DataSubscriptionList: add clears canceled state, java docs

Author: greenrobot

objectbox-java/src/main/java/io/objectbox/reactive/DataSubscriptionList.java

@@ -1,15 +1,28 @@
 package io.objectbox.reactive;
 
+import java.util.ArrayList;
 import java.util.List;
 
+/**
+ * Tracks any number of {@link DataSubscription} objects, which can be canceled with a single {@link #cancel()} call.
+ * This is typically used in live cycle components like Android's Activity:
+ * <ul>
+ * <li>Make DataSubscriptionList a field</li>
+ * <li>Call {@link #add(DataSubscription)} during onStart/onResume for each subscription</li>
+ * <li>Call {@link #cancel()} during onStop/onPause</li>
+ * </ul>
+ */
 public class DataSubscriptionList implements DataSubscription {
+    private final List<DataSubscription> subscriptions = new ArrayList<>();
     private boolean canceled;
-    List<DataSubscription> subscriptions;
 
+    /** Add the given subscription to the list of tracked subscriptions. Clears any previous "canceled" state. */
     public synchronized void add(DataSubscription subscription) {
         subscriptions.add(subscription);
+        canceled = false;
     }
 
+    /** Cancels all tracked subscriptions and removes all references to them. */
     @Override
     public synchronized void cancel() {
         canceled = true;
@@ -19,11 +32,13 @@ public synchronized void cancel() {
         subscriptions.clear();
     }
 
+    /** Returns true if {@link #cancel()} was called without any subsequent calls to {@link #add(DataSubscription)}. */
     @Override
     public synchronized boolean isCanceled() {
         return canceled;
     }
 
+    /** Returns number of active (added) subscriptions (resets to 0 after {@link #cancel()}). */
     public synchronized int getActiveSubscriptionCount() {
         return subscriptions.size();
     }