Behavior of the program:

Generally speaking, this program

• Instantiates a new visual object that extends the JFrame class and contains a JSlider object.
• Instantiates Picture objects from two image files (beach and butterfly) along with some blank Picture objects of the same size.
• Defines a method named setOpacity that can be called to set the opacity of every pixel in a picture to a specified value.
• Defines a method named drawPictureOnPicture that can be called to draw one picture onto another picture.
• Registers a ChangeEvent handler on the slider to:
  • Extract a percent-opacity value from the slider based on the position of the thumb.
  • Apply that opacity value to the butterfly image.
  • Draw the modified butterfly image on the beach image and display it.