@Override
  public boolean equals(Object obj) {
    if (!(obj instanceof ExtensionResponse)) {
      return false;
    }
    if (this == obj) {
      return true;
    }
    ExtensionResponse extensionResponse = (ExtensionResponse) obj;
    return getExtensionName().equals(extensionResponse.getExtensionName());
  }
An extension version is like a stack version but it contains custom services.  Linking an extension
version to the current stack version allows the cluster to install the custom services contained in
the extension version.
ambari-server/src/main/java/org/apache/ambari/server/controller/ExtensionResponse.java