Question

I am following a basic hibernate tutorial. The tutorial program is running & showing output as described in the tutorial but it is showing exception after the output. The program writes, retrieves, & deletes values in/from two MySql database.
Here is the exception:

29088 [main] ERROR org.hibernate.jdbc.AbstractBatcher - Exception executing batch: 
org.hibernate.StaleStateException: Batch update returned unexpected row count from update [0]; actual row count: 0; expected: 1
    at org.hibernate.jdbc.Expectations$BasicExpectation.checkBatched(Expectations.java:85)
    at org.hibernate.jdbc.Expectations$BasicExpectation.verifyOutcome(Expectations.java:70)
    at org.hibernate.jdbc.BatchingBatcher.checkRowCounts(BatchingBatcher.java:90)
    at org.hibernate.jdbc.BatchingBatcher.doExecuteBatch(BatchingBatcher.java:70)
    at org.hibernate.jdbc.AbstractBatcher.executeBatch(AbstractBatcher.java:268)
    at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:266)
    at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:172)
    at org.hibernate.event.def.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:321)
    at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:50)
    at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1027)
    at org.hibernate.impl.SessionImpl.managedFlush(SessionImpl.java:365)
    at org.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:137)
    at com.hib.Test.deleteUser(Test.java:187)
    at com.hib.Test.main(Test.java:55)
Hibernate: delete from users where id=?
29093 [main] ERROR org.hibernate.event.def.AbstractFlushingEventListener - Could not synchronize database state with session
org.hibernate.StaleStateException: Batch update returned unexpected row count from update [0]; actual row count: 0; expected: 1
    at org.hibernate.jdbc.Expectations$BasicExpectation.checkBatched(Expectations.java:85)
    at org.hibernate.jdbc.Expectations$BasicExpectation.verifyOutcome(Expectations.java:70)
    at org.hibernate.jdbc.BatchingBatcher.checkRowCounts(BatchingBatcher.java:90)
    at org.hibernate.jdbc.BatchingBatcher.doExecuteBatch(BatchingBatcher.java:70)
    at org.hibernate.jdbc.AbstractBatcher.executeBatch(AbstractBatcher.java:268)
    at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:266)
    at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:172)
    at org.hibernate.event.def.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:321)
    at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:50)
    at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1027)
    at org.hibernate.impl.SessionImpl.managedFlush(SessionImpl.java:365)
    at org.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:137)
    at com.hib.Test.deleteUser(Test.java:187)
    at com.hib.Test.main(Test.java:55)
org.hibernate.StaleStateException: Batch update returned unexpected row count from update [0]; actual row count: 0; expected: 1
    at org.hibernate.jdbc.Expectations$BasicExpectation.checkBatched(Expectations.java:85)
    at org.hibernate.jdbc.Expectations$BasicExpectation.verifyOutcome(Expectations.java:70)
    at org.hibernate.jdbc.BatchingBatcher.checkRowCounts(BatchingBatcher.java:90)
    at org.hibernate.jdbc.BatchingBatcher.doExecuteBatch(BatchingBatcher.java:70)
    at org.hibernate.jdbc.AbstractBatcher.executeBatch(AbstractBatcher.java:268)
    at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:266)
    at org.hibernate.engine.ActionQueue.executeActions(ActionQueue.java:172)
    at org.hibernate.event.def.AbstractFlushingEventListener.performExecutions(AbstractFlushingEventListener.java:321)
    at org.hibernate.event.def.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:50)
    at org.hibernate.impl.SessionImpl.flush(SessionImpl.java:1027)
    at org.hibernate.impl.SessionImpl.managedFlush(SessionImpl.java:365)
    at org.hibernate.transaction.JDBCTransaction.commit(JDBCTransaction.java:137)
    at com.hib.Test.deleteUser(Test.java:187)
    at com.hib.Test.main(Test.java:55)

This is main program.

package com.hib;

import java.util.Iterator;
import java.util.List;
import org.hibernate.Session;
import org.hibernate.Transaction;

public class Test {

 /**
  * @param args
  */
 public static void main(String[] args) {

  Test tst = new Test();

  /**
   * adding records
   */
  tst.addUser("Saranga", "Rath");
  tst.addUser("Isuru", "Sampath");
  tst.addUser("Saranga", "Jaya");
  tst.addUser("Prasanna", "Milinda");

  tst.addTask(1, "Call", "Call Pubudu at 5 PM");
  tst.addTask(1, "Shopping", "Buy some foods for Kity");
  tst.addTask(2, "Email", "Send birthday wish to Pubudu");
  tst.addTask(2, "SMS", "Send message to Dad");
  tst.addTask(2, "Office", "Give a call to Boss");

  /**
   *  retrieving data
   */
  tst.getFullName("Saranga");

  /**
   * full updating records
   */
  User user = new User();
  user.setId(1);
  user.setFirstName("Saranga");
  user.setLastName("Rathnayake");
  tst.updateUser(user);

  /**
   * partial updating records
   */
  tst.updateLastName(3, "Jayamaha");

  /**
   * deleting records
   */
  User user1 = new User();
  user1.setId(4);
  tst.deleteUser(user1);
 }

 private void addUser(String firstName, String lastName) {

  Transaction trns = null;
  Session session = HibernateUtil.getSessionFactory().openSession();
  try {
   trns = session.beginTransaction();

   User user = new User();

   user.setFirstName(firstName);
   user.setLastName(lastName);

   session.save(user);

   session.getTransaction().commit();
  } catch (RuntimeException e) {
   if(trns != null){
    trns.rollback();
   }
   e.printStackTrace();
  } finally{
   session.flush();
   session.close();
  }
 }

 private void addTask(int userID, String title, String description) {

  Transaction trns = null;
  Session session = HibernateUtil.getSessionFactory().openSession();
  try {
   trns = session.beginTransaction();

   Task task = new Task();

   task.setUserID(userID);
   task.setTitle(title);
   task.setDescription(description);

   session.save(task);

   session.getTransaction().commit();
  } catch (RuntimeException e) {
   if(trns != null){
    trns.rollback();
   }
   e.printStackTrace();
  } finally{
   session.flush();
   session.close();
  }
 }

 private void updateLastName(int id, String lastName) {
  Transaction trns = null;
  Session session = HibernateUtil.getSessionFactory().openSession();
  try {
   trns = session.beginTransaction();
   String hqlUpdate = "update User u set u.lastName = :newLastName where u.id = :oldId";
   int updatedEntities = session.createQuery( hqlUpdate )
   .setString( "newLastName", lastName )
   .setInteger( "oldId", id )
   .executeUpdate();

   trns.commit();
  } catch (RuntimeException e) {
   if(trns != null){
    trns.rollback();
   }
   e.printStackTrace();
  } finally{
   session.flush();
   session.close();
  }

 }

 private void updateUser(User user) {
  Transaction trns = null;
  Session session = HibernateUtil.getSessionFactory().openSession();
  try {
   trns = session.beginTransaction();

   session.update(user);

   session.getTransaction().commit();
  } catch (RuntimeException e) {
   if(trns != null){
    trns.rollback();
   }
   e.printStackTrace();
  } finally{
   session.flush();
   session.close();
  }
 }

 private void getFullName(String firstName) {
  Transaction trns = null;
  Session session = HibernateUtil.getSessionFactory().openSession();
  try {
   trns = session.beginTransaction();
   List<User> users = session.createQuery("from User as u where u.firstName = :firstName")
   .setString( "firstName", firstName )
   .list();
   for (Iterator<User> iter = users.iterator(); iter.hasNext();) {
    User user = iter.next();
    System.out.println(user.getFirstName() +" " + user.getLastName());
   }
   trns.commit();
  } catch (RuntimeException e) {
   if(trns != null){
    trns.rollback();
   }
   e.printStackTrace();
  } finally{
   session.flush();
   session.close();
  }
 }

 private void deleteUser(User user) {
  Transaction trns = null;
  Session session = HibernateUtil.getSessionFactory().openSession();
  try {
   trns = session.beginTransaction();

   session.delete(user);

   session.getTransaction().commit();
  } catch (RuntimeException e) {
   if(trns != null){
    trns.rollback();
   }
   e.printStackTrace();
  } finally{
   session.flush();
   session.close();
  }
 }
}

HibernateUtil.java

package com.hib;

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

public class HibernateUtil {
 private static final SessionFactory sessionFactory = buildSessionFactory();
 private static SessionFactory buildSessionFactory() {
  try {
   // Create the SessionFactory from hibernate.cfg.xml
   return new Configuration().configure().buildSessionFactory();
  }
  catch (Throwable ex) {
   // Make sure you log the exception, as it might be swallowed
   System.err.println("Initial SessionFactory creation failed." + ex);
   throw new ExceptionInInitializerError(ex);
  }
 }
 public static SessionFactory getSessionFactory() {
  return sessionFactory;
 }
}

User.java

package com.hib;

public class User {
 private Integer id;
 private String firstName;
 private String lastName;

 public Integer getId() {
  return id;
 }
 public void setId(Integer id) {
  this.id = id;
 }
 public String getFirstName() {
  return firstName;
 }
 public void setFirstName(String firstName) {
  this.firstName = firstName;
 }
 public String getLastName() {
  return lastName;
 }
 public void setLastName(String lastName) {
  this.lastName = lastName;
 }
}

Task.java

package com.hib;

public class Task {

 private Integer id;
 private Integer userID;
 private String title;
 private String description;

 public Integer getId() {
  return id;
 }
 public void setId(Integer id) {
  this.id = id;
 }
 public Integer getUserID() {
  return userID;
 }
 public void setUserID(Integer userID) {
  this.userID = userID;
 }
 public String getTitle() {
  return title;
 }
 public void setTitle(String title) {
  this.title = title;
 }
 public String getDescription() {
  return description;
 }
 public void setDescription(String description) {
  this.description = description;
 }
}

Answer 1

This exception will occur if you try to delete or update a row that does not exist.
And this is exactly what you do:

User user1 = new User();
user1.setId(4);
tst.deleteUser(user1);

user1 is never persisted to the DB so how is hibernate supposed to delete it?

BTW: NEVER set an auto generated PK value of an entity yourself, this means trouble.
Also, I noticed that you reference User from Task by using the userID itself in Task. It is valid to relate this way using a Business Key (e.g. unique user email or such) if you want to separate the domains but pointless if you’re using the primary key. Instead of Integer userID, use User user in Task and create a ManyToOne with User.