What's the difference between calling Double.valueOf(String s) and new Double(String s)?

Question

So I've got a String and I want to create a Double object with the String as a value.

I can call

Double myDouble = new Double (myString);

or I can call

Double myDouble = Double.valueOf(myString);

Is there a difference? I'm guessing the first guarantees a new object is created on the heap and the second might re-use an existing object.

For extra credit: the string might be null, in which case I want the Double to be null, but both the above throw a NullPointerException. Is there a way of writing

Double myDouble = myString == null ? null : Double.valueOf(myString);

in less code?

Answer 1

Depends on the implementation. openJDK 6 b14 uses this implementation of Double(String s):

this(valueOf(s).doubleValue());

So it calls valueOf(String s) internally and must be less efficient compared to calling that method directly.