Java Implant: Java Map Interface

Map

Map is a collection of key value pair.
By default, a map has 16 buckets
After threshold value default of which is 12, the size of map automatically increases
Using hash function We can get the corresponding bucket hash where the data is to be stored.
If we add null key, then data will go in the first bucket.
In Java 8 hash map replaces linked list with a binary tree When the number of elements in a bucket, reach certain threshold.

While converting the list to binary tree, hash code is used as a branching variable. If there are two different hash codes In the same bucket, one is considered bigger and goes to left of tree and Other goes to right of tree.

Types of Maps

Introduced in Java 1.5.
Thread, safe, multiple threads are allowed to operate.
One thread can lock a bucket or segment at a time.
Fast performance
Null key and values are not allowed.
Locking is done at segment level instead of locking entire object.
Iterator is fail safe, If we try to read while changing the structure of object, it does not throw any exception.
It is used in multi threaded environment.
We will get thread safety without locking the total map object. Just do a bucket level lock.
At a time, multiple threads are allowed to operate on map objects safely.
Read operation can be performed without lock, but write operation can be performed with bucket level lock.
While one thread is reading map objects, the other thread is allowed to modify the map and we won’t get concurrent modification exception.
Iterator of concurrent hash map is fail safe And won’t raise Concurrent modification exception.

Each bucket is a link list of nodes Which contains a key, value, hash And next variable.

If key is null, entry is placed in the zero bucket.
We calculate the hash key using mod of Number of buckets and ID. Based on which we assign the value to a hash bucket.
If there is collision that is hash key of two entries Is same, we add the new entry as next node To current node In hash key or bucket.
In Java 8 Under certain conditions, link list is converted to balanced tree

For example, a bucket contains five nodes And then there is a hashing collision on the linked list of that bucket, then it will turn in Balance tree.

Thread safe Only one thread is allowed at a time.
Slow performance
Null key and values are not allowed.
Iterator is fail first If we modify while it throws concurrent modification exception.
We will get thread safety by locking the whole map object.
At a time, one thread is allowed to operate on a map object.
Every read and write operations required, total map object
While one thread is iterating map object, the other threads are not allowed to modify the map. Otherwise, we will get concurrent modification exception.
Iterator of hash table is fail fast, and it will raise concurrent modification exception.
Null is not allowed for both keys and values.
Introduced in Java 1.0 version.
Insertion order is not maintained.

Thread safe and synchronised I.e. Only one thread can operate at a time.
Slow in performance
Null key And multiple null values are allowed.
We use Collections. SynchroniseMap() to synchronise.
We will get thread safety by locking the whole map object.
Works with multiple threads but At a time, only one thread is allowed to perform any operation on map object.
Every we and wide operation operations required total map object
While one thread is it map object, the other threads are not allowed to modify the map. Otherwise, we will get concurrent modification exception.
Iterator of synchronised map is fail fast and it will raise concurrent modification exception.
Null is allowed for both keys and values
Introduced in Java 1.2 version

Java Implant