Flash cards
Review the key moves
What is the main idea behind Java HashMap computeIfPresent() Method?
Lesson checks
Practice each idea before moving on
Short Mimo-style checks built from this lesson's code, terms, and sequence.
Which statement best captures the main point of this lesson?
Complete the missing token from the example code.
___ java.util.HashMap;Put the learning moves in the order that makes the concept easiest to apply.
❮ HashMap Methods
Example
import java.util.HashMap;
public class Main {
public static void main(String[] args) {
HashMap<String, String> capitalCities = new HashMap<String, String>();
capitalCities.put("England", "London");
capitalCities.put("Germany", "Berlin");
capitalCities.put("Norway", "Oslo");
capitalCities.put("USA", "Washington DC");
capitalCities.computeIfPresent("England", (k, v) -> v + "(" + k + ")");
System.out.println(capitalCities);
}
}Definition and Usage
The computeIfPresent() method calculates a value for an entry based on its key. If an entry with the specified key does not exist or its value is null then the map is not changed.
The value is computed using a function, which can be defined by a lambda expression that is compatible with the apply() method of Java's BiFunction interface.
To learn about lambda expressions, see our Java Lambda Expression tutorial .
Syntax
public void computeIfPresent(K
key , BiFunction
function )K refers to the data type of the keys of the map.
Parameter Values
| Parameter | Description |
|---|---|
| key | Required. Specifies the key of the entry. |
| function | Required. A Function object or lambda expression which computes the value of the entry. The first parameter of the function contains the key of an entry and the second parameter contains its value. |
Technical Details
| Returns: | The value computed by the function or null if the map is not changed. |
|---|