What is a Map in Java? Everything you need to know

Java has an implementation of the map interface. The java.util package is a key-value pair that may be used to store and retrieve data. In the Collection interface, Map is not a subclass. Due to its unique characteristics, it is distinct from the other collection kinds. Each key on a map is different.

Why and when should utilise Maps as a brainstorming tool?

Using dictionaries as an example, maps are ideal for use in key-value association mapping. Key lookups and element retrieval and updating are both possible with the maps. Following are a few examples of typical scenarios:

  • Error codes and their meanings are laid forth on a visual map.
  • Zipcodes and cities are shown on a map.
  • Managers and employees are depicted on a map Managers are assigned a value (key) for the number of employees they supervise.
  • Students and classes are depicted on this map. There is a list of students linked with each class (key) (value).

Because Map is an interface, no new objects of type map may be created. To build an object, we must always extend this map with a new class. Object types may now be restricted in the Map thanks to Generics, which were introduced in Java 1.5.

The syntax for Defining Type-safe Map

Map hm = new HashMap(); 
// Obj is the type of the object to be stored in Map

Map User Interface Characteristics

  • Each key in a Map can only map to one value, hence multiple keys are impossible in a Map. The HashMap and LinkedHashMap, for example, support null keys and null values, whereas the TreeMap does not.
  • The order of a map is determined by the implementations that are being used. TreeMap and LinkedHashMap, on the other hand, have orders that can be predicted, but HashMap does not.
  • The two interfaces for implementing Map in Java are Map and Sorted Map. LinkedHashMap, TreeMap, and LinkedHashMap are all classes of Maps.

Methods in Map Interface

clear()

Using this technique, you may clean and remove all of the items or mappings from a Map collection.

containsKey(Object)

Using this technique, you may determine whether or not a certain key has been mapped to the Map. When passed the key element, it checks to see if it is mapped in the map and returns True if it is.

containsValue(Object)

Using this function, you may determine if a given value is being mapped to a single key in the Map or whether it is shared by several keys. Value is passed as an argument, and if any of the map’s keys correspond to it, then this function returns True.

entrySet()

Using the map’s elements, this technique may be used to generate a new set. If we want to save the map components in a new set, then we may use this method.

equals(Object)

Maps may be checked for equality using this approach. If a map is supplied as a parameter, it checks to see if the elements in that map are equal to those in this map.

get(Object)

The value assigned to a certain key in the parameter may be retrieved using this technique. When there is no such mapping for the key in the map, it returns NULL.

hashCode()

You may use this function to construct a hashCode from a key-value map that you’ve provided.

isEmpty()

Using this technique, you can determine whether or not a map has any entries for key-value pairs. True if there is no mapping available.

keySet()

Using this approach, you may get a Set view of the keys in this map. Whenever a modification is made to the map, it is immediately reflected in the set.

put(Object, Object)

In this map, the supplied value is associated with the specified key using this technique.

putAll(Map)

Copy all mappings from one map to another using this technique.

remove(Object)

Using this technique, you can delete a key’s mapping from this map if it exists.

size()

It is possible to get the total number of key/value pairs in the map using this approach.

values()

Use this method to build a collection from the map’s data. A Collection view of the HashMap’s values is returned by this method.

getOrDefault(Object key, V defaultValue)

DefaultValue if this map does not have a mapping for the key or the value of the supplied key.

merge(K key, V value, BiFunction<? super V,? super V,? extends V> remappingFunction)

Assigns the provided non-null value to the specified key if it is not already associated with a value or is associated with null.

putIfAbsent(K key, V value)

For example, it returns null if the supplied key does not already have a value assigned to it (or if it is mapped to a value that is not null).

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Ratnesh
Ratneshhttps://www.networkherald.com
Founder and Chief Editor of Network Herald. A passionate Blogger, Content Writer from Mumbai. Loves to cover every current affair in terms of technology. He writes about the how-to guides, tips and tricks, top list articles.

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