HashMap computeIfAbsent() method in Java with Examples
The computeIfAbsent(Key, Function) method of HashMap class is used to enter a new key-value pair to map if the key does not exist. If key exists then it does not do any thing.
Syntax
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public V computeIfAbsent(K key, Function<? super K, ? 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 ComputeIfAbsentExample {
public static void main (String argv[]) {
Map<Integer, String> map = new HashMap<Integer, String>();
map.put(1, "one");
map.put(2, "two");
map.put(3, "three");
map.put(4, "four");
map.put(5, "five");
newline("Original Map");
map.forEach((a, b) -> {
System.out.println(a + " -> " + b);
});
map.computeIfAbsent(6, k-> { return "six";});
map.computeIfAbsent(7, k -> "seven");
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 1 -> one 2 -> two 3 -> three 4 -> four 5 -> five After calling computeIfAbsent Map 1 -> one 2 -> two 3 -> three 4 -> four 5 -> five 6 -> six 7 -> seven
Summary
computeIfAbsent helps in writing more compact code and also make code more readable.
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