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What is the LinkedHashMap.entrySet method in Java?

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Grokking Modern System Design Interview for Engineers & Managers

Ace your System Design Interview and take your career to the next level. Learn to handle the design of applications like Netflix, Quora, Facebook, Uber, and many more in a 45-min interview. Learn the RESHADED framework for architecting web-scale applications by determining requirements, constraints, and assumptions before diving into a step-by-step design process.

A LinkedHashMap is the same as a regular HashMap, except that a LinkedHashMap maintains the insertion order, whereas a HashMap does not.

Internally, the LinkedHashMap uses a doubly-linked list to maintain the insertion order.

The entrySet method

In a LinkedHashMap, we can use the entrySet method to get all the entrieskey-value mappings of the LinkedHashMap object as a set view.

Syntax

public Set<Map.Entry<K,V>> entrySet()

Parameters

This method doesn’t take any parameters.

Return value

The entrySet method returns a set view of all of the entries in the map.

Code

The example below shows how to use the entrySet method.

import java.util.LinkedHashMap;
import java.util.Set;
import java.util.Map;
class EntrySetExample {
public static void main( String args[] ) {
LinkedHashMap<Integer, String> map = new LinkedHashMap<>();
map.put(1, "one");
map.put(2, "two");
System.out.println("The map is -" + map );
Set<Map.Entry<Integer, String>> entries = map.entrySet();
System.out.println("The entries are -" + entries);
System.out.println("\nAdding a new entry 4 - four to the map" );
map.put(4, "four");
System.out.println("After adding the entries are -" + entries);
}
}

Explanation

In the code above:

  • In line 1, we import the LinkedHashMap class.

  • In line 7, we create a LinkedHashMap object with the name map.

  • In lines 8 and 9, we use the put method to add two mappings ({1=one, 2=two}) to the map object.

  • In line 13, we get the entries of the LinkedHashMap with the entrySet method and store them in the entries variable.

  • In line 17, we add a new entry 4 - "four" to the map.

  • In line 19, we print entries. The newly added entry, 4 - "four", will automatically be available in the entries variable without the need to call the entrySet method because the entrySet method returns the set view.

RELATED TAGS

java
communitycreator

Grokking Modern System Design Interview for Engineers & Managers

Ace your System Design Interview and take your career to the next level. Learn to handle the design of applications like Netflix, Quora, Facebook, Uber, and many more in a 45-min interview. Learn the RESHADED framework for architecting web-scale applications by determining requirements, constraints, and assumptions before diving into a step-by-step design process.

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