Merge pull request #1789 from benjchristensen/1668-groupedObservable

GroupedObservable.from/create

Author: benjchristensen

src/main/java/rx/internal/operators/OperatorGroupBy.java

@@ -188,7 +188,7 @@ public void onNext(T t) {
         private GroupState<K, T> createNewGroup(final K key) {
             final GroupState<K, T> groupState = new GroupState<K, T>();
 
-            GroupedObservable<K, R> go = new GroupedObservable<K, R>(key, new OnSubscribe<R>() {
+            GroupedObservable<K, R> go = GroupedObservable.create(key, new OnSubscribe<R>() {
 
                 @Override
                 public void call(final Subscriber<? super R> o) {

src/main/java/rx/observables/GroupedObservable.java

@@ -16,15 +16,16 @@
 package rx.observables;
 
 import rx.Observable;
+import rx.Scheduler;
+import rx.Subscriber;
 import rx.functions.Func1;
 
 /**
- * An {@link Observable} that has been grouped by key, the value of which can be obtained with
- * {@link #getKey()}.
+ * 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
+ * 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}{@code (0)} to them.
  * 
  * @param <K>
@@ -37,7 +38,58 @@
 public class GroupedObservable<K, T> extends Observable<T> {
     private final K key;
 
-    public GroupedObservable(K key, OnSubscribe<T> onSubscribe) {
+    /**
+     * Converts an {@link Observable} into a {@code GroupedObservable} with a particular key.
+     *
+     * @param key
+     *            the key to identify the group of items emitted by this {@code GroupedObservable}
+     * @param o
+     *            the {@link Observable} to convert
+     * @return a {@code GroupedObservable} representation of {@code o}, with key {@code key}
+     */
+    public static <K, T> GroupedObservable<K, T> from(K key, final Observable<T> o) {
+        return new GroupedObservable<K, T>(key, new OnSubscribe<T>() {
+
+            @Override
+            public void call(Subscriber<? super T> s) {
+                o.unsafeSubscribe(s);
+            }
+        });
+    }
+
+    /**
+     * Returns an Observable that will execute the specified function when a {@link Subscriber} subscribes to
+     * it.
+     * <p>
+     * <img width="640" height="200" src="https://raw.github.com/wiki/ReactiveX/RxJava/images/rx-operators/create.png" alt="">
+     * <p>
+     * Write the function you pass to {@code create} so that it behaves as an Observable: It should invoke the
+     * Subscriber's {@link Subscriber#onNext onNext}, {@link Subscriber#onError onError}, and {@link Subscriber#onCompleted onCompleted} methods appropriately.
+     * <p>
+     * A well-formed Observable must invoke either the Subscriber's {@code onCompleted} method exactly once or
+     * its {@code onError} method exactly once.
+     * <p>
+     * See <a href="http://go.microsoft.com/fwlink/?LinkID=205219">Rx Design Guidelines (PDF)</a> for detailed
+     * information.
+     * <dl>
+     * <dt><b>Scheduler:</b></dt>
+     * <dd>{@code create} does not operate by default on a particular {@link Scheduler}.</dd>
+     * </dl>
+     * 
+     * @param <K>
+     *            the type of the key
+     * @param <T>
+     *            the type of the items that this Observable emits
+     * @param f
+     *            a function that accepts an {@code Subscriber<T>}, and invokes its {@code onNext}, {@code onError}, and {@code onCompleted} methods as appropriate
+     * @return a GroupedObservable that, when a {@link Subscriber} subscribes to it, will execute the specified
+     *         function
+     */
+    public final static <K, T> GroupedObservable<K, T> create(K key, OnSubscribe<T> f) {
+        return new GroupedObservable<K, T>(key, f);
+    }
+
+    protected GroupedObservable(K key, OnSubscribe<T> onSubscribe) {
         super(onSubscribe);
         this.key = key;
     }