enable checkbox question

[Vonique Leary]

In my beginning Java Programming workbook there is an example of toggling between setting the checkbox enabled or disabled, but I'm not quite sure I get it. The instructor couldn't really explain it to me except to say that it is toggling because of the ! operator:

   

public void checkmyButton() {

checkbox.setEnabled(!checkbox.isEnabled()); 

}

 

Can anyone explain this to me? What does the !checkbox.isEnabled() method return to checkbox.setEnabled that does the opposite of what is is now?

Thanks, Vonuu

[Frankey James]

checkbox.isEnabled // returns a bool of true of false.

checkbox.setEnabled() //requires a bool to determine if the checkbox should be enabled or not

!checkbox.isEnabled means to inverse (or toggle) the CURRENT value of checkbox.isEnabled by negating the current value witht he ! operator

So checkbox.setEnabled(!checkbox.isEnabled()); so this is changing the current state (enabled or not) to the opposite of what it currenlt is

more lines of code example could look like this:

//disable checkbox if it's enabled, and enable it if it's currently not enabled
if(checkbox.isEnabled == true){

checkbox.setEnabled(false);

}else if(checkbox.isEnabled == flase){

checkbox.setEnabled(true);
}


Make cents?

[Campbell Ritchie]

Good explanation (barring the dreadful pun in the last line), but never use == true or == false. They are prone to nasty errors if you manage to write = instead of ==.

If you use the CODE button as you ought, you get:

//disable checkbox if it's enabled, and enable it if it's currently not enabled
if (checkbox.isEnabled())
{
   checkbox.setEnabled(false);
}
else if (!checkbox.isEnabled())
{
   checkbox.setEnabled(true);
}

I think Vonique's original example more elegant.

[Vonique Leary]

Thanks, yes that makes a lot of cents to me now! I like the pun, too.

Great explanation!

Von

[Campbell Ritchie]

Vonique Leary wrote:I like the pun, too.

Aaaargh!