Java Question
Internal working of hash map in Java

Question

Java Question

Internal working of hash map in Java

Accepted Answer

Index Calculation in Hashmap :
Hash code of key may be large enough to create an array. hash code generated may be in the range of integer and if we create arrays for such a range, then it will easily cause outOfMemoryException. So we generate index to minimize the size of array. Basically following operation is performed to calculate index :
index = hashCode(key) & (n-1).
where n is number of buckets or the size of array.

hashCode() method
hashCode() method is used to get the hash Code of an object. hashCode() method of object class returns the memory reference of object in integer form. Definition of hashCode() method is public native hashCode(). It indicates the implementation of hashCode() is native because there is not any direct method in java to fetch the reference of object. It is possible to provide your own implementation of hashCode().
In HashMap, hashCode() is used to calculate the bucket and therefore calculate the index.

equals() method
equals method is used to check that 2 objects are equal or not. This method is provided by Object class. You can override this in your class to provide your own implementation.
HashMap uses equals() to compare the key whether they are equal or not. If equals() method return true, they are equal otherwise not equal.

Top Morgan Stanley Java Developer interview questions & answers

Popular interview questions of Java Developer