![]() What is the requirement for an object to be used as a key or value in HashMap? ( answer) If a collision occurs, then the entry object which contains both key and value is added to a linked list, and that linked list is stored into the bucket location.Ģ. The hashcode() method is used in conjunction with a hash function to find the correct location for the object into the bucket. It is responsible for storing an object into the backend array. The put() method of HashMap works in the principle of hashing. How does the put() method of HashMap works in Java? ( answer) This list includes questions based on the internal implementation of HashMap, the Map API, how you use HashMap, and standard best practices while using HashMap in a Java application.ġ. Here is my list of HashMap questions from Java Interviews. That will not only help you to do well on interviews but also help you to understand the fundamentals better. Similarly, if you need a hash table implementation that is thread-safe and can be used in a concurrent application without compromising the Scalability, then consider using a ConcurrentHashMapfrom JDK 5.ītw, if you are new to the Java world and JDK API in particular, I suggest you first go through an online Java course like the ones I have recommended in my list of best free core Java courses. If you wish to keep mappings sorted, then you can use TreeMap, which is a sorted map implementation. For example, if you want to preserve the order of mapping, then you can consider using LinkedHashMap. Though, if you have a special need, you can use other hash table implementations available in JDK. In Java, several implementations of hash table data structures exist like Hashtable, ConcurrentHashMap, LinkedHashMap, etc. The hash table data structure allows you to search for a value in O(1) time if you have a key. It is an implementation of hash table data structure, and it's not a surprise that HashMap is so useful, as someone has rightly said, "if you could have just one data structure, make it a hash table". There is hardly a real-world Java project, where I haven't seen the use of HashMap. Along with ArrayList, it is one of the most used classes from Java's collection framework. A Naive hashCode() ImplementationĪ naive hashCode() implementation that fully adheres to the above contract is actually quite straightforward.The is one of the workhorses of JDK. (This is typically implemented by converting the internal address of the object into an integer, but this implementation technique is not required by the JavaTM programming language.)” 4. ![]() “As much as is reasonably practical, the hashCode() method defined by class Object does return distinct integers for distinct objects. However, developers should be aware that producing distinct integer results for unequal objects improves the performance of hash tables. If two objects are unequal according to the equals() method, calling the hashCode method on each of the two objects doesn’t need to produce distinct integer results. ![]()
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