Properties computeIfAbsent(Key, Function) method in Java with Examples
The computeIfAbsent(Key, Function) method of Properties 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).
- 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.
Syntax:
public Object computeIfAbsent?(Object key,
Function mappingFunction)
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 current (existing or computed) 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 computeIfAbsent(Key, Function) method:
Program 1:
// Java program to demonstrate// computeIfAbsent(Key, Function) 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 value for new key which is absent        // using computeIfAbsent method        properties.computeIfAbsent("newPen", k -> 600);        properties.computeIfAbsent("newBook", k -> 800);          // print new mapping        System.out.println("New Properties: "                           + properties.toString());    }} |
Output:
Current Properties: {Book=500, Mobile=5000, Pen=10, Clothes=400}
New Properties: {newPen=600, Book=500, newBook=800, Mobile=5000, Pen=10, Clothes=400}
Program 2:
// Java program to demonstrate// computeIfAbsent(Key, Function) 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 value for new key which is absent        // using computeIfAbsent method        properties.computeIfAbsent(4, k -> "600RS");          // this will not effect anything        // because key 1 is present        properties.computeIfAbsent(1, k -> "800RS");          // print new mapping        System.out.println("New Properties: "                           + properties.toString());    }} |
Output:
Current Properties: {3=1000RS, 2=500RS, 1=100RS}
New Properties: {4=600RS, 3=1000RS, 2=500RS, 1=100RS}
