Java - 使用 class 实例引用 static 方法

Question

What will exactly happen when using static method using that class instance? in build level and run time.

Thanks in advance.

Update: There are two classes, class one has a method, and the second one uses that method and after some time that method got changed to static. while running, I get IncompatibleClassChangeError.

Answer 1

If you call a static method from a class instance, it is identical to calling it in the standard static fashion (ie from the class name.) The compiler is smart enough to know to make the static call.

Answer 2

If you mean something like

class Foo {
  static void bar() { ... }
}

public class Baz {
  public static void main(String... argv) {
    new Foo().bar();  // Use static method here via instance
  }
}

then the instance is just completely ignored.

If you do it via reflection then it is also ignored.

If the underlying method is static, then the specified obj argument is ignored. It may be null.

Answer 3

Consider this scenario...

Class XYZ{

public static void functionTest(){
 // Your code
}

public static void main(String args[]){
XYZ x = new XYZ();
//Here we can execute the method functionTest() in 2 ways.
x.functionTest();
XYZ.functionTest();
}
}

Every class will have something called Context of a class , which means all the static methods and static variables get memory allocated in RAM without creating an object of that class and we call that memory as Context of a class.

And a reference(x) contains two parts, one is the actual address of the object(instance) and other is the address of context of the class.

When we call x.function() in above scenario, first it always searches for the context of the class, if it finds the method there it will execute it, if not found it will execute it from the instance of the class.

So, in whatever way you try to execute a static method, it will always be executed from the context of the class and not from the instance of the class.

That is the reason why static members of a class can be called in both ways.

and by calling the method from the instance, we are unnecessary creating the object which is not at all required ( unnecessary allocation of memory)