Standard Input/Output provided by System class
The Java language provides access to standard I/O through the
System class, implementing following three files:
public static InputStream in
public static PrintStream out
public static PrintStream err
 
 
public static InputStream in
 
    System.in implements the standard input stream as an instance of
    InputStream class.
    The standard input file (stdin) is the keyboard.
 
public static PrintStream out 
 
    System.out implements the standard output stream as an instance of
    OutputStream class.
    The standard output (stdout) is usually the terminal screen.
 
public static PrintStream err
 
    System.err implements the standard error stream as an instance of
    OutputStream class.
    The standard error (sterr) is usually the terminal screen.

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