I removed buttons the "get more letters", and "do not repeat anymore" buttons because their function is not intuitive. They would confuse users, and explaining their use is not valuable. Instead of using those buttons to introduce new letters for the user, the program will choose letters randomly. I removed highlighting for newly introduced Audio visual units. I also removed the feedback on the label telling the user if they were correct or incorrect, because it occurs at the same time as a new letter is introduced, which is confusing and distracting.
Refactoring by organizing imports (specifying exact types instead of using wild cards). No change in functionality.
Formatted whitespace in source code using Eclipse IDE. The format I used has been exported into the code_format/format.xml path and is included in this commit.