One constructor - multiple arguments

Question

I've found a task on some Java programming competition. One must create class Sentence with only one argument 'text' and only one constructor. Here's sample test code :

 Sentence s1=new Sentence("only","CAT"),
      s2=new Sentence("and", 2, "mice"),
      s3=new Sentence(s1,s2,"completely","alone"),
      s4=new Sentence(s3, "on the ", new Integer(32), "th street");

 System.out.println(s1); Only cat.
 System.out.println(s2); Only cat and 2 mice.
 System.out.println(s3); Only cat and 2 mice completely alone.
 System.out.println(s4); Only cat and 2 mice completely alone on the 32th street.

How one contructor can serve different sets of arguments ? Is there something like dynamical constructor which recognizes sent values?

BalusC · Accepted Answer · 2010-03-03 17:35:51Z

7

Make use of varargs.

public class Sentence {

    public Sentence(Object... text) {
        // ...
    }

}

Fill in the constructor logic yourself. It may however become a bit awful to determine all the types. You could make use of Object#toString() and let the Sentence class implement one as well.

edited Mar 3, 2010 at 17:35

answered Mar 3, 2010 at 17:22

BalusC

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1 Comment

sasklacz Over a year ago

I guess the types are only those supported within test code. Dunno, haven't competed in this competition :)

Bozho · Accepted Answer · 2010-03-03 19:33:26Z

2

Yes, java 5+ support varargs - you can pass mulitple arguments of the same type, like this:

public Constructor(Object... args){..}
public void methodName(Object... args){..}

Then the arguments are accessible as an array of Object. But that's not always a good practice. Varargs should be used only for arguments with the same logical type. For example, a list of names. If multiple arguments should be passed I'd suggest to overload constructors.

In this case the arguments are all of the same logical type - "word", so this is a nice way to do it.

edited Mar 3, 2010 at 19:33

answered Mar 3, 2010 at 17:22

Bozho

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1 Comment

Cornelius Dol Over a year ago

Well... the various printf methods use varargs with different argument type. I disagree with the "not good practice" remark.

Jay · Accepted Answer · 2010-03-03 17:39:02Z

1

If you accept Object... value, then you can convert anything to a string with toString. toString is defined on Object so every Object should support it.

answered Mar 3, 2010 at 17:39

Jay

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3 Comments

Cornelius Dol Over a year ago

Although, not every object will provide an implementation which is practically useful to this Sentence object.

Jay Over a year ago

@Monkey: Well, sure, but what would you do then? If this was a real program, I would think it would be the programmer's responsibility to only call it with values that give meaningful output. The alternative would be for the Sentence class to have a hard-coded list of what classes it will accept, which would be an awfully limiting design decision.

Jay Over a year ago

Further thought: You could, of course, create an Interface with a toSentenceString function or something of the sort, and then only accept inputs of type Interface. That would allow you to control what gets passed in without having to pre-determine the list. But then you couldn't pass in a String or an Integer without wrapping it in something that implemented the interface. Sounds to me like it would be way more trouble than it was worth.

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