4.6 Java4040: purpose of framework implementations and algorithms  (Page 5/6)

Time required to search theTreeSet collection

The time required to find the test value in the TreeSet object was so small that it wasn't even measurable within the granularity of thesystem clock (other experiments have caused me to believe that the granularity of the system clock on this machine is at least sixteen milliseconds) . Hence, the original reported time required to find the test value in the TreeSet object was zero.

In order to get a measurable time value to search the TreeSet object, I had to wrap the invocation of the contains method in a for-loop and search for the same value 100,000 times in succession. Thus, the time required tofind the test value in the TreeSet object was approximately 0.00030 milliseconds as compared to 100 milliseconds for the ArrayList object.

(I'll let you do the arithmetic to see if this makes sense in terms of the expected time cost to search the two different types of collections. Don't forgetthe extra overhead of the for-loop.)

Different implementations

This is a graphic demonstration that even though both objects can be treated as type Collection , and the contains method can be called on either object in a polymorphic manner, the actual implementations of the twoobjects and the implementations of the contains methods in those two objects are different.

Each type of collection has advantages and disadvantages, depending on your needs.

Polymorphic behavior applies

The important point is that if you receive a reference to the collection object as type Collection , you can call the contains method on that reference without regard to the underlying structure of the collection object.This is because polymorphic behavior applies.

Very briefly, polymorphic behavior means that the actual method that is executed is the appropriate method for that type of object regardless of theactual type (class) of the reference to the object. This is one of the great advantages of using the Java Collections Framework and passing collection objects amongmethods as interface types.

Sorting algorithms

Some of the implementations of the Java Collection Framework maintain their elements in a random order, and other implementations maintain their elements ina sorted order. Thus, the framework also provides sorting algorithms. However, the sorting algorithms used to maintain the order of the collections are notexposed in the way that the search algorithm is exposed (via the contains method). Rather, the sorting algorithms are implicit in those implementations that need them, and are absent from those implementations thatdon't need them.

Now for a little quiz

Let's see if you are still awake. Select the words in one pair of parentheses in the following statement that causes the statement to be true.

The interfaces in the Collections Framework make it possible to manipulate the contents of collections in a manner that is (dependent on)(independent of) the underlying implementation of each collection.

And the answer is ...

The interfaces in the Collections Framework make it possible to manipulate the contents of collections in a manner that is independent of the underlying implementation of each collection. That is the beauty of basing the framework oninterfaces that declare polymorphic methods.