Java The Complete Reference, Seventh Edition

540 Part II: The Java Library

Scanner

Scanneris the complement ofFormatter. Added by JDK 5,Scannerreads formatted input

and converts it into its binary form. Although it has always been possible to read formatted

input, it required more effort than most programmers would prefer. Because of the addition

ofScanner, it is now easy to read all types of numeric values, strings, and other types of

data, whether it comes from a disk file, the keyboard, or another source.

Scannercan be used to read input from the console, a file, a string, or any source that

implements theReadableinterface orReadableByteChannel. For example, you can use

Scannerto read a number from the keyboard and assign its value to a variable. As you will

see, given its power,Scanneris surprisingly easy to use.

The Scanner Constructors

Scannerdefines the constructors shown in Table 18-14. In general, aScannercan be

created for aString, anInputStream, aFile, or any object that implements theReadable

orReadableByteChannelinterfaces. Here are some examples.

The following sequence creates aScannerthat reads the fileTest.txt:

FileReader fin = new FileReader("Test.txt");

Scanner src = new Scanner(fin);

This works becauseFileReaderimplements theReadableinterface. Thus, the call to the

constructor resolves toScanner(Readable).

Method Description

Scanner(Filefrom)

throws FileNotFoundException

Creates aScannerthat uses the file specified by

fromas a source for input.

Scanner(Filefrom, Stringcharset)

throws FileNotFoundException

Creates aScannerthat uses the file specified byfrom

with the encoding specified bycharsetas a source for

input.

Scanner(InputStreamfrom) Creates aScannerthat uses the stream specified

byfromas a source for input.

Scanner(InputStreamfrom, Stringcharset) Creates aScannerthat uses the stream specified

byfromwith the encoding specified bycharsetas

a source for input.

Scanner(Readablefrom) Creates aScannerthat uses theReadableobject

specified byfromas a source for input.

Scanner (ReadableByteChannelfrom) Creates aScannerthat uses theReadableByteChannel

specified byfromas a source for input.

Scanner(ReadableByteChannelfrom,

Stringcharset)

Creates aScannerthat uses theReadableByteChannel

specified byfromwith the encoding specified bycharset

as a source for input.

Scanner(Stringfrom) Creates aScannerthat uses the string specified by

fromas a source for input.

TABLE 18-14 TheScannerConstructors