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There are two interfaces for implementing Map in java: Map and SortedMap, and three classes: HashMap, LinkedHashMap, and TreeMap. The hierarchy of Java Map is given below: A Map doesn't allow duplicate keys, but you can have duplicate values.
- HashMap
Java HashMap. Java HashMap class implements the Map...
- HashMap
- Creating Map Objects
- Methods in Java Map Interface
- Performing Operations Using Map Interface and Hashmap Class
- FAQs in Java Map Interface
Since Map is an interface, objects cannot be created of the type map. We always need a class that extends this map in order to create an object. And also, after the introduction of Genericsin Java 1.5, it is possible to restrict the type of object that can be stored in the Map. Syntax:Defining Type-safe Map
Example: Classes that implement the Map interface are depicted in the below media and described later as follows:
Since Map is an interface, it can be used only with a class that implements this interface. Now, let’s see how to perform a few frequently used operations on a Map using the widely used HashMap class. And also, after the introduction of Genericsin Java 1.5, it is possible to restrict the type of object that can be stored in the map.
import java.util.Map; import java.util.TreeMap; class Main { public static void main(String[] args) { // Creating Map using TreeMap Map<String, Integer> values = new TreeMap<>(); // Insert elements to map values.put("Second", 2); values.put("First", 1); System.out.println("Map using TreeMap: " + values); // Replacing the values values.replace ...
The Map interface includes methods for basic operations (such as put, get, remove, containsKey, containsValue, size, and empty ), bulk operations (such as putAll and clear ), and collection views (such as keySet, entrySet, and values ). The Java platform contains three general-purpose Map implementations: HashMap, TreeMap, and LinkedHashMap.
- size. int size() Returns the number of key-value mappings in this map. If the map contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE.
- isEmpty. boolean isEmpty() Returns true if this map contains no key-value mappings. Returns: true if this map contains no key-value mappings.
- containsKey. boolean containsKey(Object key) Returns true if this map contains a mapping for the specified key. More formally, returns true if and only if this map contains a mapping for a key k such that (key==null ?
- containsValue. boolean containsValue(Object value) Returns true if this map maps one or more keys to the specified value. More formally, returns true if and only if this map contains at least one mapping to a value v such that (value==null ?
Feb 1, 2020 · That's where the java.util.Map interface shows up. A Map associates items to keys, allowing us to retrieve items by those keys. Such associations carry much more sense than associating an index to an item. Map is a generic interface with two types, one for the keys and one for the values.
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Nov 8, 2022 · The Java platform contains three purpose Map interface implementations: HashMap, TreeMap, and LinkedHashMap. Their behavior and performance are precisely analogous to HashSet, TreeSet, and...
