在 RxJava 中，Emitter 接口和 Observer 接口有什么区别？两者都有相同的方法
public interface Emitter<@NonNull T> {
/**
* Signal a normal value.
* @param value the value to signal, not {@code null}
*/
void onNext(@NonNull T value);
/**
* Signal a {@link Throwable} exception.
* @param error the {@code Throwable} to signal, not {@code null}
*/
void onError(@NonNull Throwable error);
/**
* Signal a completion.
*/
void onComplete();
}
public interface Observer<@NonNull T> {
/**
* Provides the {@link Observer} with the means of cancelling (disposing) the
* connection (channel) with the {@link Observable} in both
* synchronous (from within {@link #onNext(Object)}) and asynchronous manner.
* @param d the {@link Disposable} instance whose {@link Disposable#dispose()} can
* be called anytime to cancel the connection
* @since 2.0
*/
void onSubscribe(@NonNull Disposable d);
/**
* Provides the {@link Observer} with a new item to observe.
* <p>
* The {@link Observable} may call this method 0 or more times.
* <p>
* The {@code Observable} will not call this method again after it calls either {@link #onComplete} or
* {@link #onError}.
*
* @param t
* the item emitted by the Observable
*/
void onNext(@NonNull T t);
/**
* Notifies the {@link Observer} that the {@link Observable} has experienced an error condition.
* <p>
* If the {@code Observable} calls this method, it will not thereafter call {@link #onNext} or
* {@link #onComplete}.
*
* @param e
* the exception encountered by the Observable
*/
void onError(@NonNull Throwable e);
/**
* Notifies the {@link Observer} that the {@link Observable} has finished sending push-based notifications.
* <p>
* The {@code Observable} will not call this method if it calls {@link #onError}.
*/
void onComplete();
}