how to know if the object is updated ?

[ilias basha]

Can anybody explain me how to know if any java object gets updated/re-loaded.

Consider if i have java object which will be loaded only if it meets certain conditions. and i need to check if that object is actually updated or not.

[Hunter McMillen]

You can use print statements to determine the value of an object at a specific point in time.

Ex:

Student newStudent = new Student();

//returns true if the student is in this course
if(newStudent.isInThisCourse())
{
     //set the student attributes
    //gpa, name, student id
}

System.out.println(newStudent.toString());

in this case if newStudent didn't meet the condition all of the student fields(i.e. gpa, name, student id) would be empty.

-Hunter

[David Newton]

@Hunter: what?

@Ilias: Loaded from where? In any case, one of the easiest ways to detect changes would be to compute a hash code, store it, and check against it later. This, of course, depends on having a good hash function, and may not always be appropriate. You could also instrument getters/setters to set a "modified" flag if their values actually cause a change--there are a number of ways this could be implemented.

I'm not sure how Hibernate determines dirtiness, but you could look into that and see what their implementation does.

[ilias basha]

David Newton wrote:
@Ilias: Loaded from where? In any case, one of the easiest ways to detect changes would be to compute a hash code, store it, and check against it later. This, of course, depends on having a good hash function, and may not always be appropriate. You could also instrument getters/setters to set a "modified" flag if their values actually cause a change--there are a number of ways this could be implemented.

I'm not sure how Hibernate determines dirtiness, but you could look into that and see what their implementation does.

I have written code that will load the property file, which will load only time stamp of previous instance differs with current one. I want to know if the object has got updated of the said class or not.

[Hunter McMillen]

My mistake, I thought the question was about the changing values of an object.

-Hunter