON
Took 2 attempts for: COMMON
<----    New Drop    ---->
 
Took 162 attempts for: UNCOMMON
Took 8 attempts for: UNCOMMON
Took 112 attempts for: UNCOMMON
Took 2 attempts for: UNCOMMON
Took 39 attempts for: UNCOMMON
<----    New Drop    ---->
 
Took 15 attempts for: RARE
Took 47 attempts for: RARE
Took 123 attempts for: RARE
Took 180 attempts for: RARE
Took 70 attempts for: RARE
<----    New Drop    ---->
 
Took 335 attempts for: VERY_RARE
Took 518 attempts for: VERY_RARE
Took 1215 attempts for: VERY_RARE
Took 88 attempts for: VERY_RARE
Took 123 attempts for: VERY_RARE
<----    New Drop    ---->

Why have an Object field if you're only parsing a String object?

Code:

/**
	 * Constructs new a {@link NpcDropChance}.
	 * 
	 * @param rate
	 *            The rate {@link Object}.
	 */
	private NpcDropChance(String rate) {
		this.rate = rate;
	}

Is what it should look like.

If you want to use a String design for the rate at least parse it on initiation to local variables: int minRange, int maxRange

Code:

public final int minRange, maxRange;

NpcDropChance(Object rate) {
    if(rate instanceof String) {
        String[] s = ((String) rate).split("-");
        minRange = Integer.valueOf(s[0]);
        maxRange = Integer.valueOf(s[1]);
        return;
    }
    minRange = maxRange = (Integer) rate;
}

In a heavy populated server my guess is that 'isSucess' will be called very often.
This will cause for a lot of unneeded overhead each call by checking if the value is in fact a String object, splitting the value, and finally parsing the split results.