The function and instructions for use of Java

Function and use of ()

Recently, when I was looking at some code, I used(),(), etc. in many places.

System can have streams of standard input, standard output, error output; access to externally defined properties and environment variables; methods to load files and libraries; and also practical methods to quickly copy part of an array () to determine the current system attributes, and the return value is a Properties;

• (String filename)Equivalent to: ().load(String filename) Their function is to load code files with specified file names from the local file system as dynamic libraries.
• (Properties propes)Set system properties to Properties parameter;
• (String key,String value)Equivalent to ().setProperties(String key,String value): Set the system properties indicated by the specified key

setProperties

public static void setProperties(Properties props)

Set system properties toProperties

First, if there is a security manager, it will be called directly without parameters.checkPropertiesAccessmethod. This can lead to a security exception.

The parameters aregetProperty(String)A collection of current system properties used by the method. If the parameter isnull, the collection of current system attributes is ignored.

parameter:- New system properties.SecurityException``checkPropertiesAccessSee also:

public static Properties getProperties()

Determine the current system properties.

First, if there is a security manager, it will be called directly without parameters.checkPropertiesAccessmethod. This can lead to a security exception.

WillgetProperty(String)The current system attribute set used by the method isPropertiesObject returns. If there is no current system attribute collection, a system attribute collection is created and initialized first.

This system attribute set always contains the following key values:

Description of key-related values

Multiple paths in system attribute values ​​are separated by platform path separators.

Note that even if the security manager does not allow executiongetPropertiesIt may also choose to allow executiongetProperty(String)operate.

**return:**Throw:- If the Security Manager exists and its method does not allow access to system properties.setProperties()()Properties

Java code

public class TestSystemGetSet {  
    static{  
        ("DB", "mysql");// Can be used as a global variable anywhere    }  
    public static void main(String[] args) {  
        ((""));  
        ((""));  
        (("DB"));  
    }  
}  

Output result:

10.0
C:\Java\jdk1.8.0_121\bin;C:\WINDOWS\Sun\Java\bin;C:\WINDOWS\system32;C:\WINDOWS;C:/Java/jre8/bin/server;C:/Java/jre8/bin;C:/Java/jre8/lib/amd64;C:\Program Files\IBM\WebSphere MQ\java\lib;C:\Program Files\IBM\WebSphere MQ\java\lib64;E:\app\Administrator\product\11.2.0\dbhome_2\bin;C:\ProgramData\Oracle\Java\javapath;C:\WINDOWS\system32;C:\WINDOWS;C:\WINDOWS\System32\Wbem;C:\WINDOWS\System32\WindowsPowerShell\v1.0\;C:\Program Files\MySQL\MySQL Server 5.1\bin;D:/maven\bin;C:\Program Files (x86)\Rational\common;C:\Program Files\IBM\WebSphere MQ\bin64;C:\Program Files\IBM\WebSphere MQ\bin;C:\Program Files\IBM\WebSphere MQ\tools\c\samples\bin;C:\Java\jdk1.8.0_121\bin;C:\Users\Administrator\AppData\Local\Microsoft\WindowsApps；D:\maven\bin;E:\soft\apache-ant-1.10.1\bin;D:\erl9.2\bin;;C:\Users\Administrator\AppData\Local\Microsoft\WindowsApps;E:\tool\eclipse;;.
mysql

Summarize

The above is personal experience. I hope you can give you a reference and I hope you can support me more.