hashCode question

Enrique

Hi,
·
This is more a Java question.
·
When I compile the attached program I get the following error from the compiler: “Error: No method hashCode was found in testExt$extended”
·
My question is why? Why do I get error if supposedly extended should inherit hashCode from Object.

Peter Verkaik

Javelin java is not like pc java.
Object has no hashCode component.

regards peter

Enrique

But the Javelin Stamp User’s manual on page 112 states that there is a hashCode method.

Peter Verkaik

The file Object.java in folder ...\lib\java\lang
shows

· /**
·· * Returns a hash code for this object. This is useful for implementing
·· * hash tables and other data-structures requiring a random index. The
·· * hash code is unique for each object while a program is running.
·· *
·· * @return a unique hash code for this object.
·· */
· //public int hashCode() {
· //· /* ?? This should be implemented to return the pointer to this. */
· //· return 1;
· //}

so apparently hashCode() is not implemented.
You could implement it as
public Object hashCode() {
· return this;
}

but then hashCode is not of type int.

regards peter

Enrique

What's the type of this?


Enrique

Peter Verkaik

The type of this is Object.
Unfortunately you cannot use (int)this
but you can compare Objects to each other,
and create arrays of Object.

regards peter

Enrique

So basically this is a reference to Object. I want to have a way of identifying different instances of object of the same class so I can print debugging information on the terminal and know from whom it’s coming. Any idea how to do it?


Enrique

Peter Verkaik

You can create an arrray of Object

Object obj[noparse]/noparse = new Object[noparse][[/noparse]12];
You can store·Objects into this array

myType1 tp1 = new myType1();
myType2 tp2 = new myType2();
etc.

obj[noparse][[/noparse]0] = tp1;
obj[noparse][[/noparse]6] = tp2;
obj[noparse][[/noparse]3] = null; //empty entry

You can then use the index of·obj as a printable value.
As each object has·a unique address (represented by this),
as long as you only allow a specific object to be in obj[noparse]/noparse only once,
the index of obj[noparse]/noparse is also unique·to a specific object.
The index value can be printed or used as index·in an array (of Strings)
holding the names of the objects or whatever.

regards peter

Enrique

Thanks