如何使此嵌套通用参数系统正常工作？

Question

因此，我正在尝试使一个相当复杂的系统正常工作。这是我正在尝试的基础知识。

规则：

abstract class Rule
{
  // stuff
}

class ExampleRule extends Rule
{
  // stuff
}

处理程序：

abstract class RuleHandler<T extends Rule>
{
  Class<T> clazz;
  RuleHandler(Class<T> forClass)
  {
    this.clazz = forClass;
  }
  abstract void doStuff(T rule);
}

class ExampleRuleHandler extends RuleHandler<ExampleRule>
{
  ExampleRuleHandler()
  {
    super(ExampleRule.class);
  }
  void doStuff(ExampleRule rule)
  {
    // stuff
  }
}

并将它们绑在一起：

class HandlerDispatcher
{
  Map<Class<? extends Rule>, RuleHandler<? extends Rule>> handlers;
  void register(RuleHandler<? extends Rule> handler)
  {
    handlers.put(handler.clazz, handler);
  }
  void doStuff(List<Rule> rules)
  {
    for(Rule rule : rules)
    {
      RuleHandler<? extends Rule> handler = handlers.get(rule.getClass());
      handler.doStuff(rule);
    }
  }
}

class Test
{
  void main()
  {
    HandlerDispatcher hd = new HandlerDispatcher();
    hd.register(new ExampleRuleHandler());
  }
}

到目前为止，我已经尝试了不同参数（通配符，受限符等）的各种组合，并且还没有进行与类型相关的错误的编译。欢迎任何见解，解决方案或替代方法。

Answer 1

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);
  }
}