1 files changed, 25 insertions, 0 deletions
diff --git a/src/com/vaadin/terminal/AbstractExtension.java b/src/com/vaadin/terminal/AbstractExtension.java
new file mode 100644
index 0000000000..d01f7544c5
--- /dev/null
+++ b/src/com/vaadin/terminal/AbstractExtension.java
@@ -0,0 +1,25 @@
+package com.vaadin.terminal;
+
+import com.vaadin.terminal.gwt.server.ClientConnector;
+
+public abstract class AbstractExtension extends AbstractClientConnector implements
+        Extension {
+
+    protected Class<? extends ClientConnector> getAcceptedParentType() {
+        return ClientConnector.class;
+    }
+
+    @Override
+    public void setParent(ClientConnector parent) {
+        Class<? extends ClientConnector> acceptedParentType = getAcceptedParentType();
+        if (parent == null || acceptedParentType.isInstance(parent)) {
+            super.setParent(parent);
+        } else {
+            throw new IllegalArgumentException(getClass().getName()
+                    + " can only be attached to parents of type "
+                    + acceptedParentType.getName() + " but attach to "
+                    + parent.getClass().getName() + " was attempted.");
+        }
+    }
+
+}