in java plz explain

P13.2 Phone numbers and PIN codes can be easier to remember when you find words that spell out the number on a standard phone pad. For example, instead of remembering the combination 5282, you can just think of JAVA. Write a recursive method that, given a number, yields all possible spellings (which may or may not be real words). P13.3 Continue Exercise P13.2, checking the words against the /usr/share/dict/words file on your computer, or the words.txt file in the companion code for this book. For a given number, return only actual words. ... P13.4 With a longer number, you may need more than one word to remember it on a phone pad. For example, 263-346- 5282 is CODE IN JAVA. Using your work from Exercise .. P13.3, write a program that, given any number, lists all word sequences that spell the number on a phone pad