Ajay Divakaran

How do I rectify this error?

java Client.SimpleSessionClient

Exception in thread "main" javax.naming.NoInitialContextException: Cannot instan
tiate class: org.jnp.interfaces.NamingContextFactory [Root exception is java.lan
g.ClassNotFoundException: org.jnp.interfaces.NamingContextFactory]
at javax.naming.spi.NamingManager.getInitialContext(Unknown Source)
at javax.naming.InitialContext.getDefaultInitCtx(Unknown Source)
at javax.naming.InitialContext.init(Unknown Source)
at javax.naming.InitialContext.<init>(Unknown Source)
at Client.SimpleSessionClient.main(SimpleSessionClient.java:7)
Caused by: java.lang.ClassNotFoundException: org.jnp.interfaces.NamingContextFac
tory
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClassInternal(Unknown Source)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Unknown Source)
at com.sun.naming.internal.VersionHelper12.loadClass(Unknown Source)
... 5 more

I have Oracle9i installed.
When I run this program I get an sql exception on line 8 stating that "could not resolve service name"
import java.sql.*; public class TestOCIApp { public static void main(String args[]) throws ClassNotFoundException,SQLException { Class.forName("oracle.jdbc.driver.OracleDriver"); Connection conn = DriverManager.getConnection("jdbc:oracle:oci:@dssora01.dss","scott","tiger"); Statement stmt = conn.createStatement(); ResultSet rset = stmt.executeQuery( "select 'Hello OCI driver tester '||USER|| '!' result from dual"); while(rset.next()) System.out.println(rset.getString(1)); rset.close(); stmt.close(); conn.close(); } }

String s="|-|-|";

Using Pattern and Matcher in java.util.regex.* how do i write a RE
to match one or more occurance of "|-|"

String tp ="... --- ...";
tp=tp.replaceAll("...","O");

output : OOO..
should'nt it be O --- O

Pls. explain

If the default hashCode() produces distinct values for each object created
why do we need to override it when using Maps ?
If two objects having same instances are created naturally equals() ( which is overriden ) will return false and will not get stored in a map.
So is not efficient enough to just override equals() for high performance ( fast access ) because each object is in a distinct 'bucket' and searching and comparing with just one object in the 'bucket' is required ?

The code is correct!

Does the default hashCode() return unique number for each new object created?

I thought the default hashCode() returns a unique number for each object created?

import java.util.*;
class GenLearn
{
public static void main( String args[] )
{
ArrayList<Integer> input = new ArrayList<Integer>();
input.add(5);
List<Integer> output ;//= new ArrayList<Integer>();
output = process( input ); //error!!

}
public static <E extends Number> List<? super E> process( List<E> nums)
{
List<Integer> tp = new ArrayList<Integer>();
tp.add(6);
return tp; // error!!

}

Oh!! I forgot.
its called covariant return type
thank You!

If im correct, we can't overload based only on return type. But the example from K&B shows that it is possible and it is said to be an OVERRIDE !
How is it possible an overriden method having different return types ??
referring to the
getRental method in both classes

class Rental
{
private List rentalPool;
private int maxNum;
public Rental( int maxNum, List rentalPool )
{
this.maxNum = maxNum;
this.rentalPool = rentalPool;
}
public Object getRental()
{
return rentalPool.get(0);
}
}
class CarRental extends Rental
{
public CarRental( int maxNum, List<Car> rentalPool )
{
super( maxNum, rentalPool );
}
public Car getRental() // how can it be an override ??
{
return (Car)super.getRental();
}
}

im reading byte by byte

i got the o/p as
19 11

How can I browse through all the file systems such as C,D,E and so on..
How do I know what drives are present on the computer??

How do i read the number -1 from the file because end of file is also -1??