public class Main {

    public static void main(String[] args) {

        // 给一个有普通收入、写作收入的小伙伴算税:

        Income[] incomes = new Income[] {

            new Income(3000),

            new Write(5000),

        };

        System.out.println(totalTax(incomes));

    }

    public static double totalTax(Income... incomes) {

        double total = 0;

        for (Income income: incomes) {

            total = total + income.getTax();

        }

        return total;

    }

}

class Income {

    protected double income;

    public Income(double income) {

        this.income = income;

    }

    public double getTax() {

        return income * 0.1; // 税率10%

    }

}

class Write extends Income {

    public Write(double income) {

        super(income);

    }

    @Override

    public double getTax() {

        if (income <= 5000) {

            return 0;

        }

        return (income - 5000) * 0.2;

    }

}