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Java 8 – How to find an entry based on the Key in a Map or HashMap ?

February 10, 2023 SJ Collection, Java 8 0

In this article, we will discuss how to find an entry based on the Key in a HashMap using Java 8 Stream

Find an entry based on Key in a HashMap :

To find an entry based on the Key,

  • First iterate through entrySet
  • Then get the entry by comparing the Key

Here, we will discuss 2 approaches to find an entry based on the Key from HashMap

  • Using Java 8 Stream
  • Before Java 8

1. Using Java 8 Stream :

  • Iterate through entry set using Stream and filter required entry by comparing Key using Stream.filter() method
  • Now there are 2 possibilities on comparison,
    • If the entry is present with the supplied Key, then corresponding entry will be printed to the console
    • If it is not present, nothing will be printed in the console

FindEntryBasedOnKeyInMapUsingJava8Stream.java

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package in.bench.resources.find.entry.map;
 
import java.util.HashMap;
import java.util.Map;
 
public class FindEntryBasedOnKeyInMapUsingJava8Stream {
 
    public static void main(String[] args) {
 
        // 1. creating HashMap object of type <String, Integer>
        Map<String, Integer> countryPopulation = new HashMap<>();
 
 
        // 1.1 adding key-value pairs to HashMap object
        countryPopulation.put("Pakistan", 220892331);
        countryPopulation.put("Russia", 146748590);
        countryPopulation.put("Brazil", 213728559);
        countryPopulation.put("Indian", 382357386);
        countryPopulation.put("America", 332429717);
 
 
        // 1.2 print original Map entries
        System.out.println("1. Original Map Entries :- \n");
 
 
        // 1.3 print Map entries to console
        countryPopulation.forEach((key, value) -> System.out.println(
                "Key : " + key  + "\t\t"  + "Value : "  + value
                ));
 
 
 
        // 2. find Entry on the basis of Key
        String keyToFind = "Brazil";
 
 
        // 2.1 print to console
        System.out.println("\n\n2. Entry which has Key '" + keyToFind + "'\n");
 
 
        // 2.2 Iterate and find Entry based on Key
        countryPopulation
        .entrySet()
        .stream()
        .filter(entry -> entry.getKey().equals(keyToFind))
        .forEach(System.out::println);;
    }
}

Output :

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1. Original Map Entries :-
 
Key : Pakistan      Value : 220892331
Key : America       Value : 332429717
Key : Brazil        Value : 213728559
Key : Indian        Value : 382357386
Key : Russia        Value : 146748590
 
 
2. Entry which has Key 'Brazil'
 
Brazil=213728559

2. Before Java 8 :

  • Iterate through entry set using enhanced for-loop and filter required entry by comparing Key using if–condition
  • Now there are 2 possibilities on comparison,
    • If the entry is present with the supplied Key, then corresponding entry will be printed to the console
    • If it is not present, nothing will be printed in the console

FindEntryBasedOnKeyInMap.java

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package in.bench.resources.find.entry.map;
 
import java.util.HashMap;
import java.util.Map;
 
public class FindEntryBasedOnKeyInMap {
 
    public static void main(String[] args) {
 
        // 1. creating HashMap object of type <String, Integer>
        Map<String, Integer> countryPopulation = new HashMap<>();
 
 
        // 1.1 adding key-value pairs to HashMap object
        countryPopulation.put("Pakistan", 220892331);
        countryPopulation.put("Russia", 146748590);
        countryPopulation.put("Brazil", 213728559);
        countryPopulation.put("Indian", 382357386);
        countryPopulation.put("America", 332429717);
 
 
        // 1.2 print original Map entries
        System.out.println("1. Original Map Entries :- \n");
 
 
        // 1.3 print Map entries to console
        countryPopulation.forEach((key, value) -> System.out.println(
                "Key : " + key  + "\t\t"  + "Value : "  + value
                ));
 
 
 
        // 2. find Entry on the basis of Key
        String keyToFind = "Brazil";
 
 
        // 2.1 print to console
        System.out.println("\n\n2. Entry which has Key '" + keyToFind + "'\n");
 
 
        // 2.2 Iterate and find Entry based on Key
        for(Map.Entry<String, Integer> entry : countryPopulation.entrySet()) {
 
            if(entry.getKey().equals(keyToFind)) {
                System.out.println(entry);
            }
        }
    }
}

Output :

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1. Original Map Entries :-
 
Key : Pakistan      Value : 220892331
Key : America       Value : 332429717
Key : Brazil        Value : 213728559
Key : Indian        Value : 382357386
Key : Russia        Value : 146748590
 
 
2. Entry which has Key 'Brazil'
 
Brazil=213728559

Related Articles :

References :

Happy Coding !!
Happy Learning !!

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