Java 泛型理解

//泛型限制仅对对象的引用有效，即等式的左边部分
ArrayList<String> stringList1 = new ArrayList<String>();
//等式右边只是在堆空间中申请内存,因此可以简写为如下
ArrayList<String> stringList2 = new ArrayList<>();
//反过来引用不使用泛型限定的情况下, 等式右边的泛型不会起到任何作用
//容器依然能存入任何对象
ArrayList stringList3 = new ArrayList<String>();

public static <T extends Comparable> T get(T t1,T t2) { //添加类型限定  
        if(t1.compareTo(t2)>=0);  
        return t1;  
    }

package retrofit2;

import java.lang.annotation.Annotation;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;

/**
 * Adapts a {@link Call} into the type of {@code T}. Instances are created by {@linkplain Factory a
 * factory} which is {@linkplain Retrofit.Builder#addCallAdapterFactory(Factory) installed} into
 * the {@link Retrofit} instance.
 */
public interface CallAdapter<T> {
  /**
   * Returns the value type that this adapter uses when converting the HTTP response body to a Java
   * object. For example, the response type for {@code Call<Repo>} is {@code Repo}. This type
   * is used to prepare the {@code call} passed to {@code #adapt}.
   * <p>
   * Note: This is typically not the same type as the {@code returnType} provided to this call
   * adapter's factory.
   */
  Type responseType();

  /**
   * Returns an instance of {@code T} which delegates to {@code call}.
   * <p>
   * For example, given an instance for a hypothetical utility, {@code Async}, this instance would
   * return a new {@code Async<R>} which invoked {@code call} when run.
   * <pre>{@code
   * @Override
   * public <R> Async<R> adapt(final Call<R> call) {
   *   return Async.create(new Callable<Response<R>>() {
   *     @Override
   *     public Response<R> call() throws Exception {
   *       return call.execute();
   *     }
   *   });
   * }
   * }</pre>
   */
  <R> T adapt(Call<R> call);

  /**
   * Creates {@link CallAdapter} instances based on the return type of {@linkplain
   * Retrofit#create(Class) the service interface} methods.
   */
  abstract class Factory {
    /**
     * Returns a call adapter for interface methods that return {@code returnType}, or null if it
     * cannot be handled by this factory.
     */
    public abstract CallAdapter<?> get(Type returnType, Annotation[] annotations,
        Retrofit retrofit);

    /**
     * Extract the upper bound of the generic parameter at {@code index} from {@code type}. For
     * example, index 1 of {@code Map<String, ? extends Runnable>} returns {@code Runnable}.
     */
    protected static Type getParameterUpperBound(int index, ParameterizedType type) {
      return Utils.getParameterUpperBound(index, type);
    }

    /**
     * Extract the raw class type from {@code type}. For example, the type representing
     * {@code List<? extends Runnable>} returns {@code List.class}.
     */
    protected static Class<?> getRawType(Type type) {
      return Types.getRawType(type);
    }
  }
}