I lost the point: purpose of putting objects to null?

[Dado]

I lost the point:
What is purpose of putting objects to null:

If I make a class, JFrame for example, with button which start connection
dialog, which is class with connection and statement Object.
And every time I click the button first I put :
dialog = null
dialog = new dialog()

What is purpose to put dialog = null when all its objects are stay non-null?

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[Edwin Martin]

Dado wrote:

I lost the point:
What is purpose of putting objects to null:

If I make a class, JFrame for example, with button which start connection
dialog, which is class with connection and statement Object.
And every time I click the button first I put :
dialog = null
dialog = new dialog()

What is purpose to put dialog = null when all its objects are stay non-null?

There is no use in doing that.

Sometimes it's usefull to set a variable to null, to the memory it
occupies. But that's what you do after you have used the object, not before.

Edwin Martin.
--
http://www.bitstorm.org/

[AnonymousOne]

I personally use this to test if an object was ever set or not. If you
just check for (x == null) without actually SETTING x to null, then the
compiler would give you a "x may not be initialized" error.

Example:

java.sql.Connection c;

try {
c = java.sql.DriverManager.connect(...);
java.sql.Statement s = c.createStatement();
...
}
catch (Throwable thrown) {
// some code here
}
finally {
if (c == null) then c.close();
}

This example would not compile, because "c" is never initialized.
However, if we change the first line to:

java.sql.Connection c = null;

Then the finally block would work.
Dado wrote:

I lost the point:
What is purpose of putting objects to null:

If I make a class, JFrame for example, with button which start connection
dialog, which is class with connection and statement Object.
And every time I click the button first I put :
dialog = null
dialog = new dialog()

What is purpose to put dialog = null when all its objects are stay non-null?

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[Dan Nuttle]

You don't technically gain anything by doing this. However, I'm a believer
in declaring variables whenever possible at the top of a class or method.
Instead of having variable declarations scattered all over. So I tend to
have lots of lines like

MyObject _o = null;

at the top of a class or method. That way, when I see a variable and I
don't know what type it is, I can look at the top of the class or method and
quickly find out. You can just declare the variable without setting it to
null, but then your class might not compile unless every single method that
uses the variable makes sure it's been initialized.

Some coding philosophies consider it very bad form to declare and
instantiate a variable at the same time, in the body of a method, like this:

public void myMethod()
{

//Some code here
String myString = "ABC";

}

But this is more of a philosophy than a technology issue.
"Dado" <dz****@mail.inet.hr> wrote in message
news:ci**********@sunce.iskon.hr...

I lost the point:
What is purpose of putting objects to null:

If I make a class, JFrame for example, with button which start connection
dialog, which is class with connection and statement Object.
And every time I click the button first I put :
dialog = null
dialog = new dialog()

What is purpose to put dialog = null when all its objects are stay non-null?


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Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
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[EricF]

Actually you do gain something in a server or long running application by
setting objects to null. These objects can be garbage collected.

Eric

In article <62*****************@newsread2.news.atl.earthlink. net>, "Dan
Nuttle" <d_******@hotmail.com> wrote:

You don't technically gain anything by doing this. However, I'm a believer
in declaring variables whenever possible at the top of a class or method.
Instead of having variable declarations scattered all over. So I tend to
have lots of lines like

MyObject _o = null;

at the top of a class or method. That way, when I see a variable and I
don't know what type it is, I can look at the top of the class or method and
quickly find out. You can just declare the variable without setting it to
null, but then your class might not compile unless every single method that
uses the variable makes sure it's been initialized.

Some coding philosophies consider it very bad form to declare and
instantiate a variable at the same time, in the body of a method, like this:

public void myMethod()
{

//Some code here
String myString = "ABC";

}

But this is more of a philosophy than a technology issue.
"Dado" <dz****@mail.inet.hr> wrote in message
news:ci**********@sunce.iskon.hr...

I lost the point:
What is purpose of putting objects to null:

If I make a class, JFrame for example, with button which start connection
dialog, which is class with connection and statement Object.
And every time I click the button first I put :
dialog = null
dialog = new dialog()

What is purpose to put dialog = null when all its objects are stay

non-null?

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Checked by AVG anti-virus system (http://www.grisoft.com).
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