System class

Some methods below: getProperty(...), arrayCopy(...)

■ This class creates the System.in, System.out, and System.err streams.

String getProperty(...) method

■ System.getProperty(“user.dir”) returns the current directory.

■ Other property keys obtainable are:

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.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

void arrayCopy( src[ ], srcIndex, dst[ ], dstIndex, len ) method

■ Copies a len number of elements from the source array, beginning at the srcIndex position, to the dstIndex position of the destination array.

■ This snippet copies the three elements 1 2 3 from the first array, which are located at index zero, into the second array, to reside in place of the second array’s e f g, which are located starting at index 4.

String[ ] a1 = {"1","2","3","4","5","6","7","8","9"};

String[ ] a2 = {"a","b","c","d","e","f","g","h","i" };

System.arraycopy(a1, 0, a2, 4, 3 );

List aList = Arrays.asList(a1) ;

System.out.println(aList);

List bList = Arrays.asList(a2) ;

System.out.println(bList);

■ This code shifts all the elements of the array to the right by two positions, printing a b a b c d e f g.

Notice how the first two shifted positions retain their original values, and how the shifted-out positions on the far right simply lose their old values. The original array length is not changed. i.e.

String[ ] a2 = {"a","b","c","d","e","f","g","h","i" };

System.out.println(a2.length);

System.arraycopy(a2, 0, a2, 2, a2.length-2 );

List bList = Arrays.asList(a2) ;

System.out.println(bList);