Hashmap internal implementation analysis in java
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four things we should know about before going into the internals of how does HashMap work in Java -
HashMap works on the principal of hashing.
Map.Entry interface - This interface gives a map entry (key-value pair). HashMap in Java stores both key and value object, in bucket, as an object of Entry class which implements this nested interface Map.Entry.
hashCode() -HashMap provides put(key, value) for storing and get(key) method forretrieving Values from HashMap. When put() method is used to store (Key, Value) pair, HashMap implementation calls hashcode on Key object to calculate a hash that is used to find a bucket where Entry object will be stored. When get() method is used to retrieve value, again key object is used to calculate a hash which is used then to find a bucket where that particular key is stored.
equals() - equals() method is used to compare objects for equality. In case of HashMap key object is used for comparison, also using equals() method Map knows how to handlehashing collision (hashing collision means more than one key having the same hash value, thus assigned to the same bucket. In that case objects are stored in a linked list, refer figure for more clarity.
HashMap changes in Java 8
Though HashMap implementation provides constant time performance O(1) for get() and put() method but that is in the ideal case when the Hash function distributes the objects evenly among the buckets.
HashMap works on the principal of hashing.
Map.Entry interface - This interface gives a map entry (key-value pair). HashMap in Java stores both key and value object, in bucket, as an object of Entry class which implements this nested interface Map.Entry.
hashCode() -HashMap provides put(key, value) for storing and get(key) method forretrieving Values from HashMap. When put() method is used to store (Key, Value) pair, HashMap implementation calls hashcode on Key object to calculate a hash that is used to find a bucket where Entry object will be stored. When get() method is used to retrieve value, again key object is used to calculate a hash which is used then to find a bucket where that particular key is stored.
equals() - equals() method is used to compare objects for equality. In case of HashMap key object is used for comparison, also using equals() method Map knows how to handlehashing collision (hashing collision means more than one key having the same hash value, thus assigned to the same bucket. In that case objects are stored in a linked list, refer figure for more clarity.
HashMap changes in Java 8
Though HashMap implementation provides constant time performance O(1) for get() and put() method but that is in the ideal case when the Hash function distributes the objects evenly among the buckets.
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