Synchronized implementation of ISubject with pull capabilities

1 files changed, 45 insertions, 0 deletions

diff --git a/main/src/cgeo/geocaching/utils/MemorySubject.java b/main/src/cgeo/geocaching/utils/MemorySubject.java
new file mode 100644
index 0000000..2720fc6
--- /dev/null
+++ b/main/src/cgeo/geocaching/utils/MemorySubject.java
@@ -0,0 +1,45 @@
+package cgeo.geocaching.utils;
+
+/**
+ * Synchronized implementation of the {@link ISubject} interface with an added pull interface.
+ *
+ * @param <T>
+ *         the kind of data to observe
+ */
+public class MemorySubject<T> extends Subject<T> {
+
+    /**
+     * The latest version of the observed data.
+     * <p/>
+     * A child class implementation may want to set this field from its constructors, in case early observers request
+     * the data before it got a chance to get updated. Otherwise, <code>null</code> will be returned until updated
+     * data is available.
+     */
+    protected T memory;
+
+    @Override
+    public synchronized boolean addObserver(final IObserver<? super T> observer) {
+        final boolean added = super.addObserver(observer);
+        if (added && memory != null) {
+            observer.update(memory);
+        }
+        return added;
+    }
+
+    @Override
+    public synchronized boolean notifyObservers(final T data) {
+        memory = data;
+        return super.notifyObservers(data);
+    }
+
+    /**
+     * Get the memorized version of the data.
+     *
+     * @return the initial data set by the subject (which may be <code>null</code>),
+     *         or the updated data if it is available
+     */
+    public T getMemory() {
+        return memory;
+    }
+
+}