[SOLVED] Update list of object from another list keeping the order using lambda expressions in Java 8

Update list of object from another list keeping the order using lambda expressions in Java 8

I have two lists of objects. The object is a simple class contains key, value attributes.

I want to update the value of the first list from the second one. Replacing or cloning the list is not working because the ordering of the two lists are different and they should stay in their orders.

Any suggestions?

Example:

for(int i = 0 ; i < mValues.size() ; i++)
        {
            for (int j = 0 ; j < mValues.size() ; j++)
            {
                if(newData.get(i).getKey().equalsIgnoreCase(mValues.get(j).getKey()))
                {
                    mValues.get(j).setValue(newData.get(i).getValue());
                }
            }

        }

Demo:

myObject o1 = new myObject("k1" , 10);
myObject o2 = new myObject("k2" , 20);
myObject o3 = new myObject("k2" , 30);
myObject o4 = new myObject("k1" , 40);

List<myObject> l1 = new ArrayList<>();
List<myObject> l2 = new ArrayList<>();
l1.add(o1);
l1.add(o2);

l2.add(o3);
l2.add(o4);

Here should make the update to l1 based on l2 by looking for the key and update the value.

The result should look like:

l1 key is "k1" and value is 40 and next key is "k2" and the value is 30

Solution

I would use streams for that job.

Assuming your class MyObject has getters and setters methods defined (getKey(), getValue(), setKey(), setValue()), you can do:

l1.forEach(myObject1 -> l2.stream()
            .filter(myObject2 -> myObject1.getKey().equals(myObject2.getKey()))
            .findAny().ifPresent(myObject2 -> myObject1.setValue(myObject2.getValue())));

If you can have duplicate keys then you should modify ifPresent() to forEach():

l1.forEach(myObject1 -> l2.stream()
            .filter(myObject2 -> myObject1.getKey().equals(myObject2.getKey()))
            .forEach(myObject2 -> myObject1.setValue(myObject2.getValue())));