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The compilation mechanism in java
Unlike C and C++,java compiles the source text into binary code separately not a single executable application, which also determines the method java stores the references of other objects and links them when needs.Besides, the class binary code are coded wi ...
Java Generic Types
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- Java
A generic type is a generic class or interface that is parameterized over types. It can be used to generalize the type of parameters and return value in coding without the risk to pass a wrong type to its methods. Like the following example:
/**
* Generic version of the Box class.
* @param &l ...
Search text in tail or view command:
/to search text, search forward
?to search text, search backward
GZIP,TAR,ZIP
gzip is used to compress file large that 4GB, and it defaultes to preserve the name,ownership of the file. to unzip, only need -d parameter.
gzip files to compress
ta ...
Import/Export Database:
exp username/password@tns name FILE=D:\pub.dump OWNER=(username)
imp username/password name FILE=D:\pub.dump TOUSER=(username) FROMUSER=(username)
Query all users in the database:
select * from all_users;
Check the resource limits in oracle:
select * from v$r ...
Error Message:
Caused by: java.sql.SQLException: Listener refused the connection with the following error:
ORA-12519, TNS:no appropriate service handler found
The Connection descriptor used by the client was:
localhost:1521:xe
Cause:
This error is generally caused by the value of allowed pro ...
To change the HTTP and FTP ports for Oracle XMLDB, we only need to call the following command in Oracle with DBA role.
change HTTP port from 8080 to 9999
call dbms_xdb.cfg_update(updateXML(dbms_xdb.cfg_get(), '/xdbconfig/sysconfig/protocolconfig/httpconfig/http-port/text()', 9999));
...
The exists condition is considered to be met if the subquery returns more than one row. It always used to test whether relevant recrods exist and filter out those extraneous results.
The common case is that A object and B object have an association, which contains all the relationships between A an ...
Introduction
Transaction is a mechanism to ensure a bunch of database operations be performed in an atomic way. Either all of the operations succeed(committed) or nothing will be persisted(rollback). By default, a sql statement will begin a transaction if there is no transaction exists in the connec ...
Start from the web.xml
Every web application has a web descriptor which will be parsed by the web server.So it is prefered to start learning with the sample application from the web.xml file.There is a tag called context-param
, from its literal meaning i can know that the parameters defined ...