BUILD ROBUST PORTABLE APPLICATIONS BY USING SYSTEM PROPERTIES
Most developers would like their applications to run in as many 
different environments as possible but don't have the time or resources 
to do extensive testing across different platforms. One way to minimize 
the potential for problems on different operating systems is to use the 
properties available through the System class.

The System class contains several property methods that provide 
information about the runtime environment for Java applications and 
idiosyncrasies of the underlying operating system. The following class 
will print out a complete list of all the available properties:

import java.util.*; 
 
public class SysProps 
{ 
   public static void main(String[] args)  
   { 
      Enumeration sysProps = System.getProperties().propertyNames(); 
      while(sysProps.hasMoreElements()) 
      { 
         String propName = (String)sysProps.nextElement(); 
         System.out.println(propName+" : 
"+System.getProperty(propName)); 
      } 
   } 
 
}

For example, to parse or create a file or directory path, the character 
used to separate directory or file names can be retrieved from the 
System property "file.separator" as in this code snippet:

String fileNameDelimiter = System.getProperty("file.separator");

On a Windows system, fileNameDelimiter would consist of the backslash 
(\) character, UNIX systems would return the forward slash (/), and 
MacOS systems a colon (:). Rather than hard-coding these values, an 
application can retrieve the property value at runtime and build up or 
parse file paths properly without prior knowledge about the current 
operating system.

Of course, file paths are just a subset of the potential problems 
encountered when running Java applications on multiple platforms, but 
using as much dynamic information as possible about the underlying 
runtime context can help extend the portability of Java applications 
into untested or even unknown environments. System properties are a 
great way to increase portability with a minimum of effort.