这将为你提供Multitons的线程安全存储机制。唯一的缺点是可以创建在putIfAbsent()调用中不使用的Multiton。可能性很小,但确实存在。当然,尽管确实有发生,但仍不会造成任何伤害。
从好的方面来说,不需要预分配或初始化,也没有预定义的大小限制。
private static ConcurrentHashMap<Integer, Multiton> instances = new ConcurrentHashMap<Integer, Multiton>();
public static Multiton getInstance(int which)
{
Multiton result = instances.get(which);
if (result == null)
{
Multiton m = new Multiton(...);
result = instances.putIfAbsent(which, m);
if (result == null)
result = m;
}
return result;
}
使用Java 8,它甚至可以更简单:
public class Multiton {
private static final ConcurrentMap<String, Multiton> multitons = new ConcurrentHashMap<>();
private final String key;
private Multiton(String key) { this.key = key; }
public static Multiton getInstance(final String key) {
return multitons.computeIfAbsent(key, Multiton::new);
}
}