- Where is HashMap used in real time?
- What is the advantage of using HashMap?
- Is HashMap fast?
- Can map have duplicate keys C++?
- Why is HashMap faster?
- Is HashMap thread safe?
- Can HashMap have duplicate keys?
- Does HashMap keep order?
- What is the difference between HashMap and TreeMap?
- Can TreeMap have duplicate keys?
- When should I use HashMap?
- Does ArrayList guarantee order?
- Can we sort HashMap in Java?
- Does TreeMap allow null key?
- Does HashMap have order?
- Which map is faster in Java?
- Which is faster ArrayList or HashMap?
- Which is better HashMap or Hashtable?
- What are the real time problems with HashMap?
- Can ArrayList have duplicates?
- Does TreeMap use hashCode?
Where is HashMap used in real time?
Originally Answered: Where we use hashmap in Java in real life.
Wherever you are putting a list of objects in an array or list and then retrieving the value based on some attributes of an object, you can use hashmap.
This is used extensively as in-memory cache for static/near static values..
What is the advantage of using HashMap?
Advantages of HashMap Allows insertion of key value pair. HashMap is non synchronized. HashMap cannot be shared between multiple threads without proper synchronization. HashMap is a fail-fast iterator.
Is HashMap fast?
HashMap, being a hashtable-based implementation, internally uses an array-based data structure to organize its elements according to the hash function. HashMap provides expected constant-time performance O(1) for most operations like add(), remove() and contains(). Therefore, it’s significantly faster than a TreeMap.
Can map have duplicate keys C++?
STL map does not allow same Keys to be used. You may want to go for multi-map for that. a map will not throw any compile/run time error while inserting value using duplicate key. but while inserting, using the duplicate key it will not insert a new value, it will return the same exiting value only.
Why is HashMap faster?
HashMap is faster than HashSet because the values are associated to a unique key. … The HashMap hashcode value is calculated using the key object. Here, the member object is used to calculate the hashcode, which can be the same for two objects, so equals() method is used to check for equality.
Is HashMap thread safe?
HashMap is non synchronized. It is not-thread safe and can’t be shared between many threads without proper synchronization code whereas Hashtable is synchronized. … HashMap allows one null key and multiple null values whereas Hashtable doesn’t allow any null key or value.
Can HashMap have duplicate keys?
HashMap does not allow duplicate keys however it allows to have duplicate values. HashSet permits to have a single null value. HashMap permits single null key and any number of null values.
Does HashMap keep order?
The HashMap class does not maintain the order of the elements. This means that It might not return the elements in the same order they were inserted into it. If the application needs the elements to be returned in the same order they were inserted, LinkedHashMap should be used.
What is the difference between HashMap and TreeMap?
HashMap allows a single null key and multiple null values. TreeMap does not allow null keys but can have multiple null values. HashMap allows heterogeneous elements because it does not perform sorting on keys. TreeMap allows homogeneous values as a key because of sorting.
Can TreeMap have duplicate keys?
A TreeMap cannot contain duplicate keys. TreeMap cannot contain the null key. However, It can have null values.
When should I use HashMap?
HashMap are efficient for locating a value based on a key and inserting and deleting values based on a key. The entries of a HashMap are not ordered. ArrayList and LinkedList are an implementation of the List interface.
Does ArrayList guarantee order?
Yes. ArrayList is a sequential list. So, insertion and retrieval order is the same. If you add elements during retrieval, the order will not remain the same.
Can we sort HashMap in Java?
HashMap is not meant to keep entries in sorted order, but if you have to sort HashMap based upon keys or values, you can do that in Java. Sorting HashMap on keys is quite easy, all you need to do is to create a TreeMap by copying entries from HashMap. … This is similar of how you sort an ArrayList in Java.
Does TreeMap allow null key?
A TreeMap contains values based on the key. It implements the NavigableMap interface and extends AbstractMap class. … It cannot have null key but can have multiple null values. It is same as HashMap instead maintains ascending order(Sorted using the natural order of its key).
Does HashMap have order?
HashMap is implemented as a hash table, and there is no ordering on keys or values. TreeMap is implemented based on red-black tree structure, and it is ordered by the key. LinkedHashMap preserves the insertion order. Hashtable is synchronized in contrast to HashMap .
Which map is faster in Java?
HashMapHashMap will generally be fastest, since it has the best cache behavior ( HashMap iterates directly over the backing array, whereas TreeMap and LinkedHashMap iterate over linked data structures).
Which is faster ArrayList or HashMap?
The ArrayList has O(n) performance for every search, so for n searches its performance is O(n^2). The HashMap has O(1) performance for every search (on average), so for n searches its performance will be O(n). While the HashMap will be slower at first and take more memory, it will be faster for large values of n.
Which is better HashMap or Hashtable?
Hashtable is synchronized, whereas HashMap is not. This makes HashMap better for non-threaded applications, as unsynchronized Objects typically perform better than synchronized ones. Hashtable does not allow null keys or values. HashMap allows one null key and any number of null values.
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.
Can ArrayList have duplicates?
4) Duplicates: ArrayList allows duplicate elements but HashMap doesn’t allow duplicate keys (It does allow duplicate values). 5) Nulls: ArrayList can have any number of null elements.
Does TreeMap use hashCode?
An interesting corollary from the above analysis is that TreeMap does not use hashCode() or equals() at all! It solely relies on the compareTo() method and if your equals() does not comply with compareTo(), TreeMap does not care.