How Does Java's HashMap Handle Key Collisions?

Handling Collisions in Java HashMap

It is crucial to understand that Java allows objects with different values to have the same hash code. This can occur due to the nature of hash functions, which may produce the same result for distinct inputs.

Internal Mechanism of HashMap

Internally, a HashMap divides its storage into buckets based on hash codes. When encountering a key-value pair, it calculates the hash code of the key and locates the corresponding bucket. The bucket then stores the pair.

Resolving Collisions

To handle situations where multiple objects have the same hash code, HashMap employs a strategy known as chaining. When such a collision occurs, it forms a linked list within the bucket. Each list node represents a key-value pair that has the same hash code.

Retrieval and Removal

When retrieving a value from the HashMap, it follows a similar process. It calculates the hash code of the search key and retrieves the corresponding bucket. It then iterates through the linked list within the bucket, comparing each key with the search key using the equals() method.

Implications for equals() and hashCode()

To ensure the efficiency of HashMap, it is essential that the equals() and hashCode() methods of the object class have specific properties:

• If two objects are equal, they must have the same hash code. This is crucial to avoid storing equal objects in different buckets, making retrieval difficult.
• For different objects, it does not matter whether their hash codes are equal or not. HashMap will still be able to differentiate them using the equals() method within the linked list.

The above is the detailed content of How Does Java's HashMap Handle Key Collisions?. For more information, please follow other related articles on the PHP Chinese website!