Best way of chaining reduce with Java 8

Question

I have the following code that I'm trying to improve:

BigDecimal total = entity.getAssociate().stream().map(Associates::getPropertyA)     .reduce(BigDecimal.ZERO, BigDecimal::add); total = entity.getAssociate().stream().map(Associates::getPropertyB)     .reduce(total, BigDecimal::add); total = entity.getAssociate().stream().map(Associates::getPropertyC)     .reduce(total, BigDecimal::add); total = entity.getAssociate().stream().map(Associates::getPropertyD)     .reduce(total, BigDecimal::add); 

It works, but it really feels like there is a better way of doing this. Can anybody enlighten me on the matter?

Answer 1

If all these properties are of the same type (it seems they are all BigDecimal), you can use flatMap to create a single Stream of them all and then reduce it to the total sum:

BigDecimal total =      entity.getAssociate()           .stream()           .flatMap (a -> Stream.of(a.getPropertyA(),a.getPropertyB(),a.getPropertyC(),a.getPropertyD()))           .reduce(BigDecimal.ZERO, BigDecimal::add);