How to associate two ArrayLists of objects?

Question

Let's say I've got this two ArrayLists, the first one is of the type ObjectA, the second ObjectB.

These are ObjectA's variables:

 int id;
 double value;

And these are ObjectB's variables:

 int objAId;
 double disccountValue;

How can I retrieve the disccountValue of ObjectB where objAId is the same of the item on the first list? Just like in a SQL query, but in ArrayLists.

Possible duplicate of Merging two arrayLists into a new arrayList, with no duplicates and in order, in Java — jsoberg
– jsoberg, Commented Feb 15, 2016 at 18:15
You can override the equals method, and get the object index that contains the value. ifContains() and indexOf() — Pablo C. García
– Pablo C. García, Commented Feb 15, 2016 at 18:19
One solution is to do a linear search in listA based on a given objAId from an ObjectB. If you sort listA by the id value, you can improve the speed by doing a binary search instead. — Code-Apprentice
– Code-Apprentice, Commented Feb 15, 2016 at 19:55
Similarly if you want to search for something in listB, you can do either a linear or binary search depending on whether you sort the list before searching. — Code-Apprentice
– Code-Apprentice, Commented Feb 15, 2016 at 19:57

Dave · Accepted Answer · 2016-02-15 19:41:12Z

0

If you're trying to get the value for each object A:

for(ObjectA objA : arrayListOfObjectAs){
    int id = objA.id;
    for(ObjectB objB : arrayListOfObjectBs){
        if(id == objB.objAId){
            //do what you want with the objB.discountValue here
        break;
        }
    }
}

If you're only looking for a single id you can get rid of that outer for loop

answered Feb 15, 2016 at 19:41

Dave

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