What is going on with:
outCel.setText( celsTemp+"" );
Answer:
The text that appear in the text field outCel
is set with its setText method.
That parameter for that method should be reference to a String.
But celsTemp is an integer, and will not work.
However in the following,
celsTemp+""
+ means "string concatenation" so the integer
in celsTemp is converted to a String,
an empty string is concatenated onto it,
which results in a String, which is the proper type for the parameter.
Complete Application
The complete application is below.
Of course, you will want to copy this
to a file, compile and run it.
import java.awt.*;
import java.awt.event.*;
import javax.swing.* ;
public class FahrConvert extends JFrame implements ActionListener
{
JLabel heading = new JLabel("Convert Fahrenheit to Celsius");
JLabel inLabel = new JLabel("Fahrenheit ");
JLabel outLabel = new JLabel("Celsius ");
JTextField inFahr = new JTextField( 7 );
JTextField outCel = new JTextField( 7 );
int fahrTemp ;
int celsTemp ;
FahrConvert( String title )
{
super( title );
setLayout( new FlowLayout() );
inFahr.addActionListener( this );
outCel.setEditable( false );
add( heading );
add( inLabel );
add( outLabel );
add( inFahr );
add( outCel );
setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
}
// The application
public int convert( int F )
{
return ( (F-32) * 5 ) / 9;
}
public void actionPerformed( ActionEvent evt)
{
String userIn = inFahr.getText() ;
fahrTemp = Integer.parseInt( userIn ) ;
celsTemp = convert( fahrTemp ) ;
outCel.setText( celsTemp+"" );
repaint();
}
public static void main ( String[] args )
{
FahrConvert fahr = new FahrConvert( "F to C" ) ;
fahr.setSize( 200, 150 );
fahr.setVisible( true );
}
}
