HashMap computeIfPresent() method in Java with Examples
The computeIfPresent(Key, BiFunction) method of HashMap class is used to update value in a key-value pair in the map. If key does not exist then it does not do any thing.
Syntax
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V computeIfPresent(K key,
BiFunction<? super K, ? super V, ? extends V> remappingFunction) Example
Following is an example of computeIfAbsent invocation and its results.
ComputeIfAbsentExample
package corejava.map;
import java.util.HashMap;
import java.util.Map;
public class ComputeIfPresentExample {
public static void main (String argv[]) {
Map<String, Integer> map = new HashMap<String, Integer>();
map.put("Sunglass", 105);
map.put("Watch", 1501);
newline("Original Map");
map.forEach((a, b) -> {
System.out.println(a + " -> " + b);
});
map.computeIfPresent("Watch", (k,v) -> {return v + v;});
newline("After calling computeIfAbsent Map");
map.forEach((a, b) -> {
System.out.println(a + " -> " + b);
});
}
static void newline(String s) {
System.out.println("\n" + s);
};
}
Output of above program.
Original Map Watch -> 1501 Sunglass -> 105 After calling computeIfAbsent Map Watch -> 3002 Sunglass -> 105
Summary
computeIfPresent helps in writing more compact code and also make code more readable.
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