system getenv

系統類getenv()方法 (System class getenv() method)

• getenv() method is available in java.lang package.

  getenv()方法在java.lang包中可用。

• getenv() method is used to return an unmodifiable Map of the current environment variable in key-value pairs.

  getenv()方法用于返回鍵值對中當前環境變量的不可修改Map。

• We will see what is environment variable ? An environment variable is a system dependent external named value.

  我們將看到什么是環境變量？ 環境變量是系統相關的外部命名值。

• We should go for environment variable when a system interface needed an environment variable (such as PATH).

  當系統接口需要環境變量(例如PATH)時，我們應該選擇環境變量。

• When we assign the value of the environment variable then we don’t need to assign the value of the environment variable again while working.

  當我們分配環境變量的值時，我們就不需要在工作時再次分配環境變量的值。

• getenv() method is a static method so it is accessible with the class name too.

  getenv()方法是靜態方法，因此也可以使用類名進行訪問。

• getenv() method method may throw an exception at the time of retrieving the environment variable:

  getenv()方法 method可能在檢索環境變量時引發異常：

  SecurityException: If a particular method checkPermission() does not allow access to the process environment when the security manager exists.

  SecurityException ：如果存在安全管理器時，如果特定方法checkPermission()不允許訪問流程環境。

Syntax:

句法：

    public static Map getenv ();

Parameter(s):

參數：

• This method does not accept any parameter.

  此方法不接受任何參數。

Return value:

返回值：

The return type of this method is Map, it returns the environment variable with the desired value.

此方法的返回類型為Map ，它返回具有所需值的環境變量。

Example:

例：

// Java program to demonstrate the example of 
// getenv() method of System Class.
import java.util.*;
import java.lang.*;
public class GetenvMethod {
public static void main(String[] args) {
Map < String, String > map = System.getenv();
// By using keyset() method is used to iterate
Set < String > system_keys = map.keySet();
for (String keys: system_keys) {
System.out.println("system_key= " + keys);
String values = map.get(keys);
System.out.println("system_key_value= " + values);
}
}
}

Output

輸出量

E:\Programs>javac GetenvMethod.java
E:\Programs>java GetenvMethod
system_key= PATH
system_key_value= /usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/lib/jvm/java-10-jdk/bin
system_key= SHELL
system_key_value= /bin/bash
system_key= HOSTNAME
system_key_value= jdoodle
system_key= JAVA_OPTS
system_key_value= --add-opens=java.base/java.lang=ALL-UNNAMED --add-opens=java.base/java.lang.invoke=ALL-UNNAMED
system_key= PWD
system_key_value= /home
system_key= SHLVL
system_key_value= 1
system_key= HOME
system_key_value= /root
system_key= _
system_key_value= /usr/bin/time

翻譯自: https://www.includehelp.com/java/system-class-getenv-method-with-example.aspx

system getenv