java.util
Class Scanner

java.lang.Object   
  java.util.Scanner

All Implemented Interfaces:

Iterator <String >

public final class Scanner
extends Object   
implements Iterator   <String   >

A simple text scanner which can parse primitive types and strings using regular expressions.

A Scanner breaks its input into tokens using a delimiter pattern, which by default matches whitespace. The resulting tokens may then be converted into values of different types using the various next methods.

For example, this code allows a user to read a number from System.in:

     Scanner sc = new Scanner(System.in);
     int i = sc.nextInt();
 

As another example, this code allows long types to be assigned from entries in a file myNumbers:

      Scanner sc = new Scanner(new File("myNumbers"));
      while (sc.hasNextLong()) {
          long aLong = sc.nextLong();
      }

The scanner can also use delimiters other than whitespace. This example reads several items in from a string:

     String input = "1 fish 2 fish red fish blue fish";
     Scanner s = new Scanner(input).useDelimiter("\\s*fish\\s*");
     System.out.println(s.nextInt());
     System.out.println(s.nextInt());
     System.out.println(s.next());
     System.out.println(s.next());
     s.close(); 

prints the following output:

     1
     2
     red
     blue 

The same output can be generated with this code, which uses a regular expression to parse all four tokens at once:

     String input = "1 fish 2 fish red fish blue fish";
     Scanner s = new Scanner(input);
     s.findInLine("(\\d+) fish (\\d+) fish (\\w+) fish (\\w+)");
     MatchResult result = s.match();
     for (int i=1; i<=result.groupCount(); i++)
         System.out.println(result.group(i);
     s.close(); 

The default whitespace delimiter used by a scanner is as recognized by Character .isWhitespace .

A scanning operation may block waiting for input.

The next() and hasNext() methods and their primitive-type companion methods (such as nextInt() and hasNextInt() ) first skip any input that matches the delimiter pattern, and then attempt to return the next token. Both hasNext and next methods may block waiting for further input. Whether a hasNext method blocks has no connection to whether or not its associated next method will block.

The findInLine(java.lang.String) , findWithinHorizon(java.lang.String, int) , and skip(java.util.regex.Pattern) methods operate independently of the delimiter pattern. These methods will attempt to match the specified pattern with no regard to delimiters in the input and thus can be used in special circumstances where delimiters are not relevant. These methods may block waiting for more input.

When a scanner throws an InputMismatchException , the scanner will not pass the token that caused the exception, so that it may be retrieved or skipped via some other method.

Depending upon the type of delimiting pattern, empty tokens may be returned. For example, the pattern "\\s+" will return no empty tokens since it matches multiple instances of the delimiter. The delimiting pattern "\\s" could return empty tokens since it only passes one space at a time.

A scanner can read text from any object which implements the Readable interface. If an invocation of the underlying readable's Readable.read(java.nio.CharBuffer) method throws an IOException then the scanner assumes that the end of the input has been reached. The most recent IOException thrown by the underlying readable can be retrieved via the ioException() method.

When a Scanner is closed, it will close its input source if the source implements the Closeable interface.

A Scanner is not safe for multithreaded use without external synchronization.

Unless otherwise mentioned, passing a null parameter into any method of a Scanner will cause a NullPointerException to be thrown.

A scanner will default to interpreting numbers as decimal unless a different radix has been set by using the useRadix(int) method.

Localized numbers

An instance of this class is capable of scanning numbers in the standard formats as well as in the formats of the scanner's locale. A scanner's initial locale is the value returned by the Locale.getDefault() method; it may be changed via the useLocale(java.util.Locale) method.

The localized formats are defined in terms of the following parameters, which for a particular locale are taken from that locale's DecimalFormat object, df, and its and DecimalFormatSymbols object, dfs.

LocalGroupSeparator	The character used to separate thousands groups, i.e., dfs.getGroupingSeparator()
LocalDecimalSeparator	The character used for the decimal point, i.e., dfs.getDecimalSeparator()
LocalPositivePrefix	The string that appears before a positive number (may be empty), i.e., df.getPositivePrefix()
LocalPositiveSuffix	The string that appears after a positive number (may be empty), i.e., df.getPositiveSuffix()
LocalNegativePrefix	The string that appears before a negative number (may be empty), i.e., df.getNegativePrefix()
LocalNegativeSuffix	The string that appears after a negative number (may be empty), i.e., df.getNegativeSuffix()
LocalNaN	The string that represents not-a-number for floating-point values, i.e., dfs.getInfinity()
LocalInfinity	The string that represents infinity for floating-point values, i.e., dfs.getInfinity()

Number syntax

The strings that can be parsed as numbers by an instance of this class are specified in terms of the following regular-expression grammar, where Rmax is the highest digit in the radix being used (for example, Rmax is 9 in base 10).

NonASCIIDigit ::

= A non-ASCII character c for which Character.isDigit (c) returns true

Non0Digit ::

= [1-Rmax] | NonASCIIDigit

Digit ::

= [0-Rmax] | NonASCIIDigit

GroupedNumeral ::

= (	Non0Digit Digit? Digit?
	( LocalGroupSeparator Digit Digit Digit )+ )

Numeral ::

= ( ( Digit+ ) | GroupedNumeral )

Integer ::

= ( [-+]? ( Numeral ) )

| LocalPositivePrefix Numeral LocalPositiveSuffix

| LocalNegativePrefix Numeral LocalNegativeSuffix

DecimalNumeral ::

= Numeral

| Numeral LocalDecimalSeparator Digit*

| LocalDecimalSeparator Digit+

Exponent ::

= ( [eE] [+-]? Digit+ )

Decimal ::

= ( [-+]? DecimalNumeral Exponent? )

| LocalPositivePrefix DecimalNumeral LocalPositiveSuffix Exponent?

| LocalNegativePrefix DecimalNumeral LocalNegativeSuffix Exponent?

HexFloat ::

= [-+]? 0[xX][0-9a-fA-F]*\.[0-9a-fA-F]+ ([pP][-+]?[0-9]+)?

NonNumber ::

= NaN | LocalNan | Infinity | LocalInfinity

SignedNonNumber ::

= ( [-+]? NonNumber )

| LocalPositivePrefix NonNumber LocalPositiveSuffix

| LocalNegativePrefix NonNumber LocalNegativeSuffix

Float ::

= Decimal

| HexFloat

| SignedNonNumber

Whitespace is not significant in the above regular expressions.

Since:

1.5

Constructor Summary

Scanner (File source)
Constructs a new Scanner that produces values scanned from the specified file.

Scanner (File source, String charsetName)
Constructs a new Scanner that produces values scanned from the specified file.

Scanner (InputStream source)
Constructs a new Scanner that produces values scanned from the specified input stream.

Scanner (InputStream source, String charsetName)
Constructs a new Scanner that produces values scanned from the specified input stream.

Scanner (Readable source)
Constructs a new Scanner that produces values scanned from the specified source.

Scanner (ReadableByteChannel source)
Constructs a new Scanner that produces values scanned from the specified channel.

Scanner (ReadableByteChannel source, String charsetName)
Constructs a new Scanner that produces values scanned from the specified channel.

Scanner (String source)
Constructs a new Scanner that produces values scanned from the specified string.

Method Summary

void	close () Closes this scanner.
Pattern	delimiter () Returns the Pattern this Scanner is currently using to match delimiters.
String	findInLine (Pattern pattern) Attempts to find the next occurrence of the specified pattern ignoring delimiters.
String	findInLine (String pattern) Attempts to find the next occurrence of a pattern constructed from the specified string, ignoring delimiters.
String	findWithinHorizon (Pattern pattern, int horizon) Attempts to find the next occurrence of the specified pattern.
String	findWithinHorizon (String pattern, int horizon) Attempts to find the next occurrence of a pattern constructed from the specified string, ignoring delimiters.
boolean	hasNext () Returns true if this scanner has another token in its input.
boolean	hasNext (Pattern pattern) Returns true if the next complete token matches the specified pattern.
boolean	hasNext (String pattern) Returns true if the next token matches the pattern constructed from the specified string.
boolean	hasNextBigDecimal () Returns true if the next token in this scanner's input can be interpreted as a BigDecimal using the nextBigDecimal() method.
boolean	hasNextBigInteger () Returns true if the next token in this scanner's input can be interpreted as a BigInteger in the default radix using the nextBigInteger() method.
boolean	hasNextBigInteger (int radix) Returns true if the next token in this scanner's input can be interpreted as a BigInteger in the specified radix using the nextBigInteger() method.
boolean	hasNextBoolean () Returns true if the next token in this scanner's input can be interpreted as a boolean value using a case insensitive pattern created from the string "true|false".
boolean	hasNextByte () Returns true if the next token in this scanner's input can be interpreted as a byte value in the default radix using the nextByte() method.
boolean	hasNextByte (int radix) Returns true if the next token in this scanner's input can be interpreted as a byte value in the specified radix using the nextByte() method.
boolean	hasNextDouble () Returns true if the next token in this scanner's input can be interpreted as a double value using the nextDouble() method.
boolean	hasNextFloat () Returns true if the next token in this scanner's input can be interpreted as a float value using the nextFloat() method.
boolean	hasNextInt () Returns true if the next token in this scanner's input can be interpreted as an int value in the default radix using the nextInt() method.
boolean	hasNextInt (int radix) Returns true if the next token in this scanner's input can be interpreted as an int value in the specified radix using the nextInt() method.
boolean	hasNextLine () Returns true if there is another line in the input of this scanner.
boolean	hasNextLong () Returns true if the next token in this scanner's input can be interpreted as a long value in the default radix using the nextLong() method.
boolean	hasNextLong (int radix) Returns true if the next token in this scanner's input can be interpreted as a long value in the specified radix using the nextLong() method.
boolean	hasNextShort () Returns true if the next token in this scanner's input can be interpreted as a short value in the default radix using the nextShort() method.
boolean	hasNextShort (int radix) Returns true if the next token in this scanner's input can be interpreted as a short value in the specified radix using the nextShort() method.
IOException	ioException () Returns the IOException last thrown by this Scanner's underlying Readable.
Locale	locale () Returns this scanner's locale.
MatchResult	match () Returns the match result of the last scanning operation performed by this scanner.
String	next () Finds and returns the next complete token from this scanner.
String	next (Pattern pattern) Returns the next token if it matches the specified pattern.
String	next (String pattern) Returns the next token if it matches the pattern constructed from the specified string.
BigDecimal	nextBigDecimal () Scans the next token of the input as a BigDecimal .
BigInteger	nextBigInteger () Scans the next token of the input as a BigInteger .
BigInteger	nextBigInteger (int radix) Scans the next token of the input as a BigInteger .
boolean	nextBoolean () Scans the next token of the input into a boolean value and returns that value.
byte	nextByte () Scans the next token of the input as a byte.
byte	nextByte (int radix) Scans the next token of the input as a byte.
double	nextDouble () Scans the next token of the input as a double.
float	nextFloat () Scans the next token of the input as a float.
int	nextInt () Scans the next token of the input as an int.
int	nextInt (int radix) Scans the next token of the input as an int.
String	nextLine () Advances this scanner past the current line and returns the input that was skipped.
long	nextLong () Scans the next token of the input as a long.
long	nextLong (int radix) Scans the next token of the input as a long.
short	nextShort () Scans the next token of the input as a short.
short	nextShort (int radix) Scans the next token of the input as a short.
int	radix () Returns this scanner's default radix.
void	remove () The remove operation is not supported by this implementation of Iterator.
Scanner	skip (Pattern pattern) Skips input that matches the specified pattern, ignoring delimiters.
Scanner	skip (String pattern) Skips input that matches a pattern constructed from the specified string.
String	toString () Returns the string representation of this Scanner.
Scanner	useDelimiter (Pattern pattern) Sets this scanner's delimiting pattern to the specified pattern.
Scanner	useDelimiter (String pattern) Sets this scanner's delimiting pattern to a pattern constructed from the specified String.
Scanner	useLocale (Locale