Putting it all together

[Mike Van]

There was a Maryland programmer,
Who read the cert book until slumber,
Then after bit,
To show he got-it,
He wrote his own class modifier.

The classes were simple and frugal,
More code would not have been fruitful,
His job was to illustrate,
Not to obfuscate,
Small class sizes were much more useful.

He put in just enough print statements,
Not too many too few or too less,
But when it did run,
His brain from skull sprung,
Cuz his code was acting teh stoopids!

So he bought cheap beer and did drink it,
On his harsh code he thought "aww screw it",
But after much puking,
He submitted it thinking,
Perhaps Javaranch will help decipher it.


Here's the code:
class BaseClass{

private String name;

void setName(String name) {
this.name = name;
}

String getName() {
return this.name;
}

BaseClass() {
System.out.println("Base constructor called on the sly");

}

BaseClass(String name) {
System.out.println("Base constructor directly called");
setName(name);

}

void describe(Integer j) {
System.out.println("BaseClass" + getName() + " " + j);
}
}

class ChildClass1 extends BaseClass{

ChildClass1(String s){
System.out.println("ChildClass1 constructor called");
setName(s);
}

void describe(Integer j) {
System.out.println("ChildClass1" + getName() + " " + j);
}
}

class ChildClass2 extends BaseClass{

ChildClass2(String s){
System.out.println("ChildClass2 constructor called");
setName(s);
}


void describe(Integer j) {
System.out.println("ChildClass2" + getName() + " " + j);
}
}

public class TestFor {

public static void main(String... args){

BaseClass[] bcArray = { new BaseClass("One"), new ChildClass1("Two"), new ChildClass2("Three") };

int j = 0;

for(BaseClass b : bcArray) {
if( b instanceof BaseClass)
b.describe(j);

if( b instanceof ChildClass1 )
b.describe(j);

if(b instanceof ChildClass2 )
b.describe(j);
j++;
}
}
}

And here's the output:
Base constructor directly called
Base constructor called on the sly
ChildClass1 constructor called
Base constructor called on the sly
ChildClass2 constructor called
BaseClassOne 0
ChildClass1Two 1
ChildClass1Two 1
ChildClass2Three 2
ChildClass2Three 2

Can anyone help expaly why the Base constructor isn't called after ChildClass2 is initialized?

[J Sato]

I think I might know
But maybe I am just dumb
It is called before

That was my first attempt at haiku.
[ April 14, 2006: Message edited by: J Sato ]

[Henry Wong]

Can anyone help expaly why the Base constructor isn't called after ChildClass2 is initialized?

Because the BaseClass constructor is supposed to be called before the ChildClass2 constructor.

Henry

[Mike Van]

Originally posted by Henry Wong:


Because the BaseClass constructor is supposed to be called before the ChildClass2 constructor.

Henry

Henry,

I challenge you to show that is the reason. What you suggest is that if you have two subclasses with the same parent, you would not call the the parent constructor when each of the subclasses is create... that you would only call it once. Can you show that this is in fact what is happening?

<Later I added>

Doh! I see what you're saying. The missing call is the call to the base-class' argument-less constructor. Thanks Anyway!

</Later I added>

v/r,
[ April 14, 2006: Message edited by: Mike Van ]

[Bert Bates]

great poems!

[J Sato]

Mike,

This is my understanding. If the original question was why doesn't "Base constructor called on the sly" appear in the output after "ChildClass2 constructor called" it is because it appears before it.

------- BaseClass("One") -------
Base constructor directly called
--------------------------------

------- ChildClass1("Two") -----
Base constructor called on the sly
ChildClass1 constructor called
--------------------------------

------- ChildClass2("Three") ---
Base constructor called on the sly
ChildClass2 constructor called
--------------------------------

There is an implicit call to super() in the first line of the constructor for ChildClass2. HTH

[Mike Van]

Originally posted by Bert Bates:
great poems!

public class ThanksPrinter{

private String thanksMessage;

public void setThanksMessage(String thanksMessage) {
this.thanksMessage = thanksMessage;
}

ThanksPrinter() {
setThanksMessage("Thanks!");
}

ThanksPrinter(String msg) {
setThanksMessage(msg);
}

public void printThanksMessage() {
System.out.println(this.thanksMessage);
}

public static void main(String... args) {
String[] thanksMessages = {"Thanks Bert", "Nice book, by the way",
"It causes consternation, constipation,",
"and finally... Certification!"};
ThanksPrinter theThanksPrinter = new ThanksPrinter();
for(String s : thanksMessages) {
theThanksPrinter.setThanksMessage(s);
theThanksPrinter.printThanksMessage();
}
}
}

java -classpath . ThanksPrinter

lather, rinse, repeat

[Bert Bates]

constipation ?

[Mike Van]

Originally posted by Bert Bates:
constipation ?

Certification study,
Sitting long hours no rest,
Forgot bio-breaks.