public class StrategyPattern {

    public static void main(String[] args) {

        Context context = new Context();
//        context.setStrategy(new AndStrategy());
        context.setStrategy(new OrStrategy());
        context.deploy(2,1);

    }

//环境类，算法执行的上下文环境
    static class Context {
        private Strategy strategy;

        public Context(Strategy strategy) {
            this.strategy = strategy;
        }

        public Context() {
        }

        public void setStrategy(Strategy strategy) {
            this.strategy = strategy;
        }

        public void deploy(int a, int b) {
            if (strategy != null) {
                int result = strategy.deploy(a, b);
                System.out.println("result:" + result);
            }
        }
    }

//抽象策略类
    interface Strategy {
        int deploy(int a, int b);
    }

//具体策略类
    static class AndStrategy implements Strategy {

        public int deploy(int a, int b) {
            return a & b;
        }
    }
//具体策略类
    static class OrStrategy implements Strategy {

        public int deploy(int a, int b) {
            return a | b;
        }
    }

}

//通过forName方法获得(带有包名的真实类路径)
 Class<?> mClass = Class.forName("java.util.ArrayList");

//直接通过类.class
Class<?> mClass = ArrayList.class;

//通过对象.getClass()
Class<?> mClass = list.getClass();

//得到所有构造函数
  Constructor<?>[] constructors = mClass.getConstructors();
            for (Constructor<?> constructor : constructors) {
                System.out.println(constructor);
            }

//获得特定构造函数
Constructor<ArrayList> constructor = mClass.getConstructor(null);

//得到共有的public方法 包括继承的方法
Method[] methods=  mClass.getMethods();

//得到类所有方法 包括public private protect
Method[] methods = mClass.getDeclaredMethods();

//得到特定对象，并执行实例该方法
 Method method = mClass.getMethod("add", Object.class);
                if (method != null) {
                    try {
                        method.invoke(list, 1245);
                    } catch (IllegalAccessException e) {
                        e.printStackTrace();
                    } catch (InvocationTargetException e) {
                        e.printStackTrace();
                    }
                }

//获取所有共有的public变量，包括继承的属性
 Field[] fields = mClass.getFields();
            for (Field field : fields) {
                System.out.println(field);
            }

//获取所有申明的变量 public private protect
 Field[] fields = mClass.getDeclaredFields();
            for (Field field : fields) {
                System.out.println(field);
            }

//设置变量值
field.set(list,12l);

//通过反射得到的构造函数创建ArrayList实例，添加了两个元素ok和12
 Constructor<?>[] constructors = mClass.getConstructors();
            for (Constructor<?> constructor : constructors) {
                System.out.println(constructor);
            }

            try {
                ArrayList l = (ArrayList) constructors[1].newInstance();
                l.add("ok");
                l.add(12);
                System.out.println(l.size());
            } catch (InstantiationException | IllegalAccessException | InvocationTargetException e) {
                e.printStackTrace();
            }

public class ClassA<T> {

        public void print(T t) {
            System.out.println("class is" + t.getClass());
        }
    }

interface IA<T> {

       T getThing();
   }

public <T> void print(T t) {
            System.out.println("class is" + t.getClass());
        }

ArrayList<Integer> listA = new ArrayList<>();
listA.add(12);
System.out.println("listA type is" + (listA.get(0).getClass()));

ArrayList<String> list = new ArrayList<>();
list.add(12);//报错 编译不能通过
String s = list.get(0);//返回的是String类型

ArrayList list1 = new ArrayList<String>();
list1.add(12);//编译通过
Object ob1 = list1.get(0);//返回的是Object

ArrayList<String> list = new ArrayList<>();
t1(list);//编译不通过，类型检测ArrayList<String>与ArrayList<Object>数组结构不一样
 private void t1(ArrayList<Object> l) {
 }

//创建接口IFanSheDuoTai，申明方法，方法参数类型是泛型T；
public interface IFanSheDuoTai<T> {

    public void test(T t);

}

//实现类FanSheDuoTai 重写方法test
public class FanSheDuoTai implements IFanSheDuoTai<String> {

    public static void main(String[] args) {

    }

    @Override
    public void test(String s) {

    }
}

public class com.litchi.demo.FanSheDuoTai implements com.litchi.demo.IFanSheDuoTai<java.lang.String> {
  public com.litchi.demo.FanSheDuoTai();
  public static void main(java.lang.String[]);
  public void test(java.lang.String);
  public void test(java.lang.Object);
}

Type componentType = ((GenericArrayType)type).getGenericComponentType();

class A{

        IB b;

        public A(IB b) {
        }
        
        public void doA(){
            if (b != null) {
                b.doThing();
            }
        }
    }
    
    class B implements IB{

        @Override
        public void doThing() {
            System.out.println("B do some thing");
        }
    }
    
    interface IB{
        void doThing();
    }

public synchronized ExecutorService executorService() {
    if (executorService == null) {
      executorService = new ThreadPoolExecutor(0, Integer.MAX_VALUE, 60, TimeUnit.SECONDS,
          new SynchronousQueue<Runnable>(), Util.threadFactory("OkHttp Dispatcher", false));
    }
    return executorService;
  }

//(1) builder模式配置参数构建request对象
 Request request = new Request.Builder()
                .url("http://baidu.com?key=values")
                .get()
                .build();
            //(2)builder构建OkHttpClient对象
        new OkHttpClient.Builder().build()
                .newCall(request)//(3)request入参返回RealCall
                .enqueue(new okhttp3.Callback() {//(4)请求回调
                    @Override
                    public void onFailure(Call call, IOException e) {
                        System.out.println(e.getMessage());
                    }

                    @Override
                    public void onResponse(Call call, Response response) throws IOException {
                        System.out.println("thread:"+Thread.currentThread());
                        if (response.isSuccessful()) {
                            ResponseBody responseBody = response.body();
                            data.setText(responseBody.string());
                        }

                    }
                });

/**
 * An HTTP request. Instances of this class are immutable if their {@link #body} is null or itself
 * immutable.
 */
public final class Request {
  final HttpUrl url;
  final String method;
  final Headers headers;
  final @Nullable RequestBody body;
  final Object tag;

  private volatile CacheControl cacheControl; // Lazily initialized.

  Request(Builder builder) {
    this.url = builder.url;
    this.method = builder.method;
    this.headers = builder.headers.build();
    this.body = builder.body;
    this.tag = builder.tag != null ? builder.tag : this;
  }
    /**
     * Attaches {@code tag} to the request. It can be used later to cancel the request. If the tag
     * is unspecified or null, the request is canceled by using the request itself as the tag.
     */
    public Builder tag(Object tag) {
      this.tag = tag;
      return this;
    }

    public Request build() {
      if (url == null) throw new IllegalStateException("url == null");
      return new Request(this);
    }
  }
}

OkHttpClient(Builder builder) {
    this.dispatcher = builder.dispatcher;//（1）分发器
    this.proxy = builder.proxy;//（2）代理类
    this.protocols = builder.protocols;//（3）协议类
    this.connectionSpecs = builder.connectionSpecs;//（4）连接规模 确定TLS版本和密码套件
    this.interceptors = Util.immutableList(builder.interceptors);//（5）自定义应用拦截器
    this.networkInterceptors = Util.immutableList(builder.networkInterceptors);//（6）自定义网络拦截器
    this.eventListenerFactory = builder.eventListenerFactory;//（7）事件监听工厂
    this.proxySelector = builder.proxySelector;//（8）代理选择器
    this.cookieJar = builder.cookieJar;
    this.cache = builder.cache;//（9）缓冲类
    this.internalCache = builder.internalCache;//（10）
    this.socketFactory = builder.socketFactory;//（11）socket工厂
    
     boolean isTLS = false;
    for (ConnectionSpec spec : connectionSpecs) {
      isTLS = isTLS || spec.isTls();
    }

    if (builder.sslSocketFactory != null || !isTLS) {
      this.sslSocketFactory = builder.sslSocketFactory;
      this.certificateChainCleaner = builder.certificateChainCleaner;
    } else {
      X509TrustManager trustManager = systemDefaultTrustManager();
      this.sslSocketFactory = systemDefaultSslSocketFactory(trustManager);
      this.certificateChainCleaner = CertificateChainCleaner.get(trustManager);
    }

    this.hostnameVerifier = builder.hostnameVerifier;
    this.certificatePinner = builder.certificatePinner.withCertificateChainCleaner(
        certificateChainCleaner);
    this.proxyAuthenticator = builder.proxyAuthenticator;
    this.authenticator = builder.authenticator;
    this.connectionPool = builder.connectionPool;//（12）连接池
    this.dns = builder.dns;
    this.followSslRedirects = builder.followSslRedirects;
    this.followRedirects = builder.followRedirects;
    this.retryOnConnectionFailure = builder.retryOnConnectionFailure;
    this.connectTimeout = builder.connectTimeout;
    this.readTimeout = builder.readTimeout;
    this.writeTimeout = builder.writeTimeout;
  }

/**
  * Prepares the {@code request} to be executed at some point in the future.
  */
 @Override public Call newCall(Request request) {
   return RealCall.newRealCall(this, request, false /* for web socket */);
 }

static RealCall newRealCall(OkHttpClient client, Request originalRequest, boolean forWebSocket) {
    // Safely publish the Call instance to the EventListener.
    RealCall call = new RealCall(client, originalRequest, forWebSocket);//(1)
    call.eventListener = client.eventListenerFactory().create(call);//(2)
    return call;
  }

@Override public void enqueue(Callback responseCallback) {
   synchronized (this) {
     if (executed) throw new IllegalStateException("Already Executed");（1）
     executed = true;
   }
   captureCallStackTrace();（2）
   eventListener.callStart(this);（3）
   client.dispatcher().enqueue(new AsyncCall(responseCallback));//（4）
 }

synchronized void enqueue(AsyncCall call) {
   if (runningAsyncCalls.size() < maxRequests && runningCallsForHost(call) < maxRequestsPerHost) {//（1）
     runningAsyncCalls.add(call);//（2）
     executorService().execute(call);//（3）
   } else {
     readyAsyncCalls.add(call);//（4）
   }
 }

@Override protected void execute() {
     boolean signalledCallback = false;
     try {
       Response response = getResponseWithInterceptorChain();//（1）
       if (retryAndFollowUpInterceptor.isCanceled()) {//（2）
         signalledCallback = true;
         responseCallback.onFailure(RealCall.this, new IOException("Canceled"));
       } else {
         signalledCallback = true;
         responseCallback.onResponse(RealCall.this, response);//（3）
       }
     } catch (IOException e) {
       if (signalledCallback) {
         // Do not signal the callback twice!
         Platform.get().log(INFO, "Callback failure for " + toLoggableString(), e);
       } else {
         eventListener.callFailed(RealCall.this, e);//（4）
         responseCallback.onFailure(RealCall.this, e);//（5）
       }
     } finally {
       client.dispatcher().finished(this);//（6）
     }
   }

Response getResponseWithInterceptorChain() throws IOException {
    // Build a full stack of interceptors.
    List<Interceptor> interceptors = new ArrayList<>();
    interceptors.addAll(client.interceptors());//(1)
    interceptors.add(retryAndFollowUpInterceptor);//(2)
    interceptors.add(new BridgeInterceptor(client.cookieJar()));//(3)
    interceptors.add(new CacheInterceptor(client.internalCache()));//(4)
    interceptors.add(new ConnectInterceptor(client));//(5)
    if (!forWebSocket) {
      interceptors.addAll(client.networkInterceptors());//(6)
    }
    interceptors.add(new CallServerInterceptor(forWebSocket));//(7)

    Interceptor.Chain chain = new RealInterceptorChain(interceptors, null, null, null, 0,
        originalRequest, this, eventListener, client.connectTimeoutMillis(),
        client.readTimeoutMillis(), client.writeTimeoutMillis());

    return chain.proceed(originalRequest);//(8)
  }

public Response proceed(Request request, StreamAllocation streamAllocation, HttpCodec httpCodec,
      RealConnection connection) throws IOException {
    if (index >= interceptors.size()) throw new AssertionError();

    calls++;

    // If we already have a stream, confirm that the incoming request will use it.
    if (this.httpCodec != null && !this.connection.supportsUrl(request.url())) {
      throw new IllegalStateException("network interceptor " + interceptors.get(index - 1)
          + " must retain the same host and port");
    }

    // If we already have a stream, confirm that this is the only call to chain.proceed().
    if (this.httpCodec != null && calls > 1) {
      throw new IllegalStateException("network interceptor " + interceptors.get(index - 1)
          + " must call proceed() exactly once");
    }

    // Call the next interceptor in the chain.
    RealInterceptorChain next = new RealInterceptorChain(interceptors, streamAllocation, httpCodec,
        connection, index + 1, request, call, eventListener, connectTimeout, readTimeout,
        writeTimeout);
    Interceptor interceptor = interceptors.get(index);
    Response response = interceptor.intercept(next);//(1)

    // Confirm that the next interceptor made its required call to chain.proceed().
    if (httpCodec != null && index + 1 < interceptors.size() && next.calls != 1) {
      throw new IllegalStateException("network interceptor " + interceptor
          + " must call proceed() exactly once");
    }

    // Confirm that the intercepted response isn't null.
    if (response == null) {
      throw new NullPointerException("interceptor " + interceptor + " returned null");
    }

    if (response.body() == null) {
      throw new IllegalStateException(
          "interceptor " + interceptor + " returned a response with no body");
    }

    return response;
  }

@Override public Response intercept(Chain chain) throws IOException {
  Request request = chain.request();
  RealInterceptorChain realChain = (RealInterceptorChain) chain;
  Call call = realChain.call();
  EventListener eventListener = realChain.eventListener();

  StreamAllocation streamAllocation = new StreamAllocation(client.connectionPool(),
      createAddress(request.url()), call, eventListener, callStackTrace);//（1）
  this.streamAllocation = streamAllocation;

  int followUpCount = 0;
  Response priorResponse = null;
  while (true) {
    if (canceled) {
      streamAllocation.release();//（2）
      throw new IOException("Canceled");
    }

    Response response;
    boolean releaseConnection = true;
    try {
      response = realChain.proceed(request, streamAllocation, null, null);//（3）
      releaseConnection = false;
    } catch (RouteException e) {
      // The attempt to connect via a route failed. The request will not have been sent.
      if (!recover(e.getLastConnectException(), streamAllocation, false, request)) {
        throw e.getLastConnectException();//（4）
      }
      releaseConnection = false;
      continue;
    } catch (IOException e) {
      // An attempt to communicate with a server failed. The request may have been sent.
      boolean requestSendStarted = !(e instanceof ConnectionShutdownException);
      if (!recover(e, streamAllocation, requestSendStarted, request)) throw e;
      releaseConnection = false;//（5）
      continue;
    } finally {
      // We're throwing an unchecked exception. Release any resources.
      if (releaseConnection) {//（6）
        streamAllocation.streamFailed(null);
        streamAllocation.release();
      }
    }

    // Attach the prior response if it exists. Such responses never have a body.
    if (priorResponse != null) {//（7）
      response = response.newBuilder()
          .priorResponse(priorResponse.newBuilder()
                  .body(null)
                  .build())
          .build();
    }

    Request followUp = followUpRequest(response, streamAllocation.route());//（8）

    if (followUp == null) {//（9）
      if (!forWebSocket) {
        streamAllocation.release();
      }
      return response;
    }

    closeQuietly(response.body());//（10）

    if (++followUpCount > MAX_FOLLOW_UPS) {//（11）
      streamAllocation.release();
      throw new ProtocolException("Too many follow-up requests: " + followUpCount);
    }

    if (followUp.body() instanceof UnrepeatableRequestBody) {//（12）
      streamAllocation.release();
      throw new HttpRetryException("Cannot retry streamed HTTP body", response.code());
    }

    if (!sameConnection(response, followUp.url())) {//（13）
      streamAllocation.release();
      streamAllocation = new StreamAllocation(client.connectionPool(),
          createAddress(followUp.url()), call, eventListener, callStackTrace);
      this.streamAllocation = streamAllocation;
    } else if (streamAllocation.codec() != null) {//（14）
      throw new IllegalStateException("Closing the body of " + response
          + " didn't close its backing stream. Bad interceptor?");
    }

    request = followUp;//（15）
    priorResponse = response;//（16）
  }
}

@Override public Response intercept(Chain chain) throws IOException {
   Request userRequest = chain.request();
   Request.Builder requestBuilder = userRequest.newBuilder();

   RequestBody body = userRequest.body();
   if (body != null) {
     MediaType contentType = body.contentType();
     if (contentType != null) {
       requestBuilder.header("Content-Type", contentType.toString());//（1）
     }

     long contentLength = body.contentLength();
     if (contentLength != -1) {
       requestBuilder.header("Content-Length", Long.toString(contentLength));
       requestBuilder.removeHeader("Transfer-Encoding");
     } else {
       requestBuilder.header("Transfer-Encoding", "chunked");
       requestBuilder.removeHeader("Content-Length");
     }
   }

   if (userRequest.header("Host") == null) {
     requestBuilder.header("Host", hostHeader(userRequest.url(), false));
   }

   if (userRequest.header("Connection") == null) {
     requestBuilder.header("Connection", "Keep-Alive");
   }

   // If we add an "Accept-Encoding: gzip" header field we're responsible for also decompressing
   // the transfer stream.
   boolean transparentGzip = false;
   if (userRequest.header("Accept-Encoding") == null && userRequest.header("Range") == null) {
     transparentGzip = true;
     requestBuilder.header("Accept-Encoding", "gzip");
   }

   List<Cookie> cookies = cookieJar.loadForRequest(userRequest.url());
   if (!cookies.isEmpty()) {
     requestBuilder.header("Cookie", cookieHeader(cookies));
   }

   if (userRequest.header("User-Agent") == null) {
     requestBuilder.header("User-Agent", Version.userAgent());
   }

   Response networkResponse = chain.proceed(requestBuilder.build());

   HttpHeaders.receiveHeaders(cookieJar, userRequest.url(), networkResponse.headers());

   Response.Builder responseBuilder = networkResponse.newBuilder()
       .request(userRequest);

   if (transparentGzip
       && "gzip".equalsIgnoreCase(networkResponse.header("Content-Encoding"))
       && HttpHeaders.hasBody(networkResponse)) {
     GzipSource responseBody = new GzipSource(networkResponse.body().source());
     Headers strippedHeaders = networkResponse.headers().newBuilder()
         .removeAll("Content-Encoding")
         .removeAll("Content-Length")
         .build();
     responseBuilder.headers(strippedHeaders);
     String contentType = networkResponse.header("Content-Type");
     responseBuilder.body(new RealResponseBody(contentType, -1L, Okio.buffer(responseBody)));
   }

   return responseBuilder.build();
 }

@Override public Response intercept(Chain chain) throws IOException {
    Response cacheCandidate = cache != null
        ? cache.get(chain.request())
        : null;

    long now = System.currentTimeMillis();

//（1）
    CacheStrategy strategy = new CacheStrategy.Factory(now, chain.request(), cacheCandidate).get();
    Request networkRequest = strategy.networkRequest;
    Response cacheResponse = strategy.cacheResponse;

    if (cache != null) {
      cache.trackResponse(strategy);
    }

    if (cacheCandidate != null && cacheResponse == null) {//（2）
      closeQuietly(cacheCandidate.body()); // The cache candidate wasn't applicable. Close it.
    }

    // If we're forbidden from using the network and the cache is insufficient, fail.
    if (networkRequest == null && cacheResponse == null) {//（3）
      return new Response.Builder()
          .request(chain.request())
          .protocol(Protocol.HTTP_1_1)
          .code(504)
          .message("Unsatisfiable Request (only-if-cached)")
          .body(Util.EMPTY_RESPONSE)
          .sentRequestAtMillis(-1L)
          .receivedResponseAtMillis(System.currentTimeMillis())
          .build();
    }

    // If we don't need the network, we're done.
    if (networkRequest == null) {//（4）
      return cacheResponse.newBuilder()
          .cacheResponse(stripBody(cacheResponse))
          .build();
    }

    Response networkResponse = null;
    try {
      networkResponse = chain.proceed(networkRequest);
    } finally {
      // If we're crashing on I/O or otherwise, don't leak the cache body.
      if (networkResponse == null && cacheCandidate != null) {
        closeQuietly(cacheCandidate.body());//（5）
      }
    }

    // If we have a cache response too, then we're doing a conditional get.
    if (cacheResponse != null) {//（6）
      if (networkResponse.code() == HTTP_NOT_MODIFIED) {
        Response response = cacheResponse.newBuilder()
            .headers(combine(cacheResponse.headers(), networkResponse.headers()))
            .sentRequestAtMillis(networkResponse.sentRequestAtMillis())
            .receivedResponseAtMillis(networkResponse.receivedResponseAtMillis())
            .cacheResponse(stripBody(cacheResponse))
            .networkResponse(stripBody(networkResponse))
            .build();
        networkResponse.body().close();

        // Update the cache after combining headers but before stripping the
        // Content-Encoding header (as performed by initContentStream()).
        cache.trackConditionalCacheHit();
        cache.update(cacheResponse, response);
        return response;
      } else {
        closeQuietly(cacheResponse.body());
      }
    }

//（7）
    Response response = networkResponse.newBuilder()
        .cacheResponse(stripBody(cacheResponse))
        .networkResponse(stripBody(networkResponse))
        .build();

    if (cache != null) {
      if (HttpHeaders.hasBody(response) && CacheStrategy.isCacheable(response, networkRequest)) {
        // Offer this request to the cache.
        CacheRequest cacheRequest = cache.put(response);//（8）
        return cacheWritingResponse(cacheRequest, response);
      }

      if (HttpMethod.invalidatesCache(networkRequest.method())) {
        try {
          cache.remove(networkRequest);
        } catch (IOException ignored) {
          // The cache cannot be written.
        }
      }
    }

    return response;
  }

@Override public Response intercept(Chain chain) throws IOException {
    RealInterceptorChain realChain = (RealInterceptorChain) chain;
    Request request = realChain.request();
    StreamAllocation streamAllocation = realChain.streamAllocation();

    // We need the network to satisfy this request. Possibly for validating a conditional GET.
    boolean doExtensiveHealthChecks = !request.method().equals("GET");
    HttpCodec httpCodec = streamAllocation.newStream(client, chain, doExtensiveHealthChecks);
    RealConnection connection = streamAllocation.connection();//（1）

    return realChain.proceed(request, streamAllocation, httpCodec, connection);
  }

 @Override public Response intercept(Chain chain) throws IOException {
    RealInterceptorChain realChain = (RealInterceptorChain) chain;
    HttpCodec httpCodec = realChain.httpStream();
    StreamAllocation streamAllocation = realChain.streamAllocation();
    RealConnection connection = (RealConnection) realChain.connection();
    Request request = realChain.request();

    long sentRequestMillis = System.currentTimeMillis();

    realChain.eventListener().requestHeadersStart(realChain.call());
    httpCodec.writeRequestHeaders(request);//(1)
    realChain.eventListener().requestHeadersEnd(realChain.call(), request);

    Response.Builder responseBuilder = null;
    if (HttpMethod.permitsRequestBody(request.method()) && request.body() != null) {
      // If there's a "Expect: 100-continue" header on the request, wait for a "HTTP/1.1 100
      // Continue" response before transmitting the request body. If we don't get that, return
      // what we did get (such as a 4xx response) without ever transmitting the request body.
      if ("100-continue".equalsIgnoreCase(request.header("Expect"))) {
        httpCodec.flushRequest();
        realChain.eventListener().responseHeadersStart(realChain.call());
        responseBuilder = httpCodec.readResponseHeaders(true);
      }

      if (responseBuilder == null) {
        // Write the request body if the "Expect: 100-continue" expectation was met.
        realChain.eventListener().requestBodyStart(realChain.call());
        long contentLength = request.body().contentLength();
        CountingSink requestBodyOut =
            new CountingSink(httpCodec.createRequestBody(request, contentLength));
        BufferedSink bufferedRequestBody = Okio.buffer(requestBodyOut);

        request.body().writeTo(bufferedRequestBody);//（2）
        bufferedRequestBody.close();
        realChain.eventListener()
            .requestBodyEnd(realChain.call(), requestBodyOut.successfulCount);
      } else if (!connection.isMultiplexed()) {
        // If the "Expect: 100-continue" expectation wasn't met, prevent the HTTP/1 connection
        // from being reused. Otherwise we're still obligated to transmit the request body to
        // leave the connection in a consistent state.
        streamAllocation.noNewStreams();
      }
    }

    httpCodec.finishRequest();

    if (responseBuilder == null) {
      realChain.eventListener().responseHeadersStart(realChain.call());
      responseBuilder = httpCodec.readResponseHeaders(false);//（3）
    }

    Response response = responseBuilder
        .request(request)
        .handshake(streamAllocation.connection().handshake())
        .sentRequestAtMillis(sentRequestMillis)
        .receivedResponseAtMillis(System.currentTimeMillis())
        .build();

    int code = response.code();
    if (code == 100) {
      // server sent a 100-continue even though we did not request one.
      // try again to read the actual response
      responseBuilder = httpCodec.readResponseHeaders(false);

      response = responseBuilder
              .request(request)
              .handshake(streamAllocation.connection().handshake())
              .sentRequestAtMillis(sentRequestMillis)
              .receivedResponseAtMillis(System.currentTimeMillis())
              .build();

      code = response.code();
    }

    realChain.eventListener()
            .responseHeadersEnd(realChain.call(), response);

//（4）
    if (forWebSocket && code == 101) {
      // Connection is upgrading, but we need to ensure interceptors see a non-null response body.
      response = response.newBuilder()
          .body(Util.EMPTY_RESPONSE)
          .build();
    } else {
      response = response.newBuilder()
          .body(httpCodec.openResponseBody(response))
          .build();
    }

    if ("close".equalsIgnoreCase(response.request().header("Connection"))
        || "close".equalsIgnoreCase(response.header("Connection"))) {
      streamAllocation.noNewStreams();
    }

    if ((code == 204 || code == 205) && response.body().contentLength() > 0) {
      throw new ProtocolException(
          "HTTP " + code + " had non-zero Content-Length: " + response.body().contentLength());
    }

    return response;
  }

/**
     * Return a new Message instance from the global pool. Allows us to
     * avoid allocating new objects in many cases.
     */
    public static Message obtain() {
        synchronized (sPoolSync) {
            if (sPool != null) {
                Message m = sPool;
                sPool = m.next;
                m.next = null;
                m.flags = 0; // clear in-use flag
                sPoolSize--;
                return m;
            }
        }
        return new Message();
    }

/**
    * Returns a new {@link android.os.Message Message} from the global message pool. More efficient than
    * creating and allocating new instances. The retrieved message has its handler set to this instance (Message.target == this).
    *  If you don't want that facility, just call Message.obtain() instead.
    */
   @NonNull
   public final Message obtainMessage()
   {
       return Message.obtain(this);
   }
   
   //Handler.obtainMessage()内部又调用了Message.obtain(handler)
   /**
    * Same as {@link #obtain()}, but sets the value for the <em>target</em> member on the Message returned.
    * @param h  Handler to assign to the returned Message object's <em>target</em> member.
    * @return A Message object from the global pool.
    */
   public static Message obtain(Handler h) {
       Message m = obtain();
       m.target = h;

       return m;
   }

/**
     * User-defined message code so that the recipient can identify
     * what this message is about. Each {@link Handler} has its own name-space
     * for message codes, so you do not need to worry about yours conflicting
     * with other handlers.
     */
    public int what;

/**
     * arg1 and arg2 are lower-cost alternatives to using
     * {@link #setData(Bundle) setData()} if you only need to store a
     * few integer values.
     */
    public int arg1;

    /**
     * arg1 and arg2 are lower-cost alternatives to using
     * {@link #setData(Bundle) setData()} if you only need to store a
     * few integer values.
     */
    public int arg2;

    /**
     * An arbitrary object to send to the recipient.  When using
     * {@link Messenger} to send the message across processes this can only
     * be non-null if it contains a Parcelable of a framework class (not one
     * implemented by the application).   For other data transfer use
     * {@link #setData}.
     *
     * <p>Note that Parcelable objects here are not supported prior to
     * the {@link android.os.Build.VERSION_CODES#FROYO} release.
     */
    public Object obj;

/**
    * The targeted delivery time of this message. The time-base is
    * {@link SystemClock#uptimeMillis}.
    * @hide Only for use within the tests.
    */
    public long when;

Bundle data;

Runnable callback;

boolean enqueueMessage(Message msg, long when) {
        if (msg.target == null) {
            throw new IllegalArgumentException("Message must have a target.");
        }
        if (msg.isInUse()) {
            throw new IllegalStateException(msg + " This message is already in use.");
        }

        synchronized (this) {
            if (mQuitting) {//(1)
                IllegalStateException e = new IllegalStateException(
                        msg.target + " sending message to a Handler on a dead thread");
                Log.w(TAG, e.getMessage(), e);
                msg.recycle();
                return false;
            }

            msg.markInUse();
            msg.when = when;
            Message p = mMessages;
            boolean needWake;
            if (p == null || when == 0 || when < p.when) {
                // New head, wake up the event queue if blocked.
                msg.next = p;
                mMessages = msg;
                needWake = mBlocked;
            } else {
                // Inserted within the middle of the queue.  Usually we don't have to wake
                // up the event queue unless there is a barrier at the head of the queue
                // and the message is the earliest asynchronous message in the queue.
                needWake = mBlocked && p.target == null && msg.isAsynchronous();
                Message prev;
                for (;;) {
                    prev = p;
                    p = p.next;
                    if (p == null || when < p.when) {
                        break;
                    }
                    if (needWake && p.isAsynchronous()) {
                        needWake = false;
                    }
                }
                msg.next = p; // invariant: p == prev.next
                prev.next = msg;
            }

            // We can assume mPtr != 0 because mQuitting is false.
            if (needWake) {
                nativeWake(mPtr);
            }
        }
        return true;
    }

Message next() {
        // Return here if the message loop has already quit and been disposed.
        // This can happen if the application tries to restart a looper after quit
        // which is not supported.
        final long ptr = mPtr;
        if (ptr == 0) {(1)
            return null;
        }

        int pendingIdleHandlerCount = -1; // -1 only during first iteration
        int nextPollTimeoutMillis = 0;
        for (;;) {
            if (nextPollTimeoutMillis != 0) {
                Binder.flushPendingCommands();
            }

            nativePollOnce(ptr, nextPollTimeoutMillis);//(2)

            synchronized (this) {
                // Try to retrieve the next message.  Return if found.
                final long now = SystemClock.uptimeMillis();
                Message prevMsg = null;
                Message msg = mMessages;
                if (msg != null && msg.target == null) {//(3)
                    // Stalled by a barrier.  Find the next asynchronous message in the queue.
                    do {
                        prevMsg = msg;
                        msg = msg.next;
                    } while (msg != null && !msg.isAsynchronous());
                }
                if (msg != null) {
                    if (now < msg.when) {
                        // Next message is not ready.  Set a timeout to wake up when it is ready.
                        nextPollTimeoutMillis = (int) Math.min(msg.when - now, Integer.MAX_VALUE);
                    } else {
                        // Got a message.
                        mBlocked = false;
                        if (prevMsg != null) {
                            prevMsg.next = msg.next;
                        } else {
                            mMessages = msg.next;
                        }
                        msg.next = null;
                        if (DEBUG) Log.v(TAG, "Returning message: " + msg);
                        msg.markInUse();
                        return msg;//(4)
                    }
                } else {
                    // No more messages.
                    nextPollTimeoutMillis = -1;
                }

                // Process the quit message now that all pending messages have been handled.
                if (mQuitting) {
                    dispose();
                    return null;
                }

                // If first time idle, then get the number of idlers to run.
                // Idle handles only run if the queue is empty or if the first message
                // in the queue (possibly a barrier) is due to be handled in the future.
                if (pendingIdleHandlerCount < 0
                        && (mMessages == null || now < mMessages.when)) {
                    pendingIdleHandlerCount = mIdleHandlers.size();
                }
                if (pendingIdleHandlerCount <= 0) {
                    // No idle handlers to run.  Loop and wait some more.
                    mBlocked = true;
                    continue;
                }

                if (mPendingIdleHandlers == null) {
                    mPendingIdleHandlers = new IdleHandler[Math.max(pendingIdleHandlerCount, 4)];
                }
                mPendingIdleHandlers = mIdleHandlers.toArray(mPendingIdleHandlers);
            }

//(5)
            // Run the idle handlers.
            // We only ever reach this code block during the first iteration.
            for (int i = 0; i < pendingIdleHandlerCount; i++) {
                final IdleHandler idler = mPendingIdleHandlers[i];
                mPendingIdleHandlers[i] = null; // release the reference to the handler

                boolean keep = false;
                try {
                    keep = idler.queueIdle();
                } catch (Throwable t) {
                    Log.wtf(TAG, "IdleHandler threw exception", t);
                }

                if (!keep) {
                    synchronized (this) {
                        mIdleHandlers.remove(idler);
                    }
                }
            }

            // Reset the idle handler count to 0 so we do not run them again.
            pendingIdleHandlerCount = 0;

            // While calling an idle handler, a new message could have been delivered
            // so go back and look again for a pending message without waiting.
            nextPollTimeoutMillis = 0;
        }
    }

private int postSyncBarrier(long when) {
        // Enqueue a new sync barrier token.
        // We don't need to wake the queue because the purpose of a barrier is to stall it.
        synchronized (this) {
            final int token = mNextBarrierToken++;
            final Message msg = Message.obtain();
            msg.markInUse();
            msg.when = when;
            msg.arg1 = token;

            Message prev = null;
            Message p = mMessages;
            if (when != 0) {
                while (p != null && p.when <= when) {
                    prev = p;
                    p = p.next;
                }
            }
            if (prev != null) { // invariant: p == prev.next
                msg.next = p;
                prev.next = msg;
            } else {
                msg.next = p;
                mMessages = msg;
            }
            return token;
        }
    }

/** Initialize the current thread as a looper.
     * This gives you a chance to create handlers that then reference
     * this looper, before actually starting the loop. Be sure to call
     * {@link #loop()} after calling this method, and end it by calling
     * {@link #quit()}.
     */
private static void prepare(boolean quitAllowed) {
       if (sThreadLocal.get() != null) {
           throw new RuntimeException("Only one Looper may be created per thread");
       }
       sThreadLocal.set(new Looper(quitAllowed));
   }
   
   //构造方法
    private Looper(boolean quitAllowed) {（1）
       mQueue = new MessageQueue(quitAllowed);
       mThread = Thread.currentThread();
   }

/**
     * Run the message queue in this thread. Be sure to call
     * {@link #quit()} to end the loop.
     */
    public static void loop() {
        final Looper me = myLooper();
        if (me == null) {
            throw new RuntimeException("No Looper; Looper.prepare() wasn't called on this thread.");
        }
        final MessageQueue queue = me.mQueue;

        // Make sure the identity of this thread is that of the local process,
        // and keep track of what that identity token actually is.
        Binder.clearCallingIdentity();
        final long ident = Binder.clearCallingIdentity();

        // Allow overriding a threshold with a system prop. e.g.
        // adb shell 'setprop log.looper.1000.main.slow 1 && stop && start'
        final int thresholdOverride =
                SystemProperties.getInt("log.looper."
                        + Process.myUid() + "."
                        + Thread.currentThread().getName()
                        + ".slow", 0);

        boolean slowDeliveryDetected = false;

        for (;;) {//（1）
            Message msg = queue.next(); // might block
            if (msg == null) {
                // No message indicates that the message queue is quitting.
                return;
            }

            // This must be in a local variable, in case a UI event sets the logger
            final Printer logging = me.mLogging;
            if (logging != null) {
                logging.println(">>>>> Dispatching to " + msg.target + " " +
                        msg.callback + ": " + msg.what);
            }
            // Make sure the observer won't change while processing a transaction.
            final Observer observer = sObserver;

            final long traceTag = me.mTraceTag;
            long slowDispatchThresholdMs = me.mSlowDispatchThresholdMs;
            long slowDeliveryThresholdMs = me.mSlowDeliveryThresholdMs;
            if (thresholdOverride > 0) {
                slowDispatchThresholdMs = thresholdOverride;
                slowDeliveryThresholdMs = thresholdOverride;
            }
            final boolean logSlowDelivery = (slowDeliveryThresholdMs > 0) && (msg.when > 0);
            final boolean logSlowDispatch = (slowDispatchThresholdMs > 0);

            final boolean needStartTime = logSlowDelivery || logSlowDispatch;
            final boolean needEndTime = logSlowDispatch;

            if (traceTag != 0 && Trace.isTagEnabled(traceTag)) {
                Trace.traceBegin(traceTag, msg.target.getTraceName(msg));
            }

            final long dispatchStart = needStartTime ? SystemClock.uptimeMillis() : 0;
            final long dispatchEnd;
            Object token = null;
            if (observer != null) {
                token = observer.messageDispatchStarting();
            }
            long origWorkSource = ThreadLocalWorkSource.setUid(msg.workSourceUid);
            try {
                msg.target.dispatchMessage(msg);//（2)
                if (observer != null) {
                    observer.messageDispatched(token, msg);
                }
                dispatchEnd = needEndTime ? SystemClock.uptimeMillis() : 0;
            } catch (Exception exception) {
                if (observer != null) {
                    observer.dispatchingThrewException(token, msg, exception);
                }
                throw exception;
            } finally {
                ThreadLocalWorkSource.restore(origWorkSource);
                if (traceTag != 0) {
                    Trace.traceEnd(traceTag);
                }
            }
            if (logSlowDelivery) {
                if (slowDeliveryDetected) {
                    if ((dispatchStart - msg.when) <= 10) {
                        Slog.w(TAG, "Drained");
                        slowDeliveryDetected = false;
                    }
                } else {
                    if (showSlowLog(slowDeliveryThresholdMs, msg.when, dispatchStart, "delivery",
                            msg)) {
                        // Once we write a slow delivery log, suppress until the queue drains.
                        slowDeliveryDetected = true;
                    }
                }
            }
            if (logSlowDispatch) {
                showSlowLog(slowDispatchThresholdMs, dispatchStart, dispatchEnd, "dispatch", msg);
            }

            if (logging != null) {
                logging.println("<<<<< Finished to " + msg.target + " " + msg.callback);
            }

            // Make sure that during the course of dispatching the
            // identity of the thread wasn't corrupted.
            final long newIdent = Binder.clearCallingIdentity();
            if (ident != newIdent) {
                Log.wtf(TAG, "Thread identity changed from 0x"
                        + Long.toHexString(ident) + " to 0x"
                        + Long.toHexString(newIdent) + " while dispatching to "
                        + msg.target.getClass().getName() + " "
                        + msg.callback + " what=" + msg.what);
            }

            msg.recycleUnchecked();//(3)
        }
    }

/**
    public boolean sendMessageAtTime(@NonNull Message msg, long uptimeMillis) {
        MessageQueue queue = mQueue;
        if (queue == null) {
            RuntimeException e = new RuntimeException(
                    this + " sendMessageAtTime() called with no mQueue");
            Log.w("Looper", e.getMessage(), e);
            return false;
        }
        return enqueueMessage(queue, msg, uptimeMillis);
    }
    
    private boolean enqueueMessage(@NonNull MessageQueue queue, @NonNull Message msg,
            long uptimeMillis) {
        msg.target = this;
        msg.workSourceUid = ThreadLocalWorkSource.getUid();

        if (mAsynchronous) {
            msg.setAsynchronous(true);
        }
        return queue.enqueueMessage(msg, uptimeMillis);
    }

/**
    * Remove any pending posts of callbacks and sent messages whose
    * <var>obj</var> is <var>token</var>.  If <var>token</var> is null,
    * all callbacks and messages will be removed.
    */
   public final void removeCallbacksAndMessages(@Nullable Object token) {
       mQueue.removeCallbacksAndMessages(this, token);
   }
   
   //MessageQueue.removeCallbacksAndMessages
    void removeCallbacksAndMessages(Handler h, Object object) {
       if (h == null) {
           return;
       }

       synchronized (this) {
           Message p = mMessages;

           // Remove all messages at front.
           while (p != null && p.target == h
                   && (object == null || p.obj == object)) {
               Message n = p.next;
               mMessages = n;
               p.recycleUnchecked();
               p = n;
           }

           // Remove all messages after front.
           while (p != null) {
               Message n = p.next;
               if (n != null) {
                   if (n.target == h && (object == null || n.obj == object)) {
                       Message nn = n.next;
                       n.recycleUnchecked();
                       p.next = nn;
                       continue;
                   }
               }
               p = n;
           }
       }
   }

void scheduleTraversals() {
       if (!mTraversalScheduled) {
           mTraversalScheduled = true;
           mTraversalBarrier = mHandler.getLooper().getQueue().postSyncBarrier();
           mChoreographer.postCallback(
                   Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);
           if (!mUnbufferedInputDispatch) {
               scheduleConsumeBatchedInput();
           }
           notifyRendererOfFramePending();
           pokeDrawLockIfNeeded();
       }
   }

private static final int MODE_SHIFT = 30;
private static final int MODE_MASK  = 0x3 << MODE_SHIFT;

 /**
 * Measure specification mode: The parent has not imposed any constraint
 * on the child. It can be whatever size it wants.
 */
public static final int UNSPECIFIED = 0 << MODE_SHIFT;

/**
 * Measure specification mode: The parent has determined an exact size
 * for the child. The child is going to be given those bounds regardless
 * of how big it wants to be.
 */
public static final int EXACTLY     = 1 << MODE_SHIFT;

/**
 * Measure specification mode: The child can be as large as it wants up
 * to the specified size.
 */
public static final int AT_MOST     = 2 << MODE_SHIFT;

public static int makeMeasureSpec(@IntRange(from = 0, to = (1 << MeasureSpec.MODE_SHIFT) - 1) int size,
                                  @MeasureSpecMode int mode) {
    if (sUseBrokenMakeMeasureSpec) {
        return size + mode;
    } else {
        return (size & ~MODE_MASK) | (mode & MODE_MASK);
    }
}

@MeasureSpecMode
public static int getMode(int measureSpec) {
    //noinspection ResourceType
    return (measureSpec & MODE_MASK);
}

public static int getSize(int measureSpec) {
    return (measureSpec & ~MODE_MASK);
}