Non-static variable cannot be referenced from a static context

In Java, a non-static (also known as an instance) variable or method can only be accessed from an instance of the class. A static (also known as a class) variable or method, on the other hand, can be accessed directly from the class, without the need for an instance.

If you try to access a non-static variable or method from a static context (such as from a static method or from the main method, which is always static), you will get a compilation error similar to "non-static variable cannot be referenced from a static context".

Here's an example of how this error can occur:

public class MyClass {
  private int x;  // non-static variable

  public static void main(String[] args) {
    System.out.println(x);  // error: non-static variable x cannot be referenced from a static context
  }
}

To fix this error, you can either make the variable or method static, or you can create an instance of the class and access the variable or method through the instance.

For example:

public class MyClass {
  private static int x;  // static variable

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

or

public class MyClass {
  private int x;  // non-static variable

  public static void main(String[] args) {
    MyClass instance = new MyClass();
    System.out.println(instance.x);  // okay
  }
}