weighted-random-selection

weighted-random-selection

package com.mkayman;

import java.util.Arrays;
import java.util.List;

public class Main {

  public static void main(String[] args) {
		List<Item> items = Arrays.asList(new Item("item1", 40), new Item(
				"item2", 10), new Item("item3", 10), new Item("item4", 10),
				new Item("item5", 30));

		double totalWeight = 0.0d;

		for (Item item : items) {
			totalWeight += item.weight;
		}

		for (int i = 1; i <= 10000; i++) {
			double random = Math.random() * totalWeight;
			
			for (Item item : items) {
				random -= item.weight;
				
				if (random <= 0.0d) {
					sum(item.name);
					break;
				}
			}
		}
		
		System.out.println("item1: " + item1);
		System.out.println("item2: " + item2);
		System.out.println("item3: " + item3);
		System.out.println("item4: " + item4);
		System.out.println("item5: " + item5);
	}
	
	static int item1, item2, item3, item4, item5;
	
	static void sum(String name) {
		if (name == "item1") item1++;
		else if (name == "item2") item2++;
		else if (name == "item3") item3++;
		else if (name == "item4") item4++;
		else if (name == "item5") item5++;
	}

	static class Item {
		public String name;
		public double weight;

		public Item(String name, double weight) {
			this.name = name;
			this.weight = weight;
		}
	}
}