src/java.desktop/macosx/classes/sun/lwawt/macosx/CPlatformWindow.java

*** 1072,1081 ****
--- 1072,1088 ----
          if (peer != null) {
              peer.notifyNCMouseDown();
          }
      }
  
+     /* Do toggle full screen upon double click
+      * on non-client area(i.e., title bar)
+      */
+     private void deliverNCDblClick() {
+         execute(this::_toggleFullScreenMode);
+     }
+ 
      /*
       * Our focus model is synthetic and only non-simple window
       * may become natively focusable window.
       */
      private boolean isNativelyFocusableWindow() {