The computeIfAbsent(Key, Function) method of HashMap class is used to compute value for a given key using the given mapping function, if key is not already associated with a value (or is mapped to null) and enter that computed value in Hashmap else null.
- If mapping function of this method returns null, then no mapping is recorded for that key.
- At time of computation if remapping function throws an exception, the exception is rethrown, and the no mapping is recorded.
- During computation, modification this map using this method is not allowed.
- This method will throw a ConcurrentModificationException if the remapping function modified this map during computation.
Syntax:
public V
computeIfAbsent(K key,
Function<? super K, ? extends V> remappingFunction)
Parameters: This method accepts two parameters:
key : key for which we want to compute value using mapping.
remappingFunction : function to do the operation on value.
Returns: This method returns current (existing or computed) value associated with the specified key, or null if mapping returns null.
// Java program to demonstrate
// computeIfAbsent(Key, Function) method.
import java.util.*;
public class GFG {
// Main method
public static void main(String[] args)
{
// create a HashMap and add some values
HashMap<String, Integer> map
= new HashMap<>();
map.put("key1", 10000);
map.put("key2", 55000);
map.put("key3", 44300);
map.put("key4", 53200);
// print map details
System.out.println("HashMap:\n "
+ map.toString());
// provide value for new key which is absent
// using computeIfAbsent method
map.computeIfAbsent("key5",
k -> 2000 + 33000);
map.computeIfAbsent("key6",
k -> 2000 * 34);
// print new mapping
System.out.println("New HashMap:\n "
+ map);
}
}
OutPut:
HashMap:
{key1=10000, key2=55000, key3=44300, key4=53200}
New HashMap:
{key1=10000, key2=55000, key5=35000, key6=68000, key3=44300, key4=53200}