Can constructor return a null object?

Question

While looking through some old code I came across this gem:

MyObject o = new MyObject("parameter");
if (o == null) o = new MyObject("fallback parameter");

The second line is marked in Eclipse as dead code, and I understand why. No exception seems to be explicitly thrown, and it isn't possible for the MyObject constructor to throw any kind of exception (such as NullPointerExceptions).

My question is why there is a null check? Was it previously possible in an old version of Java for a constructor to return null? Or is this simply useless and dead code?

Answer 1

It's simply dead code.

new MyObject("parameter") will not return null in any version of java.

Answer 2

This was simply usesless dead code. Once CTOR has executed successfully, you have reference to the object.

Answer 3

From section 15.9.4 of the JLS:

The value of a class instance creation expression is a reference to the newly created object of the specified class. Every time the expression is evaluated, a fresh object is created.

So no, it can never return null.

Answer 4

When you create a new Object(), you create an address in memory, and this address is not 'null', but your Object may be empty.

You have to test 'null' for Object transmitted by parameters.

Answer 5

My guess is that it was written by a C programmer who is used to testing the return value of malloc() for NULL, malloc() can return NULL if your system runs out of memory.

The code doesn't make sense in Java since Java will throw an OutOfMemoryError` if it runs out of memory.

Answer 6

The code is dead in any version of java. It's not possible for a constructor to return null and even if an exception would be thrown from the constructor, the next line won't be called.