HashTable compute() method in Java with Examples
Last Updated :
02 Jun, 2023
The compute(Key, BiFunction) method of Hashtable class allows to compute a mapping for the specified key and its current mapped value (or null if there is no current mapping is found).
- If the remapping function passed in compute() of Hashtable returns null as a return value then the mapping is removed from Hashtable(or remains absent if initially absent).
- If the remapping function throws an exception, the exception is rethrown, and the current mapping is left unchanged.
- During computation, modification this map using this method is not allowed.
- The compute() method can be used to update an existing value inside Hashtable. For example, This mapping append string value of mapping:
Hashtable.compute(key, (k, v) -> v.append("strValue"))- This method will throw a ConcurrentModificationException if the remapping function modified this map during computation.
Syntax:
public V
compute(K key,
BiFunction<? super K, ? super V, ? 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.
Returns: This method returns new value associated with the specified key, or null if none.
Exception: This method throws:
- ConcurrentModificationException: if it is detected that the remapping function modified this map.
Below programs illustrate the compute(Key, BiFunction) method:
Program 1:
Java
// Java program to demonstrate
// compute(Key, BiFunction) 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());
// remap the values of hashTable
// using compute method
table.compute("Pen", (key, val)
-> val + 15);
table.compute("Clothes", (key, val)
-> val - 120);
// print new mapping
System.out.println("new hashTable: " + table);
}
}
Output:hashTable: {Book=500, Mobile=5000, Pen=10, Clothes=400}
new hashTable: {Book=500, Mobile=5000, Pen=25, Clothes=280}
Program 2:
Java
// Java program to demonstrate
// compute(Key, BiFunction) 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());
// remap the values of hashTable
// using compute method
table.compute(3, (key, val)
-> val.substring(0, 4) + "00RS");
table.compute(2, (key, val)
-> val.substring(0, 2) + "$");
// print new mapping
System.out.println("new hashTable: " + table);
}
}
Output:hashTable: {3=1000RS, 2=500RS, 1=100RS}
new hashTable: {3=100000RS, 2=50$, 1=100RS}
References: https://docs.oracle.com/javase/10/docs/api/java/util/Hashtable.html#compute(K, java.util.function.BiFunction)