How to iterate List of one object array and set to another object list in java 8?

Question

Currently I have list of object(Entitlement) array, from that array I have to Iterate and add to the list of Card object, any way to do this. Please let me know.

Now I don't want entire data from entitlements list, need only id and name and want this to be store into Card object. How i can achieve this, using stream?

public static class Entitlement {
   public String id;
   public String name;
   public String serviceEntitlementNumber;
   public String serviceType;
   public String alphaId;
   public String modifiedTime;
} //Entitlement obj – 


public static class Card { 
   public String id;
   public String name;
} // card obj

List <MerchantGatewayEntitlement> entitlements = 
       getEntitlements(merchantId);

List <Card> cards = new ArrayList <>();
 
for (MerchantGatewayEntitlement entitlement : entitlements) {
     how to add this list to card list.
}

Answer 1

Why use streams? It has its advantages but it also has quite a bit of overhead. Nothing wrong with using a loop. And don't worry about "improving" existing working code using Java 8 features.

I don't know what your Card class looks like but there is nothing wrong with the following:

List<Card> cardList = new ArrayList<>();
for (MerchantGatewayEntitlement entitlement : entitlements) {
   cardList.add(new Card(entitlement.getCard(), entitlement.getSomethingElse()));
}

or other Java 8 options.

entitlements.forEach(ent-> {
    cardList.add(new Card(ent.getCard(), ent.getSomethingElse()));
});

But if you insist on using a stream solution and you need to be able to modify the returned list, then do it like this.

List<Card> cardList = entitlements.stream()
     .map(ent -> new 
         Card(ent.getCard(),ent.getSomethingElse()))
     .collect(Collectors.toCollection(ArrayList::new));