Discovering a java object's construtor

Wimnat · 26 Apr 2007 at 21:57

I have a Java class with two constructors. One accepts a string and 2 vectors, the other accepts a string and a vector.

Code:

/* Constructor 1 */
public P(String[] pSL, Vector pHd) {
}

/* Constructor 2 */
public P(String[] pSL, Vector pHd, Vector pBd) {
}

My question is simply this. How can I tell what constructor has been used to create my object?

I need to know because I only want to call a certain function if the second constructor has been used.

Chrisss · 26 Apr 2007 at 22:01

You could try setting a boolean to true depending on which one is used, and then check that, I assume that'd work.

Dj_Jestar · 26 Apr 2007 at 22:21

then only call the method from within the second constructor :\

Wimnat · 26 Apr 2007 at 22:30

Dj_Jestar said:
then only call the method from within the second constructor :\

A little more explanation may be necessary...

Class Sniff sniffs a packet from the network and casts it as an object of type packet.

A method then analyses this packet and uses one of the two constructors to make an object based on the packet contents.

Sniff then calls a print function for the two or three parts of the object. If no third part has been created then obviously an error is thrown.

Thinking about it i could just catch the error and do nothing but is this good practice?

Una · 26 Apr 2007 at 22:46

If Vector pBd is assigned to a instance variable you could just check to see if pbB is not null if it is execute the code for that, else execute the other code.

You can have if statments in toString() methods you know.

Dfhaii · 27 Apr 2007 at 02:42

I was expecting some fun with reflection when I read the thread title.

As said before, set a boolean variable if the method can be run in the constructor and then check it before calling.

Welshy · 27 Apr 2007 at 02:47

You say a string is passed into the constructor, but I assume you know you have an array of strings in the parameter list?

Wimnat · 27 Apr 2007 at 09:45

Sorted now. Stupid question really now I think about it but I'd been coding all day yesterday and I guess I was just having one of those coders block moments!

Dfhaii said:
I was expecting some fun with reflection when I read the thread title.

What the hell is reflection!? Is it as exciting as it sounds?

Dj_Jestar · 27 Apr 2007 at 09:49

Reflection is a very powerful tool, but it only applies to a small number of circumstances.

Dfhaii · 27 Apr 2007 at 14:59

Wimnat said:
What the hell is reflection!? Is it as exciting as it sounds?

Reflection is an incredibly useful bit of kit for creating, modifying, and inspecting objects dynamically at run time.

Visage · 27 Apr 2007 at 20:19

Dfhaii said:
Reflection is an incredibly useful bit of kit for creating, modifying, and inspecting objects dynamically at run time.

Is it that useful?

Generally excessive use of reflection is a sign that your design is in some way flawed, IMO.

Dj_Jestar · 27 Apr 2007 at 21:21

Visage said:
Is it that useful?

Generally excessive use of reflection is a sign that your design is in some way flawed, IMO.

There are some designs where Reflection, and lots of it, are works of genius. Not everything is an a->b scenario, so you can't create a glorified script for it; which is all tightly controlled objects are - glorified scripts.