List uses stream flow to add according to the number of certain attributes of the element

Need to be on a List Remove duplicate unique value attributes of objects in , Attribute summation , The object is assumed to be BillsNums, Yes id、nums、sums Three attributes , among id Represents a unique value , need nums And sums In sum , And finally keep one .
For example, ：(“s1”, 1, 1),(“s1”,2,3),(“s2”,4,4), Sum and remove the weight , Namely (“s1”, 3, 4),(“s2”,4,4)

Objects and properties
class BillsNums {
    private String id;
    private int nums;
    private int sums;
    
    public String getId() {
        return id;
    }
    public void setId(String id) {
        this.id = id;
    }
    public int getNums() {
        return nums;
    }
    public void setNums(int nums) {
        this.nums = nums;
    }
    public int getSums() {
        return sums;
    }
    public void setSums(int sums) {
        this.sums = sums;
    }
}

data
public static void main(String[] args) {
 
    List<BillsNums> billsNumsList = new ArrayList<>();
    BillsNums billsNums = new BillsNums();
    billsNums.setId("1001");
    billsNums.setNums(2);
    billsNums.setSums(100);
    billsNumsList.add(billsNums);
 
    BillsNums billsNums2 = new BillsNums();
    billsNums2.setId("1001");
    billsNums2.setNums(3);
    billsNums2.setSums(100);
    billsNumsList.add(billsNums2);
 
    List<BillsNums> result = merge(billsNumsList);
    System.out.println("result:" + JSON.toJSONString(result, true));
}

/**
 * take id A merger nums, sums The set after adding a round and using Java8 Process the stream
 */
public static List<BillsNums> merge(List<BillsNums> list) {
        List<BillsNums> result = list.stream()
        // Express id by key, Then if there is a repetition , So from BillsNums object o1 And o2 Filter out one , Choose here o1,
        // And put id repeat , Need to put nums and sums And o1 To merge o2, Assign a value to o1, Finally back to o1
        .collect(Collectors.toMap(BillsNums::getId, a -> a, (o1,o2)-> {
            o1.setNums(o1.getNums() + o2.getNums());
            o1.setSums(o1.getSums() + o2.getSums());
            return o1;
        })).values().stream().collect(Collectors.toList());
        return result ;
}