The computeIfPresent(Key, BiFunction) method of Properties class which allows you to compute value of a mapping for specified key if key is already associated with a value (or is mapped to null).
- If mapping function of this method returns null, the mapping is removed.
- If the remapping function throws an exception, the exception is rethrown, and the mapping is left unchanged.
- 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 Object computeIfPresent?(Object key,
BiFunction 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 remapped value associated with the specified key, or null if mapping returns null.
Exception: This method throws ConcurrentModificationException if it is detected that the remapping function modified this map.
Below programs illustrate the computeIfPresent(Key, BiFunction) method:
Program 1:
// Java program to demonstrate// computeIfPresent(Key, BiFunction) method.  import java.util.*;  public class GFG {      // Main method    public static void main(String[] args)    {          // Create a properties and add some values        Properties properties = new Properties();        properties.put("Pen", 10);        properties.put("Book", 500);        properties.put("Clothes", 400);        properties.put("Mobile", 5000);          // print Properties details        System.out.println("Current Properties: "                           + properties.toString());          // provide new value for keys which is present        // using computeIfPresent method        properties.computeIfPresent("Pen", (key, val)                                               -> 600);        properties.computeIfPresent("Book", (key, val)                                                -> 800);          // print new mapping        System.out.println("New Properties: "                           + properties.toString());    }} |
Output:
Current Properties: {Book=500, Mobile=5000, Pen=10, Clothes=400}
New Properties: {Book=800, Mobile=5000, Pen=600, Clothes=400}
Program 2:
// Java program to demonstrate// computeIfPresent(Key, BiFunction) method.  import java.util.*;  public class GFG {      // Main method    public static void main(String[] args)    {          // Create a properties and add some values        Properties properties = new Properties();          properties.put(1, "100RS");        properties.put(2, "500RS");        properties.put(3, "1000RS");          // print Properties details        System.out.println("Current Properties: "                           + properties.toString());          // provide new value for key which is present        // using computeIfPresent method        properties.computeIfPresent(3, (key, val)                                           -> "00RS");          // this will not effect anything        // because key 4 is absent        properties.computeIfPresent(4, (key, val)                                           -> "$");          // print new mapping        System.out.println("New Properties: "                           + properties.toString());    }} |
Output:
Current Properties: {3=1000RS, 2=500RS, 1=100RS}
New Properties: {3=00RS, 2=500RS, 1=100RS}
