Often, a program requires the access to system resources like properties, the current time, standard input and output streams or Your program can use these resources directly from current runtime environment but your program would only be able to run in the environment for which it was written for. Each time you want the program to run in a new environment, you should have to "port" the program by rewriting the system-dependent sections of the code.

• The standard input, output and error streams
• The system properties
• The garbage collection
• loading the dynamic libraries
• finally the miscellany, including getting the current time, copying arrays, using the security manager and exiting the runtime environment