diff --git a/src/main/java/Model/ExchangeObserver.java b/src/main/java/Model/ExchangeObserver.java
new file mode 100644
index 0000000..ad3f6a5
--- /dev/null
+++ b/src/main/java/Model/ExchangeObserver.java
@@ -0,0 +1,16 @@
+package Model;
+
+/**
+ * Observer interface for the Exchange subject.
+ * Implement this interface to receive notifications whenever the exchange
+ * state changes (week advances, a trade is committed).
+ */
+public interface ExchangeObserver {
+
+    /**
+     * Called by the Exchange after its state has changed.
+     *
+     * @param exchange the Exchange that triggered the notification
+     */
+    void onExchangeUpdated(Exchange exchange);
+}
diff --git a/target/maven-status/maven-compiler-plugin/compile/default-compile/inputFiles.lst b/target/maven-status/maven-compiler-plugin/compile/default-compile/inputFiles.lst
index fc20747..f40803d 100644
--- a/target/maven-status/maven-compiler-plugin/compile/default-compile/inputFiles.lst
+++ b/target/maven-status/maven-compiler-plugin/compile/default-compile/inputFiles.lst
@@ -1,5 +1,6 @@
 C:\Users\elisa\Downloads\progdel1\Programmering2_mappe_v26\src\main\java\Controller\StockFileHandler.java
 C:\Users\elisa\Downloads\progdel1\Programmering2_mappe_v26\src\main\java\Model\Exchange.java
+C:\Users\elisa\Downloads\progdel1\Programmering2_mappe_v26\src\main\java\Model\ExchangeObserver.java
 C:\Users\elisa\Downloads\progdel1\Programmering2_mappe_v26\src\main\java\Model\Player.java
 C:\Users\elisa\Downloads\progdel1\Programmering2_mappe_v26\src\main\java\Model\Portfolio.java
 C:\Users\elisa\Downloads\progdel1\Programmering2_mappe_v26\src\main\java\Model\Purchase.java