Hashtable computeIfAbsent() method in Java with Examples
Last Updated :
30 Oct, 2018
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The computeIfAbsent(Key, Function) method of Hashtable class which allows you to compute value of a mapping for specified key if key is not already associated with a value (or is mapped to null).
Java
Java
- If mapping function of this method returns null, then no mapping is recorded.
- If the 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.
public V
computeIfAbsent(K key,
Function<? super K, ? extends V> remappingFunction)
Parameters: This method accepts two parameters:
- key: key with which the value is to be associated.
- remappingFunction: function to do the operation on value.
- ConcurrentModificationException: if it is detected that the remapping function modified this map.
// Java program to demonstrate
// computeIfAbsent(Key, Function) method.
import java.util.*;
public class GFG {
// Main method
public static void main(String[] args)
{
// create a table and add some values
Map<String, Integer> table = new Hashtable<>();
table.put("Pen", 10);
table.put("Book", 500);
table.put("Clothes", 400);
table.put("Mobile", 5000);
// print map details
System.out.println("hashTable: "
+ table.toString());
// provide value for new key which is absent
// using computeIfAbsent method
table.computeIfAbsent("newPen", k -> 600);
table.computeIfAbsent("newBook", k -> 800);
// print new mapping
System.out.println("new hashTable: "
+ table);
}
}
Output:
Program 2:
hashTable: {Book=500, Mobile=5000, Pen=10, Clothes=400}
new hashTable: {newPen=600, Book=500, newBook=800, Mobile=5000, Pen=10, Clothes=400}
// Java program to demonstrate
// computeIfAbsent(Key, Function) method.
import java.util.*;
public class GFG {
// Main method
public static void main(String[] args)
{
// create a table and add some values
Map<Integer, String> table = new Hashtable<>();
table.put(1, "100RS");
table.put(2, "500RS");
table.put(3, "1000RS");
// print map details
System.out.println("hashTable: "
+ table.toString());
// provide value for new key which is absent
// using computeIfAbsent method
table.computeIfAbsent(4, k -> "600RS");
// this will not effect anything
// because key 1 is present
table.computeIfAbsent(1, k -> "800RS");
// print new mapping
System.out.println("new hashTable: "
+ table);
}
}
Output:
References: https://docs.oracle.com/javase/10/docs/api/java/util/Hashtable.html#computeIfAbsent(K, java.util.function.Function)
hashTable: {3=1000RS, 2=500RS, 1=100RS}
new hashTable: {4=600RS, 3=1000RS, 2=500RS, 1=100RS}
