Why can other methods be “static” but a constructor cannot?

Question

I do not understand why the main method has to be static. I understand static variables but static methods are difficult for me to grasp. Do static method exists so that one

Answer 1

Constructors are neither entirely static (class level) or entirely non-static (instance level).

• Unlike instance methods, constructors are not inherited.
• Unlike static methods, a constructor can refer to this.

So, why can't you declare a constructor static?

Well, my take is that a (redundant) static keyword would be confusing and would not serve any purpose. Therefore they decided not to allow it.

---

The explanation that static initialization blocks can be viewed as constructors is (IMO) conceptually wrong. (It is analogous to saying that an instance initialization block is a regular constructor. Which is equally wrong.)

The key distinctions between static initialization and construction¹ are:

• static initialization happens at an indeterminate time²; there is no equivalent to new for class initialization,
• there is no straight-forward way to pass (constructor) parameters to the initialization code
• there is no practical way to recover from errors occurring during static initialization.

^{1 - Hypothetically, if class initialization was explicit, then it would make sense to have static constructors. But the downsize would be that applications would need to explicitly "construct" all of the classes that they used ... which would be horrible.}

^{2 - You have a degree of control if you load a class dynamically, but even then if the class has already been loaded and initialized in the current classloader, then attempting to control initialization will fail.}

---

I do not understand why the main method has to be static.

It has to be if you want the main method to act as an entrypoint for your application.

The problem is that if main was an instance method, then there would need top be an instance of your entrypoint class to call the main method on. But how do you create it? Which constructor would you choose? What if there was no public constructor?

The bottom line is that this is the way that Java was designed ... back in the 1990's ... and so far they have not seen the need to change this.

---