Can't get a dialog box to work

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Steven M. Britton - 14 Mar 2004 20:00 GMT

lblEmpty = new JLabel("Aircraft Empty Weight",JLabel.LEFT);
panel.add(lblEmpty);

    txtEmpty = new JTextField("0",5);
txtEmpty.setSize(50,30); // Width, Heigth
panel.add(txtEmpty);

dblEmpty = Double.parseDouble(txtEmpty.getText());

            if (dblEmpty = null)
            JOptionPane.showMessageDialog(frame, "Empty Required");

I get the following error, what can I do to correct it?

incompatible types
found : double
required : boolean

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Lee Weiner - 14 Mar 2004 20:29 GMT

>lblEmpty = new JLabel("Aircraft Empty Weight",JLabel.LEFT);
> panel.add(lblEmpty);
[quoted text clipped - 13 lines]
>found : double
>required : boolean

You've got two errors in the "if" statement. First, the equality operator is
a double equal sign (==). You've got an assignment operator (=). Second, a
primitive variable cannot be null. What you have to do is test the length of
the String in the textfield before you parseDouble() it into the double
variable.
if( txtEmpty.getText().length() == 0 )
JOptionPane.showMessageDialog( blah, blah);
else
dblEmpty = Double.parseDouble( txtEmpty.getText() );

Lee Weiner
lee AT leeweiner DOT org

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Jon A. Cruz - 14 Mar 2004 20:45 GMT

> if( txtEmpty.getText().length() == 0 )
> JOptionPane.showMessageDialog( blah, blah);
> else
> dblEmpty = Double.parseDouble( txtEmpty.getText() );

To clean it up to be generally useful you can cache and check the text
differently.

String txt = txtEmpty.getText();

if ( txt == null || "".equals(txt) )
{
JOptionPane.showMessageDialog( blah, blah);
}
else
{
dblEmpty = Double.parseDouble( txt );
}

Although in this case you can count on getText() not being null, doing
the "if" like that makes it unified and easier when doing a cut-n-paste
to copy elsewhere.

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Jon A. Cruz - 14 Mar 2004 20:47 GMT

> txtEmpty.setSize(50,30); // Width, Heigth

Usually you don't want to do that.

Instead of trying to place each component manually, use a Layout Manager
to control the layout.

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Can't get a dialog box to work

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