了解 Java 方法声明中的<Req 扩展请求<Res>，Res 扩展响应>

Question

我一直在尝试破译Alexa for Java的智能家居指令API，遇到了一个我以前从未见过的结构，无法弄清楚如何在搜索中引用它是什么。 我知道泛型，但这显然是不同的(至少我认为(。 谁能向我解释使用<Req extends Request <Res>, Res extends Response>的受保护方法声明中发生了什么？

public abstract class SmartHomeDirectiveHandler implements 
RequestStreamHandler {
private static Gson gson = new Gson();
private static HandlerFactory factory = new HandlerFactory();
protected <Req extends Request<Res>, Res extends Response> void 
registerHandler(MessageName name,RequestHandler<Req, Res> handler) {
factory.registerHandler(name, handler);
}
abstract protected void init();
protected SmartHomeDirectiveHandler() {
this.init();
}
public final void handleRequest(InputStream inputStream, OutputStream 
outputStream, Context context) throws IOException {
JsonReader reader = new JsonReader(new 
InputStreamReader(inputStream));
SmartHomeDirectiveRequest request = gson.fromJson(reader, 
SmartHomeDirectiveRequest.class);
RequestHandler handler = 
factory.getHandler(request.getHeader().getName());
Request req = PayloadDeserializer.deserializePayload(request);
Response responsePayload;
try {
responsePayload = handler.handle(req);
} catch (Exception e) {
throw new IOException(e);
}

SmartHomeDirectiveResponse response = new 
SmartHomeDirectiveResponse();
Header responseHeader = new Header();
responseHeader.setName(responsePayload.getMessageName());
responseHeader.setMessageId(request.getHeader().getMessageId());
responseHeader.setPayloadVersion(request.getHeader()
.getPayloadVersion());
responseHeader.setNamespace(request.getHeader().getNamespace());
response.setHeader(responseHeader);
response.setPayload(responsePayload);
OutputStreamWriter writer = new OutputStreamWriter(outputStream);
writer.write(gson.toJson(response, 
SmartHomeDirectiveResponse.class));
writer.flush();
}
}

Answer 1

为了简化答案，一个带有泛型参数的方法定义如下：

public <T> void methodName(T parameterName){
//stuff 
}

在您的情况下，该方法有两种泛型类型，因此(再次简化(它是：

public <T,E> void methodName(T parameterName, E parameterTwoName){
//stuff 
}

最后，这些泛型有一个上限，所以结果：

public <T  extends Request<E>  ,E extends Response > void methodName(T parameterName, E parameterTwoName){
//stuff 
}