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

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.