The syntax of the compute()
method is:
hashmap.compute(K key, BiFunction remappingFunction)
Here, hashmap is an object of the HashMap class.
compute() Parameters
The compute()
method takes 2 parameters:
- key - key with which the computed value is to be associated
- remappingFunction - function that computes the new value for the specified key
Note: The remappingFunction can take two arguments. Hence, considered as BiFunction
.
compute() Return Value
- returns the new value associated with the key
- returns
null
if no value associated with key
Note: If remappingFunction results null
, then the mapping for the specified key is removed.
Example: HashMap compute() to Insert New Value
import java.util.HashMap;
class Main {
public static void main(String[] args) {
// create an HashMap
HashMap<String, Integer> prices = new HashMap<>();
// insert entries to the HashMap
prices.put("Shoes", 200);
prices.put("Bag", 300);
prices.put("Pant", 150);
System.out.println("HashMap: " + prices);
// recompute the value of Shoes with 10% discount
int newPrice = prices.compute("Shoes", (key, value) -> value - value * 10/100);
System.out.println("Discounted Price of Shoes: " + newPrice);
// print updated HashMap
System.out.println("Updated HashMap: " + prices);
}
}
Output
HashMap: {Pant=150, Bag=300, Shoes=200} Discounted Price of Shoes: 180 Updated HashMap: {Pant=150, Bag=300, Shoes=180
In the above example, we have created a hashmap named prices. Notice the expression,
prices.compute("Shoes", (key, value) -> value - value * 10/100)
Here,
- (key, value) -> value - value * 10/100 - It is a lambda expression. It reduces the old value of Shoes by 10% and returns it. To learn more about the lambda expression, visit Java Lambda Expressions.
- prices.compute() - Associates the new value returned by lambda expression to the mapping for Shoes.
We have used lambda expression as remapping function that rakes two parameters.
Note: According to the official documentation of Java, the HashMap merge() method is simpler than the compute()
method.
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