java random by weight

使用反射實現了一個通用的random by weight，只要被隨機的結構中帶有getWeight函數即可

public static <T extends Object>
T getRandomObjByWeight(List<T> objs, Class<?> clazz) {
	try {
		Method getWeightFunc = clazz.getMethod("getWeight");

		Double totalWeight = 0.0;
		for(Object obj : objs) {
			Integer weight = (Integer)getWeightFunc.invoke(obj);
			totalWeight += Double.valueOf(weight);
		}

		double random = Math.random() * totalWeight;
		for(T obj : objs) {
			Integer weight = (Integer)getWeightFunc.invoke(obj);
			random -= Double.valueOf(weight);
			if (random <= 0.0) {
				return obj;
			}
		}
	} catch (Exception e) {
		LogUtil.LOG_BASE.error("getRandomObjByWeight異常",  e.getMessage(),  e);
	}

	return null;
}

測試代碼

public class Item {
	private Integer id;
	private Integer weight;

	public Item(Integer id, Integer weight) {
		this.id = id;
		this.weight = weight;
	}

	public Integer getId() {
		return id;
	}

	public void setId(Integer id) {
		this.id = id;
	}

	public Integer getWeight() {
		return weight;
	}

	public void setWeight(Integer weight) {
		this.weight = weight;
	}
}

public static void main(String[] args) {
	List<Item> items = new ArrayList<>();

	items.add(new Item(1, 50));
	items.add(new Item(2, 50));
	items.add(new Item(3, 50));

	Map<Integer, Integer> counts = new HashMap<>();

	for (int i = 0; i < 1000; ++i) {
		Item item = GameUtil.getRandomObjByWeight(items, Item.class);

		Integer count = counts.get(item.id);
		if (count == null) {
			counts.put(item.id, 1);
		} else {
			counts.put(item.id, count+1);
		}
	}

	Integer total = 0;
	for (Map.Entry<Integer, Integer> pair : counts.entrySet()) {
		System.out.println("id=" + pair.getKey() + " count=" + pair.getValue());

		total += pair.getValue();
	}

	System.out.println("total=" + total);
}