# 4.5: Exercise 4

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In the repository for this book you’ll find the source files you need for this exercise:

1. Profiler.java contains the implementation of the Profiler class described above. You will use this class, but you don’t have to know how it works. But feel free to read the source.
2. ProfileListAdd.java contains starter code for this exercise, including the example, above, which profiles ArrayList.add. You will modify this file to profile a few other methods.

Also, in the code directory, you’ll find the Ant build file build.xml.

Run ant ProfileListAdd to run ProfileListAdd.java. You should get results similar to Figure 4.4.1, but you might have to adjust startN or endMillis. The estimated slope should be close to 1, indicating that performing n add operations takes time proportional to n raised to the exponent 1; that is, it is in $$O(n)$$.

In ProfileListAdd.java, you’ll find an empty method named profileArrayListAddBeginning. Fill in the body of this method with code that tests ArrayList.add, always putting the new element at the beginning. If you start with a copy of profileArrayListAddEnd, you should only have to make a few changes. Add a line in main to invoke this method.

Run ant ProfileListAdd again and interpret the results. Based on our understanding of how ArrayList works, we expect each add operation to be linear, so the total time for n adds should be quadratic. If so, the estimated slope of the line, on a log-log scale, should be near 2. Is it?

Now let’s compare that to the performance of LinkedList. Fill in the body of profileLinkedListAddBeginning and use it to classify LinkedList.add when we put the new element at the beginning. What performance do you expect? Are the results consistent with your expectations?

Finally, fill in the body of profileLinkedListAddEnd and use it to classify LinkedList.add when we put the new element at the end. What performance do you expect? Are the results consistent with your expectations?

I’ll present results and answer these questions in the next chapter.

This page titled 4.5: Exercise 4 is shared under a CC BY-NC-SA 3.0 license and was authored, remixed, and/or curated by Allen B. Downey (Green Tea Press) .