What can we use instead of HashMap in Java?

4 Answers. I doubt it’s the hashmap that is causing you problems, but the ArrayList, since it allocates room for 10 entries by default. If you’re only storing one or two values for each index, then that will be wasteful. You could try setting the initial size to 1 or 2 to see if that helps.

When would you want to use a Map vs a HashMap in Java?

The Map is an interface in Java used to map the key-pair values. It is used to insert, update, remove the elements. Whereas the HashMap is a class of Java collection framework. The Map interface can only be used with an implementing class.

When would you use Linkedhash Map and TreeMap?

That is, if you need to get the keys back in insertion order, then use LinkedHashMap. If you need to get the keys back in their true/natural order, then use TreeMap.

When would you not use a HashMap?

1 Answer. If all of your object keys have the same hashCode , or you don’t even have some kind of key, or you have null keys, or your algorithm or program doesn’t require a hashmap.

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.

What is the difference between HashMap and Map in Java?

Map is an interface, HashMap is a class that implements Map . Map is an interface; HashMap is a particular implementation of that interface. HashMap uses a collection of hashed key values to do its lookup. TreeMap will use a red-black tree as its underlying data store.

What is the difference between Map and HashMap in Scala?

Map is the interface for immutable maps while scala. collection. HashMap is a concrete implementation. HashMap doesn’t allow duplicate keys but allows duplicate values.

What is the difference between HashMap and TreeMap in Java with example?

HashMap implements Map, Cloneable, and Serializable interface. TreeMap implements NavigableMap, Cloneable, and Serializable interface. HashMap allows a single null key and multiple null values. TreeMap does not allow null keys but can have multiple null values.

What is the difference between HashMap and LinkedHashMap in Java?

The Major Difference between the HashMap and LinkedHashMap is the ordering of the elements. The LinkedHashMap provides a way to order and trace the elements. The HashMap extends AbstractMap class and implements Map interface, whereas the LinkedHashMap extends HashMap class and implements Map interface.

Why do we need HashMap in Java?

What is a HashMap useful for?

Hashmaps are probably the most commonly used implementation of the concept of a map. They allow arbitrary objects to be associated with other arbitrary objects. This can be very useful for doing things like grouping or joining data together by some common attribute.

What is the difference between map and HashMap in Java?

Maps are used for when you want to associate a key with a value and Lists are an ordered collection. Map is an interface in the Java Collection Framework and a HashMap is one implementation of the Map interface. HashMap are efficient for locating a value based on a key and inserting and deleting values based on a key.

What are the applications of HashMap?

Applications of HashMap: HashMap is mainly the implementation of hashing. It is useful when we need efficient implementation of search, insert and delete operations. Please refer to the applications of hashing for details. K – The type of the keys in the map.

What are K and V in HashMap in Java?

HashMap is a part of java.util package. HashMap extends an abstract class AbstractMap which also provides an incomplete implementation of Map interface. It also implements Cloneable and Serializable interface. K and V in the above definition represent Key and Value respectively. HashMap doesn’t allow duplicate keys but allows duplicate values.

What is the difference between list and map in Java?

Lists and Maps are different data structures. Maps are used for when you want to associate a key with a value and Lists are an ordered collection. Map is an interface in the Java Collection Framework and a HashMap is one implementation of the Map interface.