update field when others fields are motifed

jennifer lawrence :

I have a class Installment and a method executeTransaction. The field totalBalance represents the difference between total due and total paid. Inside method executeTransaction the installment object is modified using setters. And after every setter the updateTotalBalance is called.

    public class Installment {
        private BigDecimal principalDue;
        private BigDecimal principalPaid;
        private BigDecimal interestDue;
        private BigDecimal interestPaid;
        private BigDecimal feeDue;
        private BigDecimal feePaid;
        private BigDecimal penaltyDue;
        private BigDecimal penaltyPaid;
        private BigDecimal totalBalance;

        public void updateTotalBalance() {
             this.totalBalance = this.principalDue.subtract(this.penaltyPaid)
                .add(this.interestDue).subtract(this.interestPaid)
                .add(this.feeDue).subtract(this.feePaid)
                .add(this.penaltyDue).subtract(this.penaltyPaid);
        }

        //seters
        //getters
    }

Transaction method:


    public void executeTransaction(Installment installment){
        //code
        installment.setPrincipalPaid(bigDecimalValue);
        installment.updateTotalBalance();
        //code
        installment.setPenaltyDue(bigDecimalValue);
        installment.updateTotalBalance();
    }

I was thinking about putting the updateTotalBalance inside the setters, but for me both of these approaches seem contradictory with the best design principles. Q: I want to know if there are better solutions to update a field in a class when others fields are modified.

bubbles :

You can follow the single responsibility principle by isoliting (delegating) the calculation in another object and keep the Installment as a simple POJO.

public class Calculator {

    public BigDecimal balance(Installment installment) {
        return installment.getPrincipalDue().subtract(installment.getPenaltyPaid())
                .add(installment.getInterestDue()).subtract(installment.getInterestPaid())
                .add(installment.getFeeDue()).subtract(installment.getFeePaid())
                .add(installment.getPenaltyDue()).subtract(installment.getPenaltyPaid());
    }
}

import java.math.BigDecimal;

@Value
public class Installment {
    private BigDecimal principalDue;
    private BigDecimal principalPaid;
    private BigDecimal interestDue;
    private BigDecimal interestPaid;
    private BigDecimal feeDue;
    private BigDecimal feePaid;
    private BigDecimal penaltyDue;
    private BigDecimal penaltyPaid;
}