Equivalence#Wrapper<T>

public static final class Wrapper<T> implements Serializable {  省去了部分不重要函数

  private final Equivalence<? super T> equivalence;  包装的equivalence实例，用于判别两个对象是否相等
  @Nullable private final T reference;                    具体类型，注意加了final关键字
  private Wrapper(Equivalence<? super T> equivalence, @Nullable T reference) {  //构造函数,为private,这样你就只能通过equivalence中的函数构造Wrapper
    this.equivalence = checkNotNull(equivalence);
    this.reference = reference;
                                       
  public boolean equals(@Nullable Object obj) {
    if (obj == this) {
      return true;
    }
    if (obj instanceof Wrapper) {  这就是我为什么说只有俩个Wapper比较才有意义
      Wrapper<?> that = (Wrapper<?>) obj; // note: not necessarily a Wrapper<T>

      if (this.equivalence.equals(that.equivalence)) {  主要是考虑如果a==b，那么反之也应该b==a;如果b!=a.这种情况返回false;
        @SuppressWarnings("unchecked")
        Equivalence<Object> equivalence = (Equivalence<Object>) this.equivalence;
        return equivalence.equivalent(this.reference, that.reference);
      }
    }
    return false;
  }
  private static final long serialVersionUID = 0;
}