How HashMap Works Internally in Java
Understanding the Internal Mechanism of HashMap in Java
How HashMap Works Internally in Java
HashMap in Java stores key-value pairs in an array and uses a hash function to determine the index for each key, enabling fast retrieval and insertion operations. This makes HashMap a useful data structure for storing and accessing data efficiently, especially in cases where quick lookups are required. By using key-value pairs and hashing techniques, HashMap provides a way to store and retrieve data based on keys, offering better performance than other data structures like arrays or linked lists.
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1 - HashMap in Java is a data structure that allows storing key value pairs and provides fast retrieval of values based on keys.
2) When you put a key value pair into a HashMap, Java uses the key's hash code to determine the index where the value will be stored in an array.
3) If two keys have the same hash code (known as a “hash collision”), Java uses a linked list or a balanced tree to store these key value pairs.
4) HashMap uses an array to store the key value pairs, and each element in the array is known as a “bucket.” The number of buckets in a HashMap is called the “capacity.”
5) When a HashMap is created, its initial capacity is set to a default value, but it can be increased or decreased as needed based on factors like load factor and number of elements.
6) The load factor is a measure of how full the HashMap is allowed to get before its capacity is automatically increased. It helps in balancing between time and space trade offs.
7) When you retrieve a value from a HashMap using a key, Java calculates the hash code of the key, uses it to find the corresponding bucket, and then searches for the value within that bucket.
8) HashMap provides constant time performance for basic operations like get and put on average, but in the worst case (due to hash collisions), these operations can degrade to O(n).
9) In Java 8 and later versions, if a bucket's size grows beyond a certain threshold, the bucket is converted from a linked list to a balanced tree for performance optimization.
10) HashMap in Java is not synchronized, meaning that it is not thread safe. If multiple threads access a HashMap concurrently and at least one of the threads modifies the map structurally, it must be synchronized externally.
11) To make a HashMap thread safe, you can use the ConcurrentHashMap class, which provides thread safe property without the need for external synchronization, making it efficient for concurrent operations.
12) The HashMap class in Java provides various methods for manipulating and iterating over the key value pairs, such as put, get, remove, keySet, values, entrySet, and more.
13) When iterating over a HashMap, the order of the key value pairs is not guaranteed, as it depends on the hash codes and buckets used for storage.
14) HashMap allows null keys and values, meaning you can store null values in a HashMap and retrieve them based on null keys.
15) Understanding the internal working of HashMap and its performance characteristics is crucial for writing efficient code and designing applications that depend heavily on key value pair storage and retrieval.
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