Does a programmer need to write every class he or she uses? Why or why not?

What will be an ideal response?

The same programmer does not need to write every class he or she uses. Often, you will write programs that use classes created by others. For example, many programs you have seen so far in this book have used the System class. You did not have to create it or its println() method; both were provided for you by Java's creators. Similarly, you might create a class that others will use to instantiate objects within their own applications.