Java 多实例can';t使用相同的变量,变量不变
我不太确定这有什么问题,我确信这与范围有关。昨天我遇到了一个问题,由于我多次调用该方法,一个字段将自身初始化回零,使得一个类字段修复了这个问题,因为它保留了它的值,而不管调用任何方法多少次 现在我遇到了相反的问题,我需要重置字段,因为另一个对象需要使用它(这可能/不好的做法吗?) 代码如下:Java 多实例can';t使用相同的变量,变量不变,java,Java,我不太确定这有什么问题,我确信这与范围有关。昨天我遇到了一个问题,由于我多次调用该方法,一个字段将自身初始化回零,使得一个类字段修复了这个问题,因为它保留了它的值,而不管调用任何方法多少次 现在我遇到了相反的问题,我需要重置字段,因为另一个对象需要使用它(这可能/不好的做法吗?) 代码如下: public class TestDigitalCamera { static String brand; static double megaPixels; static dou
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");
}
}
这是因为范围吗?该变量可用于任何和所有对象,但只能用于1?最好的方法是什么 您有以下代码:
camera = getInformation(camera);
displayInfo();
camera2 = getInformation(camera2);
displayInfo();
在这里,您的方法displayInfo()
实际上并没有在调用它的时候从camera
对象获取任何参数和打印信息。即使您在第二次调用getInformation
时获得了对camera2
对象的引用,但实际上并没有打印它
您可以这样声明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");
}
您应该像这样重构代码:
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");
}
然后在main
方法中:
public static void main(String[] args) {
camera = getInformation(camera);
displayInfo(camera);
camera2 = getInformation(camera2);
displayInfo(camera2);
}
如果在main
方法中声明两个DigitalCamera
实例,如下所示
DigitalCamera camera = getInformation(camera);
这样就不需要单独的静态变量
我强烈建议您阅读Java教程中关于类和实例成员的部分:我会这样编写您的类 公共类数码相机{
public static test_display(){
DigitalCamera camera = getCamera();
System.out.println("Brand: " + camera.getBrand() + "\n"
+ "Megapixels : " + camera.getMegaPixels() + "\n"
+ "Price : $" + camera.getPrice() + "\n");
}
public static getCamera(){
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
DigitalCamera dc = new DigitalCamera();
dc.setBrand(brand);
dc.setMegaPixels(megaPixels);
return dc;
}
public static void main(String[] args) {
test_displainfo();
}
}你知道displayInfo总是使用camera,所以它从不使用camera2吗?天哪…我感觉像是这样一个工具lol。在不复制代码的情况下,让displayInfo同时输出两者的最佳方法是什么?让displayInfo接受一个参数:displayInfo(数码相机)是的,我假设,感谢您清除了这个问题。您为什么不能将
displayInfo
作为DigitalCamera
类的实例方法?这样,您就可以简单地执行camera.displayInfo()
和camera2.displayInfo()
。有趣的是,您这样做的原因是什么?是不是这样,您可以随时调用该方法,并始终拥有新的摄影机对象?而不是创建xxx数量的实例?是的,只要您想创建新的摄影机对象,就可以调用此方法。而且您创建的实例变量属于camera对象,所以您不应该创建为TestCamera类的实例变量。如果你想让它变得更好,摆脱Scanner类,创建json/xml/properties文件,列出你想要显示和读取的相机属性,并为每个属性创建相机对象。我会读到的,我主要是从我的书中学习。事实上,这经常会让您阅读java文档,让您习惯于非常好地引用它。但是我想你的书提到的是Java API文档,而不是Java教程。看看我的代码,这看起来很愚蠢。我把变量名绑定到参数上,因为我使用的是setter,所以实际上什么都不做……我想我可以直接执行一个标准方法,请求用户输入来初始化变量