https://github.com/ReactiveX/RxJava: Reactive Extensions for Java
  • David Karnok 
Copyright (c) 2016-present, RxJava Contributors.
Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
compliance with the License. You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software distributed under the License is
distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
the License for the specific language governing permissions and limitations under the License.

/**
 * Copyright (c) 2016-present, RxJava Contributors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in
 * compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License is
 * distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See
 * the License for the specific language governing permissions and limitations under the License.
 */
package io.reactivex.observables;

import io.reactivex.Observable;
import io.reactivex.annotations.Nullable;


An Observable that has been grouped by key, the value of which can be obtained with getKey(). 

Note: A GroupedObservable will cache the items it is to emit until such time as it is subscribed to. For this reason, in order to avoid memory leaks, you should not simply ignore those GroupedObservables that do not concern you. Instead, you can signal to them that they may discard their buffers by applying an operator like take(0) to them. 
Type parameters:
  • <K> – 
           the type of the key
  • <T> –  the type of the items emitted by the GroupedObservable
See Also:
/**
 * An {@link Observable} that has been grouped by key, the value of which can be obtained with {@link #getKey()}.
 * <p>
 * <em>Note:</em> A {@link GroupedObservable} will cache the items it is to emit until such time as it
 * is subscribed to. For this reason, in order to avoid memory leaks, you should not simply ignore those
 * {@code GroupedObservable}s that do not concern you. Instead, you can signal to them that they
 * may discard their buffers by applying an operator like {@link Observable#take take}{@code (0)} to them.
 *
 * @param <K>
 *            the type of the key
 * @param <T>
 *            the type of the items emitted by the {@code GroupedObservable}
 * @see Observable#groupBy(io.reactivex.functions.Function)
 * @see <a href="http://reactivex.io/documentation/operators/groupby.html">ReactiveX documentation: GroupBy</a>
 */
public abstract class GroupedObservable<K, T> extends Observable<T> {

    final K key;

    
Constructs a GroupedObservable with the given key.

Params:
  • key – the key
/**
     * Constructs a GroupedObservable with the given key.
     * @param key the key
     */
    protected GroupedObservable(@Nullable K key) {
        this.key = key;
    }

    
Returns the key that identifies the group of items emitted by this GroupedObservable. 
Returns:the key that the items emitted by this GroupedObservable were grouped by
/**
     * Returns the key that identifies the group of items emitted by this {@code GroupedObservable}.
     *
     * @return the key that the items emitted by this {@code GroupedObservable} were grouped by
     */
    @Nullable
    public K getKey() {
        return key;
    }
}