以单独的方法初始化 Java object：为什么这不起作用

Question

Here's a thing that I can't tell I'm surprised it won't work, but anyway it's interesting for me to find the explanation of this case. Imagine we have an object:

SomeClass someClass = null;

And a method that will take this object as a parameter to initialize it:

public void initialize(SomeClass someClass) {
  someClass = new SomeClass();
}

And then when we call:

initialize(someClass);
System.out.println("" + someClass);

It will print:

null

Thanks for your answers!

Answer 1

It's impossible to do in java. In C# you'd pass the parameter using the ref or out keyword. There are no such keywords in java. You can see this question for details: Can I pass parameters by reference in Java?

Incidentally, for that same reason you cannot write a swap function in java that would swap two integers.

Answer 2

As Armen mentioned, what you want to do is not possible this way. Why not use a factory method?

Answer 3

And a method that will take this object as a parameter to initialize it:

The method does not take an object as a parameter in your case. It takes a reference which points to null. Then it copies this reference and points it to a new instance of SomeClass . But obviously, the reference that you passed as a parameter still points to null .