How to sum multiple fields of a list of objects using stream in java - spring-boot

Question

I'm trying to get the sums of two fields from a Model class. and return it using using a pojo but kept getting syntax errors. What I am trying to achieve is similar to the highest voted answer in This: Summing multiple different fields in a list of objects using the streams api? but I got syntax error. Here is my model:
public class BranchAccount {
#NotNull(message = "Account balance is required")
private Double accountBalance;
#NotNull(message = "Profit is required")
private Double profit;
#Temporal(TemporalType.TIMESTAMP)
private Date dateCreated;
#Temporal(TemporalType.TIMESTAMP)
private Date lastUpdated;
}
My Pojo:
public class ProfitBalanceDto {
private Double accountBalance;
private Double profit;
}
My code to get sum of accountBalance and profit from BranchAccount:
public ProfitBalanceDto getAllBranchAccount() {
List<BranchAccount> branchAccounts = branchAccountRepository.findAll();
branchAccounts.stream()
.reduce(new ProfitBalanceDto(0.0, 0.0), (branchAccount1, branchAccount2) -> {
return new ProfitBalanceDto(
branchAccount1.getAccountBalance() + branchAccount2.getAccountBalance(),
branchAccount1.getProfit() + branchAccount2.getProfit());
});
return null;
}
My errors:
Please am I doing wrong?
PS: I want to use stream for this.

Answer 1

As #Holger mentioned in his comment, you can map to ProfitBalanceDto before reducing
public ProfitBalanceDto getAllBranchAccount2() {
List<BranchAccount> branchAccounts = branchAccountRepository.findAll();
return branchAccounts.stream()
.map(acc -> new ProfitBalanceDto(acc.getAccountBalance(), acc.getProfit()))
.reduce(new ProfitBalanceDto(0.0, 0.0),
(prof1, prof2) -> new ProfitBalanceDto(prof1.getAccountBalance()+ prof2.getAccountBalance(),
prof1.getProfit() + prof2.getProfit()));
}
If you are using Java 12 or higher using the teeing collector might be a better option
public ProfitBalanceDto getAllBranchAccount() {
List<BranchAccount> branchAccounts = branchAccountRepository.findAll();
return branchAccounts.stream()
.collect(Collectors.teeing(
Collectors.summingDouble(BranchAccount::getAccountBalance),
Collectors.summingDouble(BranchAccount::getProfit),
ProfitBalanceDto::new));
}