JDBC Interview Questions and Answers

How do I display and parse a date?
The Java I18N way is to use a DateFormat. While SimpleDateFormat, which is generally returned, creates a large number of objects, it is locale aware and will handle most of your needs. The following sample code initially creates a java.sql.Date object and formats it for the default locale. An initial actionPerformed call additionally formats/displays it for a German locale and also displays the resulting java.sql.Date in standard escape format. Other dates can be entered and parsed after the initial display.

// JDFDP.java - Display and Parse java.sql.Date

import java.sql.*;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.text.*;
import java.util.*;

public class JDFDP extends JFrame
implements ActionListener,
WindowListener
{
// create a java.sql.Date
java.sql.Date jsqlDate = new java.sql.Date(
System.currentTimeMillis() );

DateFormat dfLocal = DateFormat.getDateInstance(
DateFormat.SHORT );
DateFormat dfGermany = DateFormat.getDateInstance(
DateFormat.SHORT, Locale.GERMANY );

JButton jb = new JButton( "Go" );
JLabel jlI = new JLabel("Input a Date:"),
jlD = new JLabel("Display German:"),
jlP = new JLabel("Parsed:");

JPanel jp = new JPanel();

JTextField jtI = new JTextField( 10 ),
jtD = new JTextField( 10 ),
jtP = new JTextField( 10 );

public JDFDP()
{
super( "JDFDP" );
addWindowListener( this );

jb.addActionListener( this );

jp.add(jlI);
jp.add(jtI);
jp.add(jb);
jp.add(jlD);
jp.add(jtD);
jp.add(jlP);
jp.add(jtP);

getContentPane().add( jp, BorderLayout.CENTER );
pack();

// set text by sending dummy event
jtI.setText( dfLocal.format( jsqlDate ) );
actionPerformed(
new ActionEvent( this, 12, "12" ) );

show();

} // end constructor

// ActionListener Implementation
public void actionPerformed(ActionEvent e)
{
jtD.setText( "" );
jtP.setText( "" );
try
{
java.util.Date d = dfLocal.parse(
jtI.getText() );
jtI.setText( dfLocal.format( d ) );
jtD.setText( dfGermany.format( d ) );
d = dfGermany.parse( jtD.getText() );
// get new java.sql.Date
jsqlDate = new java.sql.Date( d.getTime() );

jtP.setText( jsqlDate.toString() );
}
catch( ParseException pe ) { jtI.setText( "" ); }

} // End actionPerformed

// Window Listener Implementation
public void windowOpened(WindowEvent e) {}
public void windowClosing(WindowEvent e)
{
dispose();
System.exit(0);
}
public void windowClosed(WindowEvent e) {}
public void windowIconified(WindowEvent e) {}
public void windowDeiconified(WindowEvent e) {}
public void windowActivated(WindowEvent e) {}
public void windowDeactivated(WindowEvent e) {}
// End Window Listener Implementation

public static void main(String[] args)
{
new JDFDP();
}

} // end class JDFDP

How can I retrieve string data from a database in Unicode format?
The data is already in Unicode when it arrives
in your program. Conversion from and to the
encoding/charset/CCSID in the database from/to
Unicode in the program is part of the JDBC driver's job.

If, for some reason, you want to see the data in
'\uHHHH' format ( where 'H' is the hex value ),
the following code, while not very efficient,
should give you some ideas:

public class UniFormat
{

public static void main( String[] args )
{
char[] ac = args[0].toCharArray();
int iValue;
String s = null;
StringBuffer sb = new StringBuffer();

for( int ndx = 0; ndx < ac.length; ndx++ )
{
iValue = ac[ndx];

if( iValue < 0x10 )
{
s = "\\u000";
}
else
if( iValue < 0x100 )
{
s = "\\u00";
}
else
if( iValue < 0x1000 )
{
s = "\\u0";
}

sb.append( s + Integer.toHexString( iValue ) );
} // end for

System.out.println("The Unicode format of " +
args[0] + " is " + sb );

} // end main

} // end class UniFormat

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