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javahashmapcontainskeyobject-comparison
Mohasin Ali
Mohasin Ali

Reputation: 4015

Internal working of Java Map.containsKey() method

I am using a Map<Map, Boolean> in java and when I am trying to validate the Map with containsKey() method, it is returning always false, the inner Map always updates its keys & values. Here is the code which looks like similar to this

import java.util.HashMap;
import java.util.Map;
import java.util.Random;

public class ExampleMap
{
    private static Map<Map<Long,Boolean>, Boolean> objectDetailsToSize= new HashMap<>();
    public static void main(String[] args) 
    {
        Random rn = new Random();
        int size = 10;
        Map<Long,Boolean> detailsMap = new HashMap<>();
        for(int i=0; i< size; i++)
        {
            detailsMap.put(rn.nextLong(),rn.nextBoolean());
            if(!objectDetailsToSize.containsKey(detailsMap))
            {
                    objectDetailsToSize.put(detailsMap, rn.nextBoolean());
                    System.out.println("Why containsKey() method is failing here");
            }
        }
        
    }
}

Why Map's containsKey() method is always failing here?

Upvotes: 0

Views: 64

Answers (1)

Louis Wasserman
Louis Wasserman

Reputation: 198023

You must make a new detailsMap -- or copy your existing one -- every time through the loop. Right now, you're modifying the map that you've already put in.

Upvotes: 0

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