从静态方法调用非静态方法

Question

谁能解释一下为什么静态方法调用非静态方法是非法的？

Answer 1

A non-static method is an instance method which acts upon a specific instance (object), and has access to that object's members. A static method is not associated with a specific instance.

It is legal to call a non-static method if you provide an instance:

class Foo
{
    public static void f()
    {
        instanceMethod(); // Not OK - no instance provided.
        this.instanceMethod(); // Not OK -  no "this" in static methods.
        new Foo().instanceMethod();  // OK because you provide an instance
    }

    public void instanceMethod() {}
}

Answer 2

because to call static method you don't need object of class, where to call non static method you need,

Static method is associated with class where non static method is associated with state (Object)

Answer 3

A non-static method is a method that executes in the context of an instance . Without an instance it makes no sense to call one, so the compiler prevents you from doing so - ie it's illegal.

If a method doesn't access any instance fields (aka instance variables) then it should probably be changed to be a static method.

Answer 4

非静态方法具有隐式参数this ，而静态方法则没有（因为没有this ），因此，不可能将非静态方法称为静态方法。

Answer 5

Static methods belong to the class. Non static methods belong to an instance.

The non static method require an instance ( this ) to be executed on. The static method don't require any instance, since the class itself is the instance to which it belongs.

If I have 100 object instance, every nonStatic() method invocation affects the state of a different object. So every nonStatic method is 'different' because it acts on different entities. At the same time, even if I have 100 instance of an object, calling staticMethod() doesn't affect any of those instances, because it can only affect the static members of the class.

There is 1 class and 1 instance of every static methods or static member variables.

For the non static members we have every single method associated to the class instance.

So if you would be able to call the nonStatic method, from a static method, which of the 100 instance would be affected? You see: it doesn't make sense.

Answer 6

Static methods are connected with the class. Regular methods are connected to the object.

In static method there is no object on which you can run the non-static method.

Answer 7

It is not illegal to call a non-static method from a static method. Whenever you invoke a static method there is no need of an instance of a class whereas in case of non-static case you do.