Merge two elements of List into one element using Java 8

I have a List<Customer> where I can have 2 objects of same Customer. One object can have few attributes populated while another object has some other attributes populated . Is their any way using Java 8 where I can merge 2 objects into 1 object which all attributes populated and in final list add only that object. I have written below code it is serving my purpose but I want some more cleaner approach using Java 8.

       List<Customer> list = entry.getValue();
			if (StringUtils.hasLength(list.get(1).getID())) {
				list.get(0).setID(list.get(1).getID());
			}
			if (BigDecimal.ZERO.compareTo(list.get(1).getCreditAmount()) != 0) {
				list.get(0).setCreditAmount(list.get(1).getCreditAmount());
			}
			processedChargeTransactions.add(list.get(0));

Using Java 8:

Logic:

Here, I have converted the list into Map using Collectors.toMap function with the merger function. This merger function will check the value corresponding to the key for each attribute as shown in the if-else block and if value is null or not assigned, it will set the value from another key corresponding to each attribute.

Note: It will also work with multiple objects with same id and can have any number of attributes, you just need to update the if-else block corresponding to each attribute.

Code:

public class Test {
    public static void main(String[] args) {

        List<Customer> customers = new ArrayList<>();

        Customer c1 = new Customer();
        c1.setId(1);
        c1.setGender("Male");

        Customer c2 = new Customer();
        c2.setId(1);
        c2.setAddress("aaa");

        Customer c3 = new Customer();
        c3.setId(1);
        c3.setCreditAmount(100);

        customers.add(c1);
        customers.add(c2);
        customers.add(c3);

        System.out.println("list before merging:: " + customers);

        List<Customer> mergeList = customers.stream()
                .collect(Collectors.toMap(Customer::getId, Function.identity()
           ,(a, b) -> {
            if(a.getAddress() == null){
                a.setAddress(b.getAddress());
            }
            if(a.getCreditAmount() == 0.0){
                a.setCreditAmount(b.getCreditAmount());
            }
            if(a.getGender() == null){
                a.setGender(b.getGender());
            }
            return a;
        })).values().stream().toList();

        System.out.println("list after merging:: " + mergeList);
    }
}

Output:

list before merging:: [
Customer{id=1, creditAmount=0.0, address=null, gender=Male},
Customer{id=1, creditAmount=0.0, address=aaa, gender=null},
Customer{id=1, creditAmount=100.0, address=null, gender=null}
]
list after merging:: [Customer{id=1, creditAmount=100.0, address=aaa, gender=Male}]

Use the Stream's reduce method to merge the attributes of the two Customer objects.

Initialize the reduction with a new Customer object, and then iterate through the list using reduce.

For every element in the list, check if the attributes are present then merge them into the initial Customer object. The final result of the reduce operation will be the merged Customer object.

List<Customer> list = entry.getValue();
if (list.size() == 2) {
    Customer mergedCustomer = list.stream()
            .reduce(new Customer(), (customer1, customer2) -> {
                if (StringUtils.hasLength(customer2.getID())) {
                    customer1.setID(customer2.getID());
                }
                if (BigDecimal.ZERO.compareTo(customer2.getCreditAmount()) != 0) {
                    customer1.setCreditAmount(customer2.getCreditAmount());
                }
                return customer1;
            });
    processedChargeTransactions.add(mergedCustomer);
}