The following is the Application class:::: and I'm getting an error saying "Duplicate entry 101 for Primary Key"

package manytomany;

import java.util.HashSet;
import java.util.Set;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.Transaction;
import org.hibernate.cfg.Configuration;

public class ManyToMany{

public static void main(String args[])
{

SessionFactory factory = new Configuration().configure().buildSessionFactory();
Session session = factory.openSession();

Student s1=new Student();
s1.setStudentId(100);
s1.setStudentName("James");
s1.setMarks(98);

Student s2=new Student();
s2.setStudentId(101);
s2.setStudentName("Lee");
s2.setMarks(99);

Courses c1=new Courses();
c1.setCourseId(500);
c1.setCourseName("Hibernate");
c1.setDuration(7);

Courses c2=new Courses();
c2.setCourseId(501);
c2.setCourseName("Java");
c2.setDuration(30);

Set s =new HashSet();
s.add(c1);
s.add(c2);

s1.setCourses(s);
s2.setCourses(s);

Transaction tx = session.beginTransaction();

session.save(s1);
session.save(s2);

tx.commit();

session.close();
System.out.println("Many To Many Bi-Directional is Done..!!");
factory.close();

}
}

The following is the complete error:::::::
WARNING: SQL Error: 1062, SQLState: 23000
Apr 20, 2013 9:21:06 AM org.hibernate.util.JDBCExceptionReporter logExceptions
SEVERE: Duplicate entry '101' for key 'PRIMARY'
Apr 20, 2013 9:21:06 AM org.hibernate.event.def.AbstractFlushingEventListener performExecutions
SEVERE: Could not synchronize database state with session
org.hibernate.exception.ConstraintViolationException: Could not execute JDBC batch update
at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:71)
at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:43)
at org.hibernate.jdbc.AbstractBatcher.executeBatch(AbstractBatcher.java:253)
at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:237)
at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:145)
at org.hibernate.event.def.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:298)
at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:27)
at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1000)
at org.hibernate.impl.SessionImpl.managedFlush(SessionImpl.java:338)
at org.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:106)
at manytomany.ManyToMany.main(ManyToMany.java:51)
Caused by: java.sql.BatchUpdateException: Duplicate entry '101' for key 'PRIMARY'
at com.mysql.jdbc.PreparedStatement.executeBatchSerially(PreparedStatement.java:2028)
at com.mysql.jdbc.PreparedStatement.executeBatch(PreparedStatement.java:1451)
at org.hibernate.jdbc.BatchingBatcher.doExecuteBatch(BatchingBatcher.java:48)
at org.hibernate.jdbc.AbstractBatcher.executeBatch(AbstractBatcher.java:246)
... 8 more
Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Duplicate entry '101' for key 'PRIMARY'
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:525)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
at com.mysql.jdbc.Util.getInstance(Util.java:386)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1039)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3609)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3541)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2002)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2163)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2624)
at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:2127)
at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2427)
at com.mysql.jdbc.PreparedStatement.executeBatchSerially(PreparedStatement.java:1980)
... 11 more

Exception in thread "main" org.hibernate.exception.ConstraintViolationException: Could not execute JDBC batch update
at org.hibernate.exception.SQLStateConverter.convert(SQLStateConverter.java:71)
at org.hibernate.exception.JDBCExceptionHelper.convert(JDBCExceptionHelper.java:43)
at org.hibernate.jdbc.AbstractBatcher.executeBatch(AbstractBatcher.java:253)
at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:237)
at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:145)
at org.hibernate.event.def.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:298)
at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:27)
at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1000)
at org.hibernate.impl.SessionImpl.managedFlush(SessionImpl.java:338)
at org.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:106)
at manytomany.ManyToMany.main(ManyToMany.java:51)
Caused by: java.sql.BatchUpdateException: Duplicate entry '101' for key 'PRIMARY'
at com.mysql.jdbc.PreparedStatement.executeBatchSerially(PreparedStatement.java:2028)
at com.mysql.jdbc.PreparedStatement.executeBatch(PreparedStatement.java:1451)
at org.hibernate.jdbc.BatchingBatcher.doExecuteBatch(BatchingBatcher.java:48)
at org.hibernate.jdbc.AbstractBatcher.executeBatch(AbstractBatcher.java:246)
... 8 more
Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Duplicate entry '101' for key 'PRIMARY'
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:525)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
at com.mysql.jdbc.Util.getInstance(Util.java:386)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1039)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3609)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3541)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2002)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2163)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2624)
at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:2127)
at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2427)
at com.mysql.jdbc.PreparedStatement.executeBatchSerially(PreparedStatement.java:1980)
... 11 more
Java Result: 1

Check your student table it must be having 101 already