Hashmap put example with duplicate key

Опубликовано: 01 Июнь 2025
на канале: CodeWrite

Download 1M+ code from https://codegive.com/4ed43e0
deep dive into hashmap's `put` method with duplicate keys

this tutorial provides a comprehensive explanation of the `put` method in java's `hashmap`, with a particular focus on how it handles duplicate keys. we'll cover the underlying mechanisms, the implications for performance, and provide detailed code examples.

*1. what is a hashmap?*

a `hashmap` in java is an implementation of the `map` interface. it stores data in key-value pairs. crucially, it's based on the concept of *hashing*, which allows for very fast retrieval of values given their corresponding keys.

*key characteristics:*

*unordered:* the order in which you insert elements isn't guaranteed to be preserved. prior to java 1.8, the insertion order was not maintained. from java 1.8 onwards, the `hashmap` internally keeps track of insertion order (for iteration purposes). however, it's still not guaranteed unless you explicitly use a `linkedhashmap`.
*allows `null` keys and `null` values (up to java 7).* from java 8 onwards, only one `null` key is allowed (the first one) . multiple `null` values are permitted.
*not synchronized:* `hashmap` is not thread-safe. if multiple threads access and modify a `hashmap` concurrently, you need external synchronization or use a thread-safe alternative like `concurrenthashmap`.
*hash table implementation:* it uses a hash table to store the key-value pairs. the keys are hashed to determine the index (bucket) in the hash table where the corresponding value is stored.

*2. the `put` method: adding or replacing key-value pairs*

the `put(k key, v value)` method is the core function for adding or updating entries in a `hashmap`. here's a breakdown of what happens under the hood:

*steps involved in `put(key, value)`:*

1. *null key check:* if the key is `null`, the value is stored in the bucket at index 0. before java 8, this was the only way `null` keys could be handled. from java 8 onwards, it ensures that only one `null` ...

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