IfPresent function map

Question

How can I execute a function by the value of the card only if it is present, without making any changes to the card? I want to do this using the declarative style of "Java 8", comparable to Optional.ifPresent().

My use case is as follows:

I receive updates (new or deleted) for objects partially, I want to register these updates with my parent. For accounting, I have the following:

Map<ParentId, Parent> parents = ...

When I get a new baby, I do the following:

parents.computeIfAbsent(child.getParentId(), k -> new Parent()).addChild(child));

However, for deletion, I cannot find a declarative function. Straight ahead, I would implement this as:

if(parents.containsKey(child.getParentId())
{
     parents.get(child.getParentId()).removeChild(child);
}

Or I could wrap the value in Optional:

Optional.ofNullable(parents.get(child.getParentId()).ifPresent(p -> p.removeChild(child));

, Parent , , . , ( removeChild() Parent):

parents.computeIfPresent(child.getParentId(), (k, v) -> v.removeChild());

, Optional.ifPresent()?

Answer 1

, Optional ,

( removeChild() ): parents.computeIfPresent(child.getParentId(), (k, v) -> v.removeChild());

lambda

parents.computeIfPresent(child.getParentId(), (k, v) -> { v.removeChild(); return v; });

, , .

Answer 2

, , :

parents.getOrDefault(child.getParentId(), new Parent()).removeChild(child);