Basics of System class

According to the specifications of Java Programming Language, the facilities provided by this class are :

a) Standard input, output and error streams
b) Access to the defined "properties"
c) means of loading files and libraries and
d) utility method for quickly copying a portion of an array.

The most common use we do in our programs is to put debug statements on console, using:

System.out.println(....).

Being the static class, the call to an object/method can be made as System.methodName or System.objectName and not by making the object of this class. In System.out.println: "out" is an object of PrintStream and println is the method of that class. One of the important feature to note here is that the "out" and "err" objects are of PrintStream which is the sub-class of OutputStream. But the "in" is the object of the InputStream. The advantages of PrintStream object will be done sometime later.

The next important feature but least commonly used is to determine the System properties. There is a native method called initProperties(). This method guarantees that the following properties are defined always:

	Key		Description of Associated Value
java.version	Java Runtime Environment version
java.vendor	Java Runtime Environment vendor
java.vendor.url	Java vendor URL
java.home	Java installation directory
java.vm.specification.version	Java Virtual Machine specification version
java.vm.specification.vendor	Java Virtual Machine specification vendor
java.vm.specification.name	Java Virtual Machine specification name
java.vm.version	Java Virtual Machine implementation version
java.vm.vendor	Java Virtual Machine implementation vendor
java.vm.name	Java Virtual Machine implementation name
java.specification.version	Java Runtime Environment specification version
java.specification.vendor	Java Runtime Environment specification vendor
java.specification.name	Java Runtime Environment specification name
java.class.version	Java class format version number
java.class.path	Java class path
java.library.path	List of paths to search when loading libraries
java.io.tmpdir	Default temp file path
java.compiler	Name of JIT compiler to use
java.ext.dirs	Path of extension directory or directories
os.name	Operating system name
os.arch	Operating system architecture
os.version	Operating system version
file.separator	File separator ("/" on UNIX)
path.separator	Path separator (":" on UNIX)
line.separator	Line separator ("\n" on UNIX)
user.name	User's account name
user.home	User's home directory
user.dir	User's current working directory

Multiple paths in a system property value are separated by the path separator character of the platform.

So, System.getProperty("line.separator") will return the line separator based on which OS ..etc etc.

This class is also used to load the files and libraries, using methods load(fileNameWithFullPathAsString) and loadLibrary(libNameAsString). The standard strategy is to call like:

static { System.loadLibrary("LibFile");

This gets loaded as the class is intialized. These methods can be also called as:

Runtime.getRuntime().loadLibrary(name)

Finally, there is a utility method to copy an array beginnin from the specified array
position to a specified position. The signature of the methods is as:

public static void arraycopy(Object src, int srcPos, Object dest,
int destPos, int length)

The src and dest object here can be same.

Finally, the method exit(int i): a nonzero status code indicates abnormal termination.