Why is hashmap fast

Never miss out on future posts by subscribing JavaHungry. Java Hungry. Java developers tutorials and coding. Difference between HashMap and Hashtable is one of the most popular java interview questions. Linux64, kernel 4. Transparent huge pages turned on. R eference CH aining hashtable a. HashMap as baseline.

I nline types CH aining, corelibs. XHashMap class. I nline types O pen A ddressing implementation, corelibs. HashMap class. R eference O pen A ddressing implementation, obtained from corelibs. Several other inline types chaining implementation were checked. Iteration seems quite simple: any inline based implementation is faster than reference based implementations speedup range from 1.

Map is growing from empty map created by default constructor to requested size. Map created with capacity enough to hold all keys, thus resize operation is excluded. It was found that any HashMap behavior highly depends on load factor. Typical scenario - actual load factors are in range 0. JavaProphet JavaProphet 14 14 silver badges 29 29 bronze badges. Hashmaps use the hashcode of the key to access directly the bucket where the entry is stored.

This is an O 1 access. If more than one element is in that bucket because of the same or similar hashcode, then you have a few more checks, but it's still way faster than iterating through a list and searching for an element.

Also: javacodegeeks. Because not the hashcode itself is used as the array index. The array which is inside the hashmap is a lot smaller depending how you initialize it and how many elements it has and the hashmap makes another calculation to calculate the real array index from the hashcode. An int is hardly a large number these days I'm sorry, but this question shows a distinct lack of research. There will be literally hundreds of websites out there that explain the basic principles of hash tables.

Show 3 more comments. Active Oldest Votes. Improve this answer. TreeMap Features Duplicate keys are not possible. It stores the keys in sorted order natural order or by a Comparator provided at map creation time. Why null key is allowed in HashMap? For HashMap, it allows one null key and there is a null check for keys, if the key is null then that element will be stored in a zero location in Entry array.

We cannot have more than one Null key in HashMap because Keys are unique therefor only one Null key and many Null values are allowed. Why is HashMap faster? HashMap is faster than HashSet because the values are associated to a unique key. In HashMap , the hashcode value is calculated using the key object. The HashMap hashcode value is calculated using the key object.

What is a HashMap used for? This class makes no guarantees as to the order of the map. It is similar to the Hashtable class except that it is unsynchronized and permits nulls null values and null key. How does a TreeMap work? TreeMap in Java. Also, all its elements store in the TreeMap are sorted by key.