Static method Causes problem

Question

Dear all,

I have a static method as following:

public static void writeArticle(TypeA typeA, TypeB typeB) {
  AWriter writer =  AFactory.getWriter("aWriter");
  Article article = writer.newArticle();

  /* PARAMETER WRITE START */

  article.set("title", typeA.getTitle());
  article.set("author", typeB.getName());
  article.set("age", typeB.getAge());
  // …
  /* more set statments here */
  writer.write(article);
}

Could this method cause a problem that the writer will write a value-mixed Article? That is, when 2 class (Class A and ClassB) instances calling this method, will Article get some of typeA values from ClassA and some from ClassB?

Answer 1

No. Why do you think the arguments from two different calls would get mixed up? There's no reason to think they would.

If this is a multi-threaded program, you should ofcourse be careful with sharing objects between threads; if those objects have mutable state (member variables that can be changed) you should take care that two threads are not modifying the state at the same time.

Answer 2

Whenever you say static, you do not talk about instance method calls. Always static methods should be called with their class name.

The static method is totally isolated at instance level. Even though it might write a value-mixed, it is what you want it to write isnt it?

Answer 3

No. It would be hell otherwise.

Answer 4

This would only be the case if both calls accessed and changed common state, e.g. assuming the class in which this method is defined is called ArticleWriter, they would both read and change static fields of ArticleWriter.

Answer 5

That would be impossible for your code. typeA has method getTitle and typeB has method getName. Which fields are getting mixed up?

Answer 6

It's unknowable from this code snippet. The first question to address is whether or not this method may be called from two different threads at the same time. If so the problem is most likely that two threads are modifying the same object at the same time (either article or writer). The easiest way to address that would be to synchronize writeArticle().

Answer 7

No, method parameters and local variables are thread-safe as long as they do not refer to shared objects.