Java HashMap computeIfAbsent() Method

Java HashMap

The computeIfAbsent() method recalculates the value for a specified key in the hashMap if it is not already present, and adds it to the hashMap.

The syntax for the computeIfAbsent() method is:

hashmap.computeIfAbsent(K key, Function remappingFunction)

Note: hashmap is an object of the HashMap class.

Parameter Description:

key - the key
remappingFunction - the remapping function used to recalculate the value

Return Value

If the value for the key does not exist, it uses the remappingFunction to calculate the new value and stores it as the value for the key; otherwise, it returns the existing value.

Example

The following example demonstrates the use of the computeIfAbsent() method:

Example

import java.util.HashMap;

class Main {
    public static void main(String[] args) {
        // Create a HashMap
        HashMap&lt;String, Integer> prices = new HashMap<>();

        // Add mappings to the HashMap
        prices.put("Shoes", 200);
        prices.put("Bag", 300);
        prices.put("Pant", 150);
        System.out.println("HashMap: " + prices);

        // Calculate the price for Shirt
        int shirtPrice = prices.computeIfAbsent("Shirt", key -> 280);
        System.out.println("Price of Shirt: " + shirtPrice);

        // Print the updated HashMap
        System.out.println("Updated HashMap: " + prices);
    }
}

Executing the above program outputs:

HashMap: {Pant=150, Bag=300, Shoes=200}
Price of Shirt: 280
Updated HashMap: {Pant=150, Shirt=280, Bag=300, Shoes=200}

In the above example, we created a HashMap named prices.

Note the expression:

prices.computeIfAbsent("Shirt", key -> 280)

In the code, we used the lambda expression key -> 280 as the remapping function. The prices.computeIfAbsent() method associates the new value returned by the lambda expression with "Shirt".

Since "Shirt" does not exist in the HashMap, a new key/value pair is added.

For more information about lambda expressions, visit Java Lambda Expressions.

When the key already exists:

Example

import java.util.HashMap;

class Main {
    public static void main(String[] args) {
        // Create a HashMap
        HashMap&lt;String, Integer> prices = new HashMap<>();

        // Add mappings to the HashMap
        prices.put("Shoes", 180);
        prices.put("Bag", 300);
        prices.put("Pant", 150);
        System.out.println("HashMap: " + prices);

        // The mapping for Shoes already exists
        // No new value is calculated for Shoes
        int shoePrice = prices.computeIfAbsent("Shoes", (key) -> 280);
        System.out.println("Price of Shoes: " + shoePrice);

        // Print the updated HashMap
        System.out.println("Updated HashMap: " + prices);
    }
}

Executing the above program outputs:

HashMap: {Pant=150, Bag=300, Shoes=180}
Price of Shoes: 180
Updated HashMap: {Pant=150, Bag=300, Shoes=180}

// Output the updated HashMap
System.out.println("Updated HashMap: " + prices);
}
}

The output of the above program is:

HashMap: {Pant=150, Bag=300, Shoes=180}
Price of Shoes: 180
Updated HashMap: {Pant=150, Bag=300, Shoes=180}

In the above example, the mapping for Shoes already exists in the HashMap, so a new value is not calculated for Shoes.

Java HashMap ```

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