Question: Can A Map Have Duplicate Values?

What happens if we put duplicate key in HashMap?

The prior value for the key is dropped and replaced with the new one.

So, the previous value gets overwritten.

Associates the specified value with the specified key in this map.

If the map previously contained a mapping for the key, the old value is replaced..

Which map can store duplicate keys?

You can use a TreeMap with a custom Comparator in order to treat each key as unequal to the others. It would also preserve the insertion order in your map, just like a LinkedHashMap. So, the net result would be like a LinkedHashMap which allows duplicate keys!

Can Java map have duplicate keys?

The map implementations provided by the Java JDK don’t allow duplicate keys. If we try to insert an entry with a key that exists, the map will simply overwrite the previous entry.

Can map contain duplicate values?

A Map cannot contain duplicate keys and each key can map to at most one value. HashMap and LinkedHashMap allow null key and null value but TreeMap doesn’t allow null key and null value.

Can Hashtable have duplicate values?

Hashtable Features It does not accept duplicate keys. It stores key-value pairs in hash table data structure which internally maintains an array of list.

Does linked list allow duplicates?

3) ArrayList and LinkedList are ordered collection e.g. they maintain insertion order of elements i.e. the first element will be added to the first position. 4) ArrayList and LinkedList also allow duplicates and null, unlike any other List implementation e.g. Vector.

Can ArrayList contain duplicates?

ArrayList allows duplicate values while HashSet doesn’t allow duplicates values. Ordering : ArrayList maintains the order of the object in which they are inserted while HashSet is an unordered collection and doesn’t maintain any order.

What happens if we trying to add duplicate values in set?

If we insert duplicate values to the Set, we don’t get any compile time or run time errors. It doesn’t add duplicate values in the set. Below is the add() method of the set interface in java collection that returns Boolean value either TRUE or FALSE when the object is already present in the set.

Can HashSet contain duplicates Java?

HashSet doesn’t allow duplicates. If you try to add a duplicate element in HashSet, the old value would be overwritten. HashSet allows null values however if you insert more than one nulls it would still return only one null value. HashSet is non-synchronized.

How do I know if a map has duplicates?

It’s quite simple , follow these steps: Create a HashMap of Integer key and value pair. Iterate through your array , and for every element in your array check whether it is present in the HashMap using ContainsKey() function. If not present , put it in the HashMap using put() function.More items…

How do you add duplicates in maps?

Map does not supports duplicate keys. you can use collection as value against same key.

Can a map have two keys with the same value?

A map will always return the Object tied to that key, the value from the entry. Map performance degrades rapidly if hashCode() returns the same (or similar) values for different keys.