java - 多个实例不能使用同一个变量，变量不会改变

Question

我不太确定这有什么问题，我确信它与范围有关。昨天，我遇到了一个问题，由于我多次调用该方法，字段会将自身初始化回零，从而使类字段修复了此问题，因为无论调用任何方法多少次，它都保留其值。

现在我遇到了相反的问题，我需要重置该字段，因为另一个对象需要使用它(这可能/不好的做法吗？)

这是代码:

public class TestDigitalCamera {

    static String brand;
    static double megaPixels;
    static double price;

    //create 2 camera instances with the values of the variables tied to the arguments.
    static DigitalCamera camera = new DigitalCamera(brand, megaPixels);
    static DigitalCamera camera2 = new DigitalCamera(brand, megaPixels);


    public static void main(String[] args) {

        //no idea what this technique is called, need to look back but I know what it does
        //I could use a for loop and reuse the same object over and over(would that even work anyway?) but the task says
        //that i require 4 instances, ofc I am just working with 2 atm for simplicity
        camera = getInformation(camera);
        displayInfo();
        camera2 = getInformation(camera2);
        displayInfo();


    }

    //it basically runs this for the camera instance...right? lol
    public static DigitalCamera getInformation(DigitalCamera dc){
        Scanner userInput = new Scanner(System.in);

        //self explanatory
        System.out.println("Enter brand: ");
        brand = userInput.next();
        System.out.println("Enter Mega Pixels: ");
        megaPixels = userInput.nextDouble();

        //I have another class setup with getters/setters for this, which get used in the next method
        dc.setBrand(brand);
        dc.setMegaPixels(megaPixels);
        return dc;      

    }

    public static void displayInfo(){

        //users the getters to pull the values
        //the price is calculated using an if statement
        System.out.println("Brand: " + camera.getBrand() + "\n"
                + "Megapixels : " + camera.getMegaPixels() + "\n"
                        + "Price : $" + camera.getPrice() + "\n");
    }

}

这是由于范围的原因吗？该变量可用于任何和所有对象，但只能用于 1?解决这个问题的最佳方法是什么？

Answer 1

您有以下代码:

camera = getInformation(camera);
displayInfo();
camera2 = getInformation(camera2);
displayInfo();

这里，您的方法 displayInfo() 在调用时并没有真正从 camera 对象获取任何参数和打印信息。尽管您在第二次调用 getInformation 时获取了 camera2 对象的引用，但您并没有真正打印它。

您可以像这样声明displayInfo:

public static void displayInfo(DigitalCamera camera) {
    //users the getters to pull the values
    //the price is calculated using an if statement
    System.out.println("Brand: " + camera.getBrand() + "\n"
         + "Megapixels : " + camera.getMegaPixels() + "\n"
         + "Price : $" + camera.getPrice() + "\n");
}