What could go wrong with calling a static method with an object in Java?

Question

If I have the following:

class A {
  public A() { }
  public static void foo() { System.out.println("foo() called"); }
}

public class Main {
  public static void main(String [] args) {
    A a = new A();
    a.foo(); // <-- static call using an instance.
    A.foo(); // <-- static call using class
  }
}

Are there any problems that may arise from calling foo() using an instance? Does the JVM treat the first call to foo() exactly as a static method, or is there some technical subtlety?

Answer 1

The two calls are the same. The problem that comes to mind is when overriding class A, you cannot directly override foo().

Answer 2

Not 100% sure, but you may risk hitting a null pointer exception if your instance is null.

Answer 3

Its very easy to introduce subtle logic errors by calling static methods from instances. Case in point, this doesn't do what you think it does:

Thread t = new Thread(...);
t.sleep(1000);

sleep is a static method which pauses the currently executing thread, not the thread instance.

Answer 4

Its just considered bad form / practice. Avoid this.

Answer 5

One good reason is that you can confuse other people who might need to read or update your code. It really "seems" like the instantiated object should be involved in the method call, when in fact it isn't (and in fact it can be null). It's unnecessary obfuscation.