观察到
- 处理程序是私有的和最终的
- handler.clazz是最终的
RuleHandler<T extends Rule>
暗示RuleHandler<?> === RuleHandler<? extends Rule>
以下代码正确（并编译）
abstract class RuleHandler<T extends Rule>{ final Class<T> clazz; // as before}class HandlerDispatcher{ private final Map<Class<?>, RuleHandler<?>> handlers; void register(RuleHandler<?> handler) { handlers.put(handler.clazz, handler); } void doStuff(List<Rule> rules) { for(Rule rule : rules) { @SuppressWarnings("unchecked") RuleHandler<Rule> handler = (RuleHandler<Rule>) handlers.get(rule.getClass()); handler.doStuff(rule); } }}class Test{ void main() { HandlerDispatcher hd = new HandlerDispatcher(); hd.register(new ExampleRuleHandler()); RuleHandler<?> handler = new ExampleRuleHandler(); hd.register(handler); }}
