Question: What does setAutoCommit do?

Answer: When a connection is created, it is in auto-commit mode. This means that each individual SQL statement is treated as a transaction and will be automatically committed right after it is executed. The way to allow two or more statements to be grouped into a transaction is to disable auto-commit mode:
con.setAutoCommit(false);

Once auto-commit mode is disabled, no SQL statements will be committed until you call the method commit explicitly.

con.setAutoCommit(false);
PreparedStatement updateSales =
con.prepareStatement( "UPDATE EMPLOYEE SET SAL = ? WHERE EMP_NAME LIKE ?");
updateSales.setInt(1, 50000); updateSales.setString(2, "Arindam");
updateSales.executeUpdate();
PreparedStatement updateTotal =
con.prepareStatement("UPDATE EMPLOYEE SET TOTAL = TOTAL + ? WHERE EMP_NAME LIKE ?");
updateTotal.setInt(1, 50000);
updateTotal.setString(2, "Arindam");
updateTotal.executeUpdate();
con.commit();
con.setAutoCommit(true);