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javaarraylisthashmap

How to sort an ArrayList using a Map key as list object and value as the order?

I need to keep the order of my list of objects as it can be changed and reordered anytime in my webapp.

In my model I have a array list of objects example 

objectList = [object1, object2, object3, object4]

and I save the order of each object belonging to this instance to a Map example: order 

{
   "object1":4,
   "object2":2,
   "object3":1,
   "object4":3
}

Therefore i want to sort my array according to its value in the map retrieved by the objects Id as the key:

Expected result:

[object3, object2, object4, object1]

How would I go about doing this?

Solution

  • Assuming your objects have a getter for the id getId(), then you can make use of the Comparator.comparing() helper method, which creates a comparator for the provided lambda:

    objectList.sort(Comparator.comparing(o -> yourMap.get(o.getId()));

    This effectively the same as writing your own Comparator or writing your own compare method.