Look in the API
doc for the classes that are not being found. The API doc for the java SE classes is here:
http://docs.oracle.com/javase/8/docs/api/index.html
Scan in the lower left of the page for the classname, click on it and its API doc will be shown in the main frame.
The class's package is shown near the top of the page.
An example from the API doc for the BufferedImage class the packages are in bold:
java.awt.image
Class BufferedImage
java.lang.Object
java.awt.Image
java.awt.image.BufferedImage