无法从静态上下文引用java非静态变量x

Question

原谅我的无知。我是初学者：

为什么下面的代码给了我下面的编译错误？ [line:16]无法从静态上下文引用非静态变量x

public class average{
int [] numbers = {2,3,4,5,6};
double x = averageMark(numbers);

public static double averageMark(int [] numbers){
    int sum = 0;  
    double average = 0.000;
    for (int i = 0; i < numbers.length; i++){  
      sum = numbers [i] + sum;  
      average = sum/numbers.length;  
    }
    return average;
  }

  public static void main (String [] args){
  System.out.println(x);
  }
}

Answer 1

错误说明了一切

non-static variable x cannot be referenced from a static context

您必须使其成为x静态变量

static double x = averageMark(numbers);

或者创建一个Average实例并访问它

 public static void main (String [] args){
   System.out.println(new Average().x);
  }

顺便说一句，这是一个惯例，你的类名应该以大写字母开头

正如@mgaert所指出的，您还需要使数字数组成为静态的，因为您在静态方法中使用它

static int [] numbers = {2,3,4,5,6};

Answer 2

静态方法或变量不附加到特定对象，而是作为一个整体附加到类。它们是在类加载时分配的。如果您试图从静态方法内部使用实例变量，编译器会认为，“我不知道您在谈论哪个对象的实例变量！” 但是，如果您要创建average类的新实例，则可以通过此实例访问它，因此请按如下方式修改它：

public class average{
public int [] numbers = {2,3,4,5,6};
public double x;   
public static double averageMark(int [] numbers){
    int sum = 0;  
    double average = 0.000;
    for (int i = 0; i < numbers.length; i++){  
      sum = numbers [i] + sum;  
      average = sum/numbers.length;  
    }
    return average;
  }

  public static void main (String [] args){
  average a = new average(); // creating new instance 'a'
  a.x = average.averageMark(a.numbers); // assigning to variable 'x' of instance 'a' result of averageMark
  System.out.println(a.x); // output a
  }
}