Java中的线程安全多态

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);    }}