Friday, September 17, 2010

Code to Understand Objective 6.1

Courtesy of SCJP Sun® Certified Programmer for Java™ 6 Study Guide Exam (310-065) (9780071591065)
Courtesy of

6.1 Given a design scenario, determine which collection classes and/or interfaces should be used to properly implement that design, including the use of the Comparable interface.

There are two ways to traverse collections:

(1) with the for-each construct

(2) by using Iterators

The following program takes the words in its argument list and prints out any duplicate words, the number of distinct words, and a list of the words with duplicates eliminated.

Note that the code always refers to the Collection by its interface type (Set) rather than by its implementation type (HashSet). This is a strongly recommended programming practice because it gives you the flexibility to change implementations merely by changing the constructor.

If you want the program to print the word list in alphabetical order, merely change the Set's implementation type from HashSet to TreeSet.

To calculate the union, intersection, or set difference of two sets nondestructively (without modifying either set), the caller must copy one set before calling the appropriate bulk operation. The following are the resulting idioms.

Let's revisit the FindDups program. Suppose you want to know which words in the argument list occur only once and which occur more than once, but you do not want any duplicates printed out repeatedly. This effect can be achieved by generating two sets — one containing every word in the argument list and the other containing only the duplicates. The words that occur only once are the set difference of these two sets, which we know how to compute. Here's how the resulting program looks.

Produce a third List consisting of the second list appended to the first.

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