java - 如何记录以前的参数值并添加到新参数值？

Question

我想记录一个参数的旧值并在旧参数上添加新的参数值，我该如何在 java 中做到这一点？

例如，如何将 auto.fillUp 中的“10”和 auto.fillUp 中的“20”相加？

public class Main {
    public static void main(String[] args){
         OdometerReading auto = new OdometerReading(15);
         auto.fillUp(350, 10);
         auto.fillUp(450, 20);
         System.out.println("Miles per gallon: " + auto.calculateMPG());
    }
}

里程表阅读类：

public class OdometerReading {
    public int myStartMiles;
    public int myEndMiles;
    public double myGallonsUsed;
    public int milesInterval;
    public double getMyGallonsUsedNew;

    public OdometerReading(int assignedCarMiles){
       myStartMiles = assignedCarMiles;
       System.out.println("New car odometer reading: " + myStartMiles);
    }

    public void fillUp(int milesDriven, double gallonsUsed){
        myEndMiles = milesDriven;
        myGallonsUsed = gallonsUsed;
    }

    public double calculateMPG(){
        milesInterval = myEndMiles - myStartMiles;
        double mpg = milesInterval / myGallonsUsed;
        return mpg;
    }

    public void reset(){
        myStartMiles = myEndMiles;
        myGallonsUsed = 0;
    }

} 

***注意：我是 Java 和编程的初学者，如果这可能是一个“不专业”的问题，我很抱歉。

Answer 1

只需在方法中进行操作，状态就会保存在对象变量中，只要您有对对象的引用就可以了。

public void fillUp(int milesDriven, double gallonsUsed){
    myEndMiles += milesDriven;
    myGallonsUsed += gallonsUsed;
}

注意 + 运算符