You should assume that the file is too big to attempt to read it into an array. In figure 15.6, the file-opening code happens to be located in the constructor method. It could be placed elsewhere in your program. The search word typed by the user might include extraneous spaces, capitalization oddities, etc. that can easily be cleaned up before searching for that word in the dictionary. Similarly, remember that the words in the input file have been padded with spaces to length 6.
Spaces definitely count when making comparisons between two strings using the equals method.
This would require writing a new copy of the file.