考虑一下，我有下面的课.
public class Employee {
private Integer id;
private Integer parentId;
private int value;
}
现在我有以下记录.
Employee employee1 = new Employee(1, null, 4);
Employee employee2 = new Employee(2, 1, 4);
Employee employee3 = new Employee(3, null, 8);
Employee employee4 = new Employee(4, 1, 3);
Employee employee5 = new Employee(5, 2, 11);
所以parentId是employee中的id，而employee是另一个employee的老板.
问题是找出employee的值的100和它的父级(如果有)，或者按原样返回值.所以在这种情况下，结果应该是.
| id | value |
|---|---|
| 1 | 4 |
| 2 | 8 |
| 3 | 8 |
| 4 | 7 |
| 5 | 15 |
如何使用Java8流实现这一点？我试过以下方法:；
Optional<Integer> first = employees.stream().map(a -> {
int sum = 0;
employees.stream().map(b -> {
if (Objects.equals(a.id, b.parentId)) {
sum = sum + a.value + b.value;
}else{
sum = sum + a.value;
}
return sum;
});
return sum;
}
).findFirst();
但是我得到了sum变量的错误，它应该是final或者实际上是final.