Overloaded constructors, final and assert

Question

I am having some difficulties of using final variables and still have the ability to check parameters in the constructor.
For example take this class:
class MyObject {
final String id;
final String value;
public MyObject(String id, String value) {
assert id != null : "error";
assert value != null : "error";
this.id = value;
this.value = value;
public MyObject(Wrapper wrapper) {
assert wrapper != null : "error";
this(wrapper.getId(), wrapper.getValue());
The above code won't compile because the assert is not allowed before the call to the other constructor.
I cannot do the initializing of variables in a normal method, because I cannot assign to the variables at that point.
I can use a static method that created to object, but is that really a good idea?
Any suggestions?

Answer 1

Generally, assert in parameters of public methods is not recommended.
Assertion is for situations that are even more exceptional than Exceptions,
for example, to detect bugs in the code.
Theoretically, in public methods you don�t have to use assert to verify if the
parameter is null or not null. You have to use if statement and throw
NullPointerException,for example. If the method were private, like your
init( ) method, so that�s ok and you could use assertion.It does not make sense to me why I would use asserts in private methods
and not for public ones. Especially since the same parameters might
end up in a private method anyway.
For me asserts are about pre-conditions, post-conditions and constraints.
I especially find them useful for pre-conditions and making very clear
to the caller what I expect of him.
A good article about assert can be found at javaworld
http://www.javaworld.com/javaworld/jw-12-2001/jw-1214-assert.html
Anyway, it's kinda off-topic, because if I would use an if statement
and throw an exception, I have the exact same problem!
This does not compile:
public MyObject(Wrapper wrapper) {
    if (wrapper != null)
        throw NullPointerException("error");
    this(wrapper.getId(), wrapper.getValue());
}