如何在java中比较继承中的两个值？

Question

我试图创建一个程序，检查哪个帐户的成本最低，但我不知道如何在我的程序中实现这一点

我想分别选择每个类的输出来比较(dayTimeCost)

这是我认为它可能会实现的，但我不知道如何实现

if (BronceDayTimeCost < SilverDayTimeCost){ System.out.print("\nThe Bronze Account is cheapest.");}

if (SilverDayTimeCost< BronceDayTimeCost ){ System.out.print("\nThe Silver Account is cheapest.");}

青铜级

    public  class Bronze  {

    // ----------------- Atributes -----------------------

    

    public int dayMinutes;      // daytime telphone minutes used

    public double dayTimeCost;  //Total daytime calls cost

    // ------------- CONSTRUCTORS (inputs) ---------------

    public Bronze(int theDayMinutes ) {  
    dayMinutes = theDayMinutes; 
    }
    // ------------------ METHODS ------------------------
    // Calculate Total daytime calls cost
    public double calcDayTimeCost(double costDay) {

        dayTimeCost = dayMinutes * costDay;
        System.out.print("\nCost of daytime calls = "  + costDay + "/min"+
        "\n\nTotal daytime calls cost = " + dayTimeCost + 
        "\n");

        return dayTimeCost;
    }

    //toString method to override that in Object
    public String toString(){
    return(
 "\n" 
         );
    }

    //Returns the type of account
    public String type(){
    return "Bronze";
    }
}

银牌级别

   public class Silver extends Bronze {

    private static final double costDay = 0.22;

    public Silver(int theDayMinutes ) {
    super(theDayMinutes );

  }
    //Returns the type of account
    public String type(){
    return "Silver";
    }

}

主类

    import java.util.Scanner;

public class AccountUser {

    // ------------------- FIELDS ------------------------    

    // Create instance of Scanner class
    public static Scanner input = new Scanner(System.in);
    // variables
    public static Bronze bron;
    public static Silver silv;

    public static int dayMinutes;

    // ------------------ METHODS ------------------------  

    public static void main(String [] args) {

        // Input dayMinutes (with error message)
        do{
        System.out.print("Please daytime telphone minutes used --> ");
        dayMinutes  = input.nextInt();
        if  ( dayMinutes <= 0){System.out.print("\n" + "Input value outside the range!!!" + "\n");}
        }while( dayMinutes <= 0);


        // Create new Bronze instance
        bron = new Bronze(dayMinutes);
        silv = new Silver(dayMinutes);
        // Calculate scheme1, scheme2
        bron.calcDayTimeCost(0.12);
        silv.calcDayTimeCost(0.22);


    System.out.println(bron);
    System.out.println(silv);
    }
}

Answer 1

您可以将calcDayTimeCost方法的return类型收集到如下所示的double变量中，然后使用if和else条件检查哪种成本更低

double bronCost = bron.calcDayTimeCost(0.12);
double silverCost = silv.calcDayTimeCost(0.22);
if(bronCost == silverCost) {
    System.out.print("\nThe Silver and Bronze Accounts are same cost ");
} else if (bronCost < silverCost){ 
     System.out.print("\nThe Bronze Account is cheapest.");
} else {
     System.out.print("\nThe Silver Account is cheapest.");
}

虽然您的代码可以工作，但它不与面向对象编程相关联，也就是说，一般来说，我们创建的类与现实世界中的对象相关联，但是Bronze和Silver两个不同的元素，即它们不直接相互关联/继承

换句话说，当你说ClassA{}{}时，你是说ClassA是一个ClassB

因此，替代方法如下：

  public abstract class Metal {

        //add fields applicable for all metals  

        public double calcDayTimeCost() {
             //add code here
        }
    }

  public class Bronze extends Metal {

       //Bronze specific details
  }

  public class Silver extends Metal {

       //Silver specific details
  }