What are the real time problems with HashMap?

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What are the real time problems with HashMap?

Java HashMap cannot have duplicate keys but it can have duplicates as values. Hash Map can have only one NULL key and multiple NULL Values. The Order in which, We add the values to HashMap is not guaranteed, hence the Insertion order is not Preserved. Searching the Object is fast since the Java HashMap has the Keys.

What are the disadvantages of HashMap?

Disadvantages of HashMap

  • Potential of collision when 2 distinct keys generate the same hashCode() value worse the performance of the hashMap.
  • Occasionally HashMaprequires resizing when the original size of HashMap buckets are full.

When should we use HashMap in Java?

Using HashMap makes sense only when unique keys are available for the data we want to store. We should use it when searching for items based on a key and quick access time is an important requirement. We should avoid using HashMap when it is important to maintain the same order of items in a collection.

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Should I use HashMap or Hashtable?

HashMap should be preferred over Hashtable for the non-threaded applications. In simple words , use HashMap in unsynchronized or single threaded applications . We should avoid using Hashtable, as the class is now obsolete in latest Jdk 1.8 . Oracle has provided a better replacement of Hashtable named ConcurrentHashMap.

Can HashMap have duplicate keys?

Duplicates: HashSet doesn’t allow duplicate values. HashMap stores key, value pairs and it does not allow duplicate keys.

Which is correct with respect to HashMap?

Explanation: The key is hashed twice; first by hashCode() of Object class and then by internal hashing method of HashMap class. Explanation: Hashmap outputs in the order of hashcode of the keys. So it is unordered but will always have same result for same set of keys.

What is one main disadvantage of an ArrayList?

A possible disadvantage of ArrayList is that it holds only object types and not primitive types (eg, int ). To use a primitive type in an ArrayList, put it inside an object or use of the wrapper classes (eg, Integer, Double, Character.).

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What is a hash set in Java?

HashSet is a data type in Java that is used to create a mathematical set. HashSet is part of the Java Collections framework and allows you to store data using the hash table data type.

Which collection is best for searching in Java?

3 Answers. If you are searching a collection by key, you should generally use a HashMap, which finds items in the map based on their key in expected O(1) time.

Why HashMap is not thread-safe in Java?

We can see that it prints the keys which are not in map, even though we have put the same key in map before doing get operation. Its strange to see the values printed, that’s why hashmap is not thread safe implementation working in concurrent environment.

When should I use Hashtable?

Mainly when:

  1. The input can’t be hashed (e.g. you’re given binary blobs and don’t know which bits in there are significant, but you do have an int cmp(const T&, const T&) function you could use for a std::map ), or.
  2. the available/possible hash functions are very collision prone, or.
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Can we store objects in HashMap?

Internal working. All instances of Entry class are stored in an array declard as ‘transient Entry[] table’ . For each key-value to be stored in HashMap, a hash value is calculated using the key’s hash code. This hash value is used to calculate the index in the array for storing Entry object.