Java – why is HashMap faster than HashSet?

I've been reading / searching why HashMap is faster than HashSet

I am not familiar with the following statement

>HashMap is faster than HashSet because these values are associated with unique keys > in HashSet, member objects are used to calculate hash code values. For two objects that are the same, the equal () method is used to check whether they are equal. Returning false indicates that the two objects are different In HashMap, use key objects to calculate hash code values. > The hash mapping hash code value is calculated using the key object. Here, the member object is used to calculate the same hash code value. For two objects, the equal sign () method is used to check whether they are equal. Returning false indicates that the two objects are different

So let me end my question

>I think HashMap and HashSet calculate hash codes in the same way. Why are they different? > You can provide a specific example. How do hash sets and hash marks calculate hash codes differently? > I know what a key object is, but what does a member object mean? > HashMap can do something with HashSet and faster Why do we need HashSet? Example:

HashMap <Object1,Boolean>= new HashMap<Object1,boolean>();
map.put("obj1",true);  => exist
map.get("obj1");  =>if null = not exist,else exist

Solution

Performance:

If you look at the source code of HashSet (at least JDK 6), you use HashMap internally, so it basically conforms to what you do with the sample code

Therefore, if you need a set implementation, you can use HashSet. If you need a map – HashMap The code using HashMap instead of HashSet will have exactly the same performance as using HashSet directly

Select the correct set

Map – map keys to values (associative array) – http://en.wikipedia.org/wiki/Associative_array.

Set – a set that does not contain duplicate elements – http://en.wikipedia.org/wiki/Set_ (computer_science).

If the only thing you need is to check whether an element exists - use set Your code will be clearer and easier to understand

If you need to store some data for your elements – use maps