If you call getenv() method in the class System, it will return the map containing all the environment variables configured in your system. If you just iterate the map, it will display all the details. This example shows the simple program to print the environment variables. I have executed this example in the Ubuntu Linux OS, but it will work in all the platform. I have used TreeMap to sort the order of the listing.

EnvironmentVariablesExample.java

[code lang=”java”]
package javabeat.net.core;

import java.util.Map;
import java.util.Set;
import java.util.SortedMap;
import java.util.TreeMap;

public class EnvironmentVariablesExample {
public static void main(String[] args) {
Map<String, String> environmentMap = System.getenv();
SortedMap<String, String> sortedEnvMap = new TreeMap<String, String>(environmentMap);
Set<String> keySet = sortedEnvMap.keySet();
for (String key : keySet) {
String value = environmentMap.get(key);
System.out.println("[" + key + "] " + value);
}
}
}
[/code]

Output…

[code]
[COMPIZ_CONFIG_PROFILE] ubuntu
[DBUS_SESSION_BUS_ADDRESS] unix:abstract=/tmp/dbus-ihV3MTXDtR,guid=9dd6a750057413f91d1e961d00000093
[DEFAULTS_PATH] /usr/share/gconf/ubuntu.default.path
[DESKTOP_SESSION] ubuntu
[DISPLAY] :0.0
[GDMSESSION] ubuntu
[GNOME_DESKTOP_SESSION_ID] this-is-deprecated
[GNOME_KEYRING_CONTROL] /tmp/keyring-x4RXST
[GNOME_KEYRING_PID] 1941
[GPG_AGENT_INFO] /tmp/keyring-x4RXST/gpg:0:1
[GTK_MODULES] canberra-gtk-module:canberra-gtk-module
[HOME] /home/krishna
[LANG] en_IN
[LANGUAGE] en_IN:en
[LD_LIBRARY_PATH] /usr/lib/jvm/java-6-openjdk-i386/jre/lib/i386/server:/usr/lib/jvm/java-6-openjdk-i386/jre/lib/i386:/usr/lib/jvm/java-6-openjdk-i386/jre/../lib/i386:/usr/lib/jvm/java-6-openjdk-i386/jre/lib/i386/client:/usr/lib/jvm/java-6-openjdk-i386/jre/lib/i386:
[LOGNAME] krishna
[MANDATORY_PATH] /usr/share/gconf/ubuntu.mandatory.path
[PATH] /usr/lib/lightdm/lightdm:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games
[PWD] /home/krishna
[SESSION_MANAGER] local/krishna-desktop:@/tmp/.ICE-unix/1952,unix/krishna-desktop:/tmp/.ICE-unix/1952
[SHELL] /bin/bash
[SSH_AGENT_PID] 1990
[SSH_AUTH_SOCK] /tmp/keyring-x4RXST/ssh
[UBUNTU_MENUPROXY] libappmenu.so
[USER] krishna
[XAUTHORITY] /home/krishna/.Xauthority
[XDG_CONFIG_DIRS] /etc/xdg/xdg-ubuntu:/etc/xdg
[XDG_CURRENT_DESKTOP] Unity
[XDG_DATA_DIRS] /usr/share/ubuntu:/usr/share/gnome:/usr/local/share/:/usr/share/
[XDG_SEAT_PATH] /org/freedesktop/DisplayManager/Seat0
[XDG_SESSION_COOKIE] 668183e0288a5cca221ebab100000007-1391125112.629260-1060816248
[XDG_SESSION_PATH] /org/freedesktop/DisplayManager/Session0
[/code]

If you are working on the tools development or similar product developments , then system level programming or OS interaction operations are necessary to access the native data. One of the most frequently used operation is the clipboard data. In particular, if you write program to develop own editors like notepad, clipboard operation is very common. Java provides Toolkit class which defines the static resources to access the various API to perform operation. getSystemClipboard method in Toolkit class would help you to update the content to clipboard.

This example program would store the simple to text to clipboard and then display from the clipboard. Lets look at the example.

ClipboardExample.java

[code lang=”java”]
package javabeat.net.core;

import java.awt.Toolkit;
import java.awt.datatransfer.Clipboard;
import java.awt.datatransfer.DataFlavor;
import java.awt.datatransfer.StringSelection;
import java.awt.datatransfer.UnsupportedFlavorException;
import java.io.IOException;

public class ClipboardExample {
public static void main(String[] args) {
String str = "Java Clipboard Example Text!!";

Toolkit toolkit = Toolkit.getDefaultToolkit();
Clipboard clipboard = toolkit.getSystemClipboard();
StringSelection strSel = new StringSelection(str);
clipboard.setContents(strSel, null);
String result = null;
try{
result = (String) clipboard.getData(DataFlavor.stringFlavor);
}catch (IOException exception){
exception.printStackTrace();
}catch (UnsupportedFlavorException exception){
exception.printStackTrace();
}
System.out.println("Clipboard Text :" + result);
}
}
[/code]

Output…

[code]
Clipboard Text :Java Clipboard Example Text!!
[/code]

If you are working on system programming in Java, it is very common to run the processes for starting some external applications. Runtime class defines a method to execute the external applications. This example shows how to open another eclipse instance from the Java program. This example opens the eclipse IDE, and the closes the same process after 25 seconds. Lets look at the example.
RunAnotherApplicationExample.java

[code lang=”java”]
package javabeat.net.core;

import java.io.IOException;

public class RunAnotherApplicationExample {
public static void main(String[] args) {
try {
System.out.println("Opening notepad");
Runtime runTime = Runtime.getRuntime();

//Opens your eclipse ide
System.out.println("Opening Eclipse");
Process process = runTime.exec("eclipse");
try {
Thread.sleep(25000);
} catch (InterruptedException e) {
e.printStackTrace();
}
System.out.println("Closing Eclipse");
//Closing your eclipse ide
process.destroy();
} catch (IOException e) {
e.printStackTrace();
}
}
}
[/code]

Java’s System class maintains a property object which contains the various details of the current user, Java version, operating system, etc. These are predefined values and can be easily accessed by calling the System class level methods. This utility is very useful to get the native operating system details. Lets look at the below example which lists all the default values stored with the System class properties object. Note that programmer can set the own properties values by overriding the existing values.

SystemPropertiesExample.java

[code lang=”java”]
package javabeat.net.core;

public class SystemPropertiesExample {
public static void main(String[] args) {
System.out.println("File Separator : " + System.getProperty("file.separator"));
System.out.println("Class Path : "+System.getProperty("java.class.path"));
System.out.println("Java Home : "+System.getProperty("java.home"));
System.out.println("Java Vendor Name : "+System.getProperty("java.vendor"));
System.out.println("Java Vendor URL :"+System.getProperty("java.vendor.url"));
System.out.println("Installed Java Version :"+System.getProperty("java.version"));
System.out.println("Line Separator : "+System.getProperty("line.separator"));
System.out.println("OS Architecture :"+System.getProperty("os.arch"));
System.out.println("OS Name :"+System.getProperty("os.name"));
System.out.println("OS Version :"+System.getProperty("os.version"));
System.out.println("Path Separator :"+System.getProperty("path.separator"));
System.out.println("User Directory :"+System.getProperty("user.dir"));
System.out.println("User Home :"+System.getProperty("user.home"));
System.out.println("User Name :"+System.getProperty("user.name"));
}
}
[/code]

Output…

[code]
File Separator : /
Class Path : /home/krishna/workspace/Java Project/bin:
Java Home : /usr/lib/jvm/java-6-openjdk-i386/jre
Java Vendor Name : Sun Microsystems Inc.
Java Vendor URL :http://java.sun.com/
Installed Java Version :1.6.0_27
Line Separator :

OS Architecture :i386
OS Name :Linux
OS Version :3.2.0-54-generic
Path Separator ::
User Directory :/home/krishna/workspace/Java Project
User Home :/home/krishna
User Name :krishna
[/code]