Java HashMap – How to Get Key from Value

    RahulBy 2 Mins ReadUpdated:

    Write a Java program to get keys from the hashmap using the value.

    The HashMap class is available under the java.util package. It is pretty similar to HashTable, but the HashMap is unsynchronized and also allows to stole one null key.

    In this tutorial, you will learn Java examples to get keys from a HashMap based on a defined value.

    Get Key for a Value in HashMap

    The Entry interface provides a number of methods to access key values from a HashMap. The Entry.getValue() method returns the value based on the provided key.

    Here is an example Java program to initialize a HashMap and then iterate through all key-pair using for loop.

    Let’s create a file HashMapExample1.java in your system and add the below content.

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    import java.util.HashMap;
    import java.util.Map.Entry;
     
    class HashMapExample1 {
      public static void main(String[] args) {
     
        // Define a hashmap
        HashMap<Integer, String> cities = new HashMap<>();
     
        // Adding key pair to hashmap  
        cities.put(101, "Delhi");
        cities.put(102, "New York");
        cities.put(103, "Peris");
        cities.put(104, "Denmark");
     
        // Define value to search key for
        String value = "Peris";
     
        // Iterate through hashmap using for loop
        for(Entry<Integer, String> entry: cities.entrySet()) {
          if(entry.getValue() == value) {
            System.out.println("The Key for '" + value + "' is " + entry.getKey());
            break;
          }
        }
      }
    }

    Save the file and close it.

    Now, compile the Java program and run. You will see the results below.

    Output:
    
The Key for 'Peris' is 103

    Get All Key Values in HashMap

    Here is another example showing to get all key values from a Java HashMap.

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    import java.util.HashMap;
     
    class HashmapExample2 {
      public static void main(String[] args) {
     
        // Define a hashmap
        HashMap<Integer, String> cities = new HashMap<>();
     
        // Adding key pair to hashmap  
        cities.put(101, "Delhi");
        cities.put(102, "New York");
        cities.put(103, "Peris");
        cities.put(104, "Denmark");
     
        // Print all hashmap key pairs
        System.out.println("HashMap: " + cities);
      }
    }

    Now, compile and run above Java program. You should see the results as below:

    Output:
    
HashMap: {101=Delhi, 102=New York, 103=Peris, 104=Denmark}

    Wrap Up

    In this faq, you have learned an example to get the HashMap key based on a value in the Java programming language.

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