Scanner is the complement of Formatter and reads formatted input. Scanner can be used to read input from the console, a file, a string, or any source.
The Scanner Constructors
Scanner(File from) throws FileNotFoundException
Creates a Scanner that uses the file specified by from as a source for input.
Scanner(File from, String charset) throws FileNotFoundException
Creates a Scanner that uses the file specified by from with the encoding specified by charset as a source for input.
Scanner(InputStream from)
Creates a Scanner that uses the stream specified by from as a source for input.
Scanner(InputStream from, String charset)
Creates a Scanner that uses the stream specified by from with the encoding specified by charset as a source for input.
Scanner(Readable from)
Creates a Scanner that uses the Readable object specified by from as a source for input.
Scanner (ReadableByteChannel from)
Creates a Scanner that uses the ReadableByteChannel specified by from as a source for input.
Scanner(ReadableByteChannel from, String charset)
Creates a Scanner that uses the ReadableByteChannel specified by from with the encoding specified by charset as a source for input.
Scanner(String from)
Creates a Scanner that uses the string specified by from as a source for input.
The following code creates a Scanner that reads the file Test.txt:
FileReader fin = new FileReader("Test.txt");
Scanner src = new Scanner(fin);
FileReader implements the Readable interface. Thus, the call to the constructor resolves to Scanner(Readable).
This next line creates a Scanner that reads from standard input, which is the keyboard by default:
Scanner conin = new Scanner(System.in);
System.in is an object of type InputStream. Thus, the call to the constructor maps to Scanner(InputStream).
The next sequence creates a Scanner that reads from a string.
String instr = "1 1.23 this is a test.";
Scanner conin = new Scanner(instr);