Using try catch constructor chain java

Question

I have a class constructor and I need to perform a clone. From what I've read the best choice is to use a copy constructor, just like in C++. However, I've got an issue. If my "regular" constructor throws exceptions and such exceptions aren't even possible in a "copy constructor" how to I implement a try-catch if the first statement must be this.

public class X
{
   public X() throws MyException
   {
   }

   public X(final X original)
   {
      try {
         this();
      } catch (MyException e)
      {
      }
   }
}

Is the only option add throws MyException to copy constructor?

if you call this() you just init a new empty object. if you want a real copy with all values you should add a null-checking to x(final X original) and then copy each field from original to this.<field> — LenglBoy
– LenglBoy, Commented Oct 12, 2017 at 10:56
"If my "regular" constructor throws exceptions and such exceptions aren't even possible in a "copy constructor"" Even if you don't see a way, if a throws is present, assume you need to managed it or rethrow the exception. Don't assume an exception defined in a method declaration can't happen. If I need to update your class and I see the exception was defined, I know that this was expected so I can't throw that exception in my updated version without having to worry. The contract was already signed. — AxelH
– AxelH, Commented Oct 12, 2017 at 10:58
Possible duplicate of Java call constructor from constructor — vichu
– vichu, Commented Oct 12, 2017 at 11:14

LenglBoy · Accepted Answer · 2017-10-12 11:02:39Z

0

Copy all data to a new instance by constructor could look like this:

public class X
{
   // some Fields....
   int a, b, c;

   public X() { }

   public X(final X originalX) throws InvalidArgumentException
   {
      if(originalX == null) {
        throw new InvalidArgumentException("originalX should not be null!");
      }
      this.a = originalX.getA();
      //...
   }
   // getter-setter....
}

And it´s called like this in main() or where ever else:

// x_1 is filles with Data...
X x_2;
try {
    x_2 = new X(x_1);
} catch(InvalidArgumentException ex) {
    LOG.reportError(ex.getMessage());
    x_2 = new X();  // prevent NullPointer for usage afterwards
}

answered Oct 12, 2017 at 11:02

LenglBoy

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3 Comments

AxelH Over a year ago

true, but the question is about "catching the exception from this()"

LenglBoy Over a year ago

but calling this() is doing nothing and shouldn´t be required for his usage.

AxelH Over a year ago

Maybe, but this is what your answer should explain ;) What if the constructor have a init() statement, what can he do ?

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