Java Web Instance Training knowledge Error Summary (i.)

1. Error 1002 in database

There are multiple foreign keys, and duplicate foreign key names occur. Change it on the line.

2. Database properties are automatically incremented

One is the automatic growth of fields in the table.
The other is the automatic growth of the database tablespace file.

When you create a 100M size data file for this database A on disk a_dat.dbf, all the information in database A will be stored in this file. When this 100M is exhausted, you need to decide what to do with the database.

1, error, unable to insert data.
2, the automatic expansion of this a_dat.dbf, such as each expansion of ten m, then when full after the automatic growth of "M", the next is the M

Method Two, if you encounter a malicious attack or an unexpected failure, resulting in large amounts of data inserted will produce huge files, resulting in the full computer disk is occupied, resulting in a complete computer outage. Therefore, it is not recommended.

Static keyword in 3.Java

Define a method as static in a class and call this method without an object of this class

The method declared as static has the following limitations:
· They can only invoke other static methods.
· They can only access static data.
· They cannot refer to this or super in any way.

Calling a static method is the class name. Method Name. In general, static methods are often used by other classes in the application, and in Java's class libraries a large number of static methods are defined for this purpose.

Reproduced from

4. Factory mode

Java Web Instance Training knowledge Error Summary (i.)