Question

All,

I am working on an existing system where the developer had defined a lot of HashMaps with following definition:

HashMap<String, Comparable> x = new HashMap<String, Comparable>();

Now, there is absolutely no need of comparison for the value part of the hashmap since it simply represents only a single piece of information. The developer used Comparable since the only expected values were String and int types(converted to Integer object) and the developer assumed the best way to store both data types is using Comparable interface.

So, I went ahead and changed the code since there was no point of comparison here by defining the HashMap as:

HashMap<String, Object> y = new HashMap<String, Object>();

I had timed the code execution for before and after change. I am a bit surprised as to why the code is taking more time to execute after my changes were deployed (though not a performance bottleneck currently).

Can anyone please help me understand the change in behavior due to my code updates?

Answer 1

Both are identical in terms of performance as the value is not used for hashing (only the key is).

How are you timing your code? Make sure you time each test case separately. Do not do the following as the second test will have the benefit of the first test having “warmed-up” the JVM. My guess is that your test is flawed or you’re seeing normal execution time variations.

public static void main(String[] args) {
    for loop {
        test HashMap<String, Comparable>
    }

    for loop {
        test HashMap<String, Object>
    }
}