package com.company;

public class Main {
    public static void main(String[] args) {
        Income[] incomes = new Income[]{
              new Income(3000),
              new Salary(7500),
                new State(15000)
        };
        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
            }
        }
        class Salary extends Income{
            public Salary(double income){
                super(income);
            }
            @Override
            public double getTax(){
                if(income<=5000)
                return 0;
            return (income-5000)*0.2;
            }
}

        class State extends Income{
            public State(double income){
                super(income);
            }
            @Override
            public double getTax(){
                return 0;
            }
        }
输出：123
Switch问题。待解决。