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Java Forum / General / May 2006Constructor execution
Hi In the following code fragment: class Cups { static int cupCount = 10; Cups () { System.out.println ("Cups"); // Would like to create a array of cup objects here } } public class Cuppas2 { public static void main (String[] args) { System.out.println("Inside main"); System.out.println("Cup Count is " + Cups.cupCount); } } The constructor for class Cups does not get executed when the static field Cups.cupCount is referenced in the main method print statement. If in the initialization of the class Cups, I wanted to use a non simple code fragment e.g. creating an array of objects with a for loop, is there a way to do that in the client code without calling new Cuppas2()? Thanks Bob bagarow@yahoo.com wrote On 05/25/06 16:45,: > Hi > [quoted text clipped - 5 lines] > System.out.println ("Cups"); > // Would like to create a array of cup objects here Go right ahead; nothing's stopping you. > } > } [quoted text clipped - 8 lines] > The constructor for class Cups does not get executed when the static > field Cups.cupCount is referenced in the main method print statement. No, of course not. The job of a Cups constructor is to initialize a newly-created Cups object. You never ask for any Cups objects to be created, so no Cups constructor ever executes, or ever has any reason to execute. > If in the initialization of the class Cups, I wanted to use a non > simple code fragment e.g. creating an array of objects with a for loop, > is there a way to do that in the client code without calling new > Cuppas2()? Creating a new Cuppas2 object won't do anything about Cups. The Cuppas2 constructor (yes, there is one, even though you can't see it) calls the no-argument constructor of its superclass (Object, in this case) and then performs any Cuppas2-specific initialization. Since there isn't any Cuppas2-specific initialization to perform, the constructor just returns after the Object constructor returns to it. At no point does this do anything about the completely unrelated class Cups: it doesn't make any new Cups objects, and in fact it doesn't even cause the Cups class itself to be loaded. Perhaps (*perhaps*) what you're struggling toward is the static initialization block, something like class Cups { static int cupCount = 10; static Cups[] cups = new Cups[cupCount]; static { for (int i = 0; i < cups.length; ++i) cups[i] = new Cups(); } Cups() { ... as before ... } } ... but I confess I'm not at all clear as to your intent.  SignatureEric.Sosman@sun.com > bagarow@yahoo.com wrote On 05/25/06 16:45,: > > Hi [quoted text clipped - 64 lines] > -- > Eric.Sosman@sun.com I had a typo in my original email. Instead of saying new Cuppas2(), I should have said I wanted the initialization of class Cups to create a pool of Cup objects without having to call new Cups() in the client code but instead by the invocation of the Cups class via referencing the static field Cups.cupCount . So the static block you all have suggested in Cups does the trick. Thanks much Bob > bagarow@yahoo.com wrote On 05/25/06 16:45,: > > Hi [quoted text clipped - 64 lines] > -- > Eric.Sosman@sun.com I had a typo in my original email. Instead of saying new Cuppas2(), I should have said I wanted the initialization of class Cups to create a pool of Cup objects without having to call new Cups() in the client code but instead by the invocation of the Cups class via referencing the static field Cups.cupCount . So the static block you all have suggested in Cups does the trick. Thanks much Bob > static Cups[] cups = new Cups[cupCount]; > static { > for (int i = 0; i < cups.length; ++i) > cups[i] = new Cups(); > } IIRC, Effective Java suggests doing something like: static Cups[] cups = createCups(); private static Cups[] createCups() { Cups[] cups = new Cups[cupCount]; for (int i=0; i<cups.length; ++i) { cups[i] = new Cups(); } return cups; } I prefer the former, but at least be aware of the possibility of the latter. Tom Hawtin SignatureUnemployed English Java programmer http://jroller.com/page/tackline/ bagarow@yahoo.com ha escrito: > Hi > [quoted text clipped - 25 lines] > Thanks > Bob Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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