命名私有实例变量

Question

我用Java编写这两个文件，我的老师说它们工作正常，但我需要减少代码中私有实例变量的数量。你怎么会修这个呢？

public class CarV7 {

    private String myCarType1, myCarType2, myCarType3;
    private int mySmiles1, mySmiles2, mySmiles3;
    private int myEmiles1, myEmiles2, myEmiles3;
    private double myGals1, myGals2, myGals3;
    private double myPricePerGallon1, myPricePerGallon2, myPricePerGallon3;

    CarV7(String carType, int eMiles, int sMiles, double gals, double pricePerGallon) {
        myCarType1 = carType;
        myCarType2 = carType;
        myCarType3 = carType;
        mySmiles1 = sMiles;
        mySmiles2 = sMiles;
        mySmiles3 = sMiles;
        myEmiles1 = eMiles;
        myEmiles2 = eMiles;
        myEmiles3 = eMiles;
        myGals1 = gals;
        myGals2 = gals;
        myGals3 = gals;
        myPricePerGallon1 = pricePerGallon;
        myPricePerGallon2 = pricePerGallon;
        myPricePerGallon3 = pricePerGallon;
    }

    public int calcDistance(int myEmiles, int sMiles) {
        return myEmiles - sMiles;
    }

    public double calcMPG(int distance, double gals) {
        return distance / gals;
    }

    public double calcGPM(double myGals, int distance) {
        return myGals / distance;
    }

    public double totalCost(double pricePerGallon, double gals) {
        return gals * pricePerGallon;
    }
}

public class CarV7Tester {

    public static void main(String[] args) {

        String carType1, carType2, carType3;
        int sMiles1, sMiles2, sMiles3;
        int eMiles1, eMiles2, eMiles3;
        double gals1, gals2, gals3;
        double pricePerGallon1, pricePerGallon2, pricePerGallon3;
        int distance1, distance2, distance3;
        double cost1, cost2, cost3;
        double mpg1, mpg2, mpg3;
        double gpm1, gpm2, gpm3;

        carType1 = "06 Saturn View";
        carType2 = "03 Toyota Camr";
        carType3 = "10 Nissan Leaf";
        sMiles1 = 5678;
        sMiles2 = 5678;
        sMiles3 = 5678;
        eMiles1 = 6015;
        eMiles2 = 6015;
        eMiles3 = 6015;
        gals1 = 15.8;
        gals2 = 17.6;
        gals3 = 14.9;
        pricePerGallon1 = 2.67;
        pricePerGallon2 = 2.8;
        pricePerGallon3 = 2.58;

        CarV7 car1 = new CarV7(carType1, eMiles1, sMiles1, gals1, pricePerGallon1);
        CarV7 car2 = new CarV7(carType2, eMiles2, sMiles2, gals2, pricePerGallon2);
        CarV7 car3 = new CarV7(carType3, eMiles3, sMiles3, gals3, pricePerGallon3);

        distance1 = car1.calcDistance(eMiles1, sMiles1);
        distance2 = car2.calcDistance(eMiles2, sMiles2);
        distance3 = car3.calcDistance(eMiles3, sMiles3);

        cost1 = car1.totalCost(pricePerGallon1, gals1);
        cost2 = car2.totalCost(pricePerGallon2, gals2);
        cost3 = car3.totalCost(pricePerGallon3, gals3);

        mpg1 = car1.calcMPG(distance1, gals1);
        mpg2 = car2.calcMPG(distance2, gals2);
        mpg3 = car3.calcMPG(distance3, gals3);

        gpm1 = car1.calcGPM(gals1, distance1);
        gpm2 = car2.calcGPM(gals2, distance2);
        gpm3 = car3.calcGPM(gals3, distance3);

        System.out.printf("%40s", "Gas Mileage Calculations");
        System.out.println();
        System.out.printf("%-13s %12s %10s %10s %10s %8s %6s %10s %10s", "Type of Car", "Start Miles", "End     Miles", "Distance", "Gallons", "Price", "Cost", "Miles/Gal", "Gal/Mile");
        System.out.println();
        System.out.println("=================================================================================================");
        System.out.printf("%-14s %9d %10d %10d %9.1f %8.1f %8.1f %10.3f %9.3f\n", carType1, sMiles1, eMiles1, distance1, gals1, pricePerGallon1, cost1, mpg1, gpm1);
        System.out.printf("%-14s %9d %10d %10d %9.1f %8.1f %8.1f %10.3f %9.3f\n", carType2, sMiles2, eMiles2, distance2, gals2, pricePerGallon2, cost2, mpg2, gpm2);
        System.out.printf("%-14s %9d %10d %10d %9.1f %8.1f %8.1f %10.3f %9.3f\n", carType3, sMiles3, eMiles3, distance3, gals3, pricePerGallon3, cost3, mpg3, gpm3);
    }
}

Answer 1

如果查看CarV7文件，您将拥有大量未在类中使用的实例变量。看起来你没有使用你在构造函数中设置的任何东西。

Answer 2

将私有实例变量的声明更改为：

private String myCarType1;
private int mySmiles1;
private int myEmiles1;
private double myGals1;
private double myPricePerGallon1;

...因为根本没有使用其他变量。

然后按如下方式更改构造函数：

CarV7 (String carType, int eMiles, int sMiles, double gals, double pricePerGallon)
{
  myCarType1 = carType;
  mySmiles1 = sMiles;
  myEmiles1 = eMiles;
  myGals1 = gals;
  myPricePerGallon1 = pricePerGallon; 
} 

不要在主方法中更改局部变量的名称。

Finally run the code... it should work.

Answer 3

为什么你需要实例变量？似乎没有一个成员方法使用实例变量。因此，这些方法可以定义为静态，您甚至不需要首先实例化该类。

Answer 4

我给你的CarV7类一些实例变量。由于变量是在构造函数中设置的，因此这些方法不需要任何参数。

package com.ggl.car;

public class CarV7 {

    private int eMiles;
    private int sMiles;

    private double gallons;
    private double pricePerGallon;

    private String carType;

    public CarV7(String carType, int sMiles, int eMiles, 
            double gallons, double pricePerGallon) {
        this.carType = carType;
        this.sMiles = sMiles;
        this.eMiles = eMiles;
        this.gallons = gallons;
        this.pricePerGallon = pricePerGallon;
    }

    public int calcDistance() {
        return eMiles - sMiles;
    }

    public double calcMPG() {
        return (double) calcDistance() / gallons;
    }

    public double calcGPM() {
        return gallons / calcDistance();
    }

    public double totalCost() {
        return gallons * pricePerGallon;
    }

    public int geteMiles() {
        return eMiles;
    }

    public int getsMiles() {
        return sMiles;
    }

    public double getGallons() {
        return gallons;
    }

    public double getPricePerGallon() {
        return pricePerGallon;
    }

    public String getCarType() {
        return carType;
    }

}

我的测试人员课程没有太大变化。我在main方法的开头摆脱了变量类型，并设置变量类型，因为我使用了每个变量。

package com.ggl.car;

public class CarV7Tester {

    public static void main(String[] args) {

        String carType1 = "06 Saturn View";
        String carType2 = "03 Toyota Camr";
        String carType3 = "10 Nissan Leaf";
        int sMiles1 = 5678;
        int sMiles2 = 5678;
        int sMiles3 = 5678;
        int eMiles1 = 6015;
        int eMiles2 = 6015;
        int eMiles3 = 6015;
        double gals1 = 15.8;
        double gals2 = 17.6;
        double gals3 = 14.9;
        double pricePerGallon1 = 2.67;
        double pricePerGallon2 = 2.8;
        double pricePerGallon3 = 2.58;

        CarV7 car1 = new CarV7(carType1, sMiles1, eMiles1, gals1, pricePerGallon1);
        CarV7 car2 = new CarV7(carType2, sMiles2, eMiles2, gals2, pricePerGallon2);
        CarV7 car3 = new CarV7(carType3, sMiles3, eMiles3, gals3, pricePerGallon3);

        int distance1 = car1.calcDistance();
        int distance2 = car2.calcDistance();
        int distance3 = car3.calcDistance();

        double cost1 = car1.totalCost();
        double cost2 = car2.totalCost();
        double cost3 = car3.totalCost();

        double mpg1 = car1.calcMPG();
        double mpg2 = car2.calcMPG();
        double mpg3 = car3.calcMPG();

        double gpm1 = car1.calcGPM();
        double gpm2 = car2.calcGPM();
        double gpm3 = car3.calcGPM();

        System.out.printf("%40s", "Gas Mileage Calculations");
        System.out.println();
        System.out.printf("%-13s %12s %10s %10s %10s %8s %6s %10s %10s", "Type of Car", "Start Miles", "End     Miles", "Distance", "Gallons", "Price", "Cost", "Miles/Gal", "Gal/Mile");
        System.out.println();
        System.out.println("=================================================================================================");
        System.out.printf("%-14s %9d %10d %10d %9.1f %8.2f %8.2f %10.3f %9.3f\n", car1.getCarType(), sMiles1, eMiles1, distance1, gals1, pricePerGallon1, cost1, mpg1, gpm1);
        System.out.printf("%-14s %9d %10d %10d %9.1f %8.2f %8.2f %10.3f %9.3f\n", car2.getCarType(), sMiles2, eMiles2, distance2, gals2, pricePerGallon2, cost2, mpg2, gpm2);
        System.out.printf("%-14s %9d %10d %10d %9.1f %8.2f %8.2f %10.3f %9.3f\n", car3.getCarType(), sMiles3, eMiles3, distance3, gals3, pricePerGallon3, cost3, mpg3, gpm3);
    }
}