Java 代码

import java.util.Scanner;

public class Main
{
    public static double calcTax(double income, double base, double limit, double taxRate)
    {
        if (income - base > limit && limit > -1)
            return limit * taxRate;
        else
            return (income - base )*taxRate;
    }

    public static void main(String[] args)
    {
        Scanner cin = new Scanner(System.in);

        double income = cin.nextDouble();
        double tax = 0.0;

        if (income > 2000)
            tax += calcTax(income, 2000.0, 1000.0, 0.08);

        if (income > 3000)
            tax += calcTax(income, 3000.0, 1500.0, 0.18);  

        if (income > 4500)
            tax += calcTax(income, 4500.0, -1, 0.28);  

        if (tax == 0.0)
            System.out.println ("Isento");
        else
            System.out.println ("R$ " + String.format("%.2f", tax));
    }
}