I peformed the following actions:

1) I removed all direct references in this game of the constants DEFAULT_CANVAS_WIDTH and DEFAULT_CANVAS_HEIGHT from the class GameEngineConstants. These direct references are only used in the Game.java file, which is used to create the space invaders game and corresponding JFrame application.

2) I removed all constant declarations from other source files (e.g., PlayerEntity.java, UFOEntity.java, etc...) and placed them in the source file SIConstants.java.