我写了这样的测试代码:

class MyProgram
{
    int count = 0;
    public static void main(String[] args)
    {
        System.out.println(count);
    }
}

但它给出了以下错误:

Main.java:6: error: non-static variable count cannot be referenced from a static context
        System.out.println(count);
                           ^

我如何让我的方法识别我的类变量?


当前回答

这是因为您不创建模型类的实例,您必须在每次使用非静态方法或变量时创建实例。

你可以很容易地修复这个,看看下面的图片

没有创建类的实例

我的模型类文件

通过创建实例,然后使用类的非静态方法或变量,很容易出错

其他回答

静态字段和方法连接到类本身,而不是它的实例。如果你有一个类a,一个“正常”(通常称为实例)方法b和一个静态方法c,并且你为你的类a创建了一个实例a,那么对A.c()和a.b()的调用是有效的。方法c()不知道连接的是哪个实例,因此它不能使用非静态字段。

解决方案是要么使字段静态,要么使方法非静态。你的主要内容可以是这样的:

class Programm {

    public static void main(String[] args) {
        Programm programm = new Programm();
        programm.start();
    }

    public void start() {
        // can now access non-static fields
    }
}

这是因为您不创建模型类的实例,您必须在每次使用非静态方法或变量时创建实例。

你可以很容易地修复这个,看看下面的图片

没有创建类的实例

我的模型类文件

通过创建实例,然后使用类的非静态方法或变量,很容易出错

为了能够从静态方法中访问它们,它们需要是静态成员变量,如下所示:

public class MyProgram7 {
  static Scanner scan = new Scanner(System.in);
  static int compareCount = 0;
  static int low = 0;
  static int high = 0;
  static int mid = 0;  
  static int key = 0;  
  static Scanner temp;  
  static int[]list;  
  static String menu, outputString;  
  static int option = 1;  
  static boolean found = false;

  public static void main (String[]args) throws IOException {
  ...

The first thing is to know the difference between an instance of a class, and the class itself. A class models certain properties, and the behaviour of the whole in the context of those properties. An instance will define specific values for those properties. Anything bound to the static keyword is available in the context of the class rather than in the context of an instance of the class As a corollary to the above variables within a method can not be static static fields, and methods must be invoked using the class-name e.g. MyProgram7.main(...) The lifetime of a static field/method is equivalent to the lifetime of your application

如。 例如,汽车具有属性颜色,并表现出行为“运动”。 以25公里每小时的速度行驶的红色大众甲壳虫为例。

现在,汽车的静态属性将是道路上的车轮数量(4),这将适用于所有汽车。

HTH

I will try to explain the static thing to you. First of all static variables do not belong to any particular instance of the class. They are recognized with the name of the class. Static methods again do not belong again to any particular instance. They can access only static variables. Imagine you call MyClass.myMethod() and myMethod is a static method. If you use non-static variables inside the method, how the hell on earth would it know which variables to use? That's why you can use from static methods only static variables. I repeat again they do NOT belong to any particular instance.