Thread: Ask about autocommit etc.

Hello everybody, i am new in Java Programming language.. I have a confussion when i try to develop database on my application.. Oke, this is my confussion.

public boolean updateBook(Book b){
        String query = "UPDATE BOOK SET "
        + "id=?, categori=?, title=?, date=?, source=?, number=?, "
        + "year=?, count=?"
        + "WHERE id=?";
        PreparedStatement statement=null;
        try {
            statement = connection.prepareStatement(query);
            for(int i=1;i<=8;i++)
                statement.setObject(i, b.getObject(i));
            statement.setInt(9, b.getId());
            connection.setAutoCommit(false);
            if(statement.executeUpdate()==1)
                connection.commit();
        } catch (SQLException ex) {
            JOptionPane.showMessageDialog(null, "Error when update data\n Error: "+ex.getMessage());
            try { connection.rollback(); } catch (SQLException exr) {}
            return false;
        }finally{try {if(statement != null)statement.close(); } catch (Exception e) { }}
        return true;
    }

I want to know:
1. Why the "connection.setAutoCommit()" is used?
2. When should i set the "connection.setAutoCommit(false)" to "false" or set to "true"?
3. Why the "connection.commit();" is used?
4. Why in the try and catch, are used the "connection.rollback();" ? What is the meaning of this?

I hope at least one of you can give me explanation about my trouble above.
Please help me to solve it.. Thank you very much. GBU All..

It is called a Transaction. See the following:
Using Transactions (The Java™ Tutorials > JDBC(TM) Database Access > JDBC Basics)