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Remove an Entry using value from HashMap while Iterating over it

  • Last Updated : 11 Dec, 2018

Given a HashMap and a value in Java, the task is to remove an entry from this HashMap using the value, while iterating over it.

Examples:

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Input: HashMap: {1=Geeks, 2=ForGeeks, 3=GeeksForGeeks}, value = “ForGeeks”
Output: {1=Geeks, 3=GeeksForGeeks}

Input: HashMap: {1=G, 2=e, 3=e, 4=k, 5=s}, value = k
Output: {1=G, 2=e, 3=e, 5=s}



  • Using Java 7 and before:
    1. Get the HashMap and the Value
    2. Create an iterator to iterate over the HashMap using HashMap.iterate() method.
    3. Iterate over the HashMap using the Iterator.hasNext() method.
    4. While iterating, check for the value at that iteration to be equal to the value specified. The entry value of the Map can be obtained with the help of entry.getValue() method.
    5. If the value matches, remove the entry of that iteration from the HashMap using remove() method.
    6. The required entry has been successfully removed.

    Syntax:

    Iterator> 
        iterator = map.entrySet().iterator();
    
    while (iterator.hasNext()) {
        Map.Entry entry = iterator.next();
        if (valueToBeRemoved.equals(entry.getValue())) {
            iterator.remove();
        }
    }
    

    Below is the implementation of the above approach:




    // Java program to remove an entry using value
    // from a HashMap while iterating over it
      
    import java.util.*;
      
    public class GFG {
        public static void main(String[] args)
        {
      
            // Create a HashMap
            HashMap<Integer, String>
                map = new HashMap<>();
      
            // Populate the HashMap
            map.put(1, "Geeks");
            map.put(2, "ForGeeks");
            map.put(3, "GeeksForGeeks");
      
            // Get the value to be removed
            String valueToBeRemoved = "ForGeeks";
      
            // Print the initial HashMap
            System.out.println("Original HashMap: "
                               + map);
      
            // Get the iterator over the HashMap
            Iterator<Map.Entry<Integer, String> >
                iterator = map.entrySet().iterator();
      
            // Iterate over the HashMap
            while (iterator.hasNext()) {
      
                // Get the entry at this iteration
                Map.Entry<Integer, String>
                    entry
                    = iterator.next();
      
                // Check if this value is the required value
                if (valueToBeRemoved.equals(entry.getValue())) {
      
                    // Remove this entry from HashMap
                    iterator.remove();
                }
            }
      
            // Print the modified HashMap
            System.out.println("Modified HashMap: "
                               + map);
        }
    }
    Output:
    Original HashMap: {1=Geeks, 2=ForGeeks, 3=GeeksForGeeks}
    Modified HashMap: {1=Geeks, 3=GeeksForGeeks}
    
  • Using Java 8 lambda expressions:
    1. Get the HashMap and the Value
    2. Get the entry set of this map using HashMap.entrySet() method.
    3. Using lambda expression, remove the entry from the map if the value is equal to the value specified. The entry value of the Map can be obtained with the help of entry.getValue() method.
    4. The required entry has been successfully removed.

    Syntax:

    map.entrySet()
       .removeIf(
           entry -> (valueToBeRemoved
                        .equals(entry.getValue())));
    

    Below is the implementation of the above approach:




    // Java program to remove an entry using value
    // from a HashMap while iterating over it
      
    import java.util.*;
      
    public class GFG {
        public static void main(String[] args)
        {
      
            // Create a HashMap
            HashMap<Integer, String>
                map = new HashMap<>();
      
            // Populate the HashMap
            map.put(1, "Geeks");
            map.put(2, "ForGeeks");
            map.put(3, "GeeksForGeeks");
      
            // Get the value to be removed
            String valueToBeRemoved = "ForGeeks";
      
            // Print the initial HashMap
            System.out.println("Original HashMap: "
                               + map);
      
            // Remove the specified entry from the Map
            map.entrySet()
                .removeIf(
                    entry -> (valueToBeRemoved.equals(entry.getValue())));
      
            // Print the modified HashMap
            System.out.println("Modified HashMap: "
                               + map);
        }
    }
    Output:
    Original HashMap: {1=Geeks, 2=ForGeeks, 3=GeeksForGeeks}
    Modified HashMap: {1=Geeks, 3=GeeksForGeeks}
    



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