if not null

In versions earlier than JDK, when an object is not referenced by any variable, the program will no longer be able to use this object. That is to say, the program can use the object only when it is reachable. This is like in daily life, after buying

Basic MySQL database operation commands====================================== I. MySQL service operations 0. Check the database version SQL> status;1. Net start MySQL // start the MySQL Service2. net stop MySQL // stop MySQL Service3. mysql-H host

-- Duplicate null columns can be detected.Delete From [ Jcxs0201 ] Where User_id In ( Select User_id U From [ Jcxs0201 ] Group By User_id Having Count (ID) > 1 ) And ID Not In ( Select Min (ID) From [ Jcxs02

Section II. Analysis of GC key methods 1. Dispose () method Dispose can be used to release all resources, including hosted and unmanaged resources. Most of the unmanaged resources require manual release. We should publish a method to release

 All classes are ultimately inherited from system. object.  Therefore, the inheritance class will have the object's instance method: 1. equals 2. gethashcode 3. tostring 4. GetType 5. memberwiseclone. 6. Finalize Where tostring ()

Character string date math others: isnull convert row_number select Len ('dshgjkdhsad ') returns the number of characters in the specified string expression, excluding trailing spaces. Itrim ('anc skkmkls') returns the string expression after the

1. The collection framework acts as a container for processing objects. The basic interface is collection. Compared with arrays, the collection framework can only store objects, but its length is variable. The relationship diagram of the Collection

-- If ware_id has no data, it is 1Select nvl (A. ware_id, 1) from dtf_test; -- Partition to which the table is moved tablename table name new_name partition name --Alter table tablename moveTablespace new_nameStorage (initial 50 m next 50

0. Check the database version SQL> status;1. Net start MySQL // start the MySQL Service2. net stop MySQL // stop MySQL Service3. mysql-H host address-u user name-P User Password // enter the MySQL database4. Quit // exit MySQL5. mysqladmin-u

Reprinted: http://www.javaeye.com/topic/249851 Since learning to use jquery, I have never found a simple tree that supports asynchronous loading, but I have to extend it myself. The Treeview function of jquery's official UI is single and not small

In the 23 design modes of GOF, the singleton mode is a relatively simple one. However, sometimes the simpler things become more prone to problems. The following is a detailed discussion of the single-instance design pattern. The so-called singleton

: memcached Windows 64-bit1, extract to the specified directory, such as: D:\Memcached\memcached-win64-1.4.4-14.2, open the command window with CMD, go to the extracted directory, enter "memcached.exe-d install".3, open the Control Panel, open the

Hadoop Rack-aware1. BackgroundHadoop is designed to take into account the security and efficiency of data, data files by default in HDFs storage three copies, the storage policy is a local copy,A copy of one of the other nodes in the same rack, a

　　Last time I said that the current page needs to load more than one data class, and the foreground page only has a form form, how do we do the data echo.To solve this problem, the team members discussed the ability to return data to the page

  ① Out-javax. servlet. jsp. jspwriter The out object is used to output the result to the webpage. Method: 1. Void clear (); Clears the content of the output buffer but does not output it to the client. 2. Void clearbuffer (); Clear the content of

?? "Null coalescing" operator Is a new operator provided by c #. The function provided by this operator is to determine whether the left-side operand is null. If yes, the return result is the right-side operand, and if not null, the left-side

C # Serial Communication ProgrammingIvanxBy This article describes how to use C # To create a serial communication program on the. NET platform. NET 2.0 provides the serial communication function. Its namespace is System. IO. Ports. We will use

1. Is action thread-safe? If there is no way to ensure the thread security of action? If yes, explain the reasonAction is NOT thread-safe. Thread security can be ensured without declaring class variables. Because only one action instance exists, all

Chapter 3 Protecting the Data (1): Understanding permissions, chapterprotectingSource: Workshop Without the consent of the author, no one shall be published in the form of "original" or used for commercial purposes. I am not responsible for any

The reason for putting constraints and indexes together is mainly because of primary key constraints and unique key constraints. They will automatically create a corresponding index. Let's look at the constraints in the database. 1 Constraint In