java.lang.Objectjava.util.Scanner
public final class Scanner
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 . The reset() method will reset the value of the scanner's delimiter to the default whitespace delimiter regardless of whether it was previously changed.
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. The
reset()
method will reset the value of the scanner's radix to 10 regardless of whether it was previously changed.
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
reset()
method will reset the value of the scanner's locale to the initial locale regardless of whether it was previously changed.
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
.
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).
Localized numbers
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.
getNaN()
LocalInfinity
The string that represents infinity for floating-point values,
i.e.,
dfs.
getInfinity()
Number syntax
NonASCIIDigit :: | = A non-ASCII character c for which Character.isDigit (c) returns true | ||||
Non0Digit :: | = [1- Rmax ] | NonASCIIDigit | ||||
Digit :: | = [0- Rmax ] | NonASCIIDigit | ||||
GroupedNumeral :: |
|
||||
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.
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 |
reset
() Resets this scanner. |
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
locale) Sets this scanner's locale to the specified locale. |
Scanner |
useRadix
(int radix) Sets this scanner's default radix to the specified radix. |
Methods inherited from class java.lang. Object |
---|
clone , equals , finalize , getClass , hashCode , notify , notifyAll , wait , wait , wait |
Constructor Detail |
---|
public Scanner(Readable source)
public Scanner(InputStream source)
public Scanner(InputStream source, String charsetName)
public Scanner(File source) throws FileNotFoundException
public Scanner(File source, String charsetName) throws FileNotFoundException
public Scanner(String source)
public Scanner(ReadableByteChannel source)
public Scanner(ReadableByteChannel source, String charsetName)
Method Detail |
---|
public void close()
If this scanner has not yet been closed then if its underlying readable also implements the Closeable interface then the readable's close method will be invoked. If this scanner is already closed then invoking this method will have no effect.
Attempting to perform search operations after a scanner has been closed will result in an IllegalStateException .
public IOException ioException()
public Pattern delimiter()
public Scanner useDelimiter(Pattern pattern)
public Scanner useDelimiter(String pattern)
An invocation of this method of the form useDelimiter(pattern) behaves in exactly the same way as the invocation useDelimiter(Pattern.compile(pattern)) .
Invoking the reset() method will set the scanner's delimiter to the default .
public Locale locale()
A scanner's locale affects many elements of its default primitive matching regular expressions; see localized numbers above.
public Scanner useLocale(Locale locale)
A scanner's locale affects many elements of its default primitive matching regular expressions; see localized numbers above.
Invoking the reset() method will set the scanner's locale to the initial locale .
public int radix()
A scanner's radix affects elements of its default number matching regular expressions; see localized numbers above.
public Scanner useRadix(int radix)
A scanner's radix affects elements of its default number matching regular expressions; see localized numbers above.
If the radix is less than Character.MIN_RADIX or greater than Character.MAX_RADIX, then an IllegalArgumentException is thrown.
Invoking the
reset()
#reset)
method will set the scanner's radix to 10.
public MatchResult match()
The various nextmethods of Scanner make a match result available if they complete without throwing an exception. For instance, after an invocation of the nextInt() method that returned an int, this method returns a MatchResult for the search of the Integer regular expression defined above. Similarly the findInLine(java.lang.String) , findWithinHorizon(java.lang.String, int) , and skip(java.util.regex.Pattern) methods will make a match available if they succeed.
public String toString()
Returns the string representation of this Scanner. The string representation of a Scanner contains information that may be useful for debugging. The exact format is unspecified.
public boolean hasNext()
public String next()
public void remove()
public boolean hasNext(String pattern)
An invocation of this method of the form hasNext(pattern) behaves in exactly the same way as the invocation hasNext(Pattern.compile(pattern)) .
public String next(String pattern)
An invocation of this method of the form next(pattern) behaves in exactly the same way as the invocation next(Pattern.compile(pattern)) .
public boolean hasNext(Pattern pattern)
public String next(Pattern pattern)
public boolean hasNextLine()
public String nextLine()
Since this method continues to search through the input looking for a line separator, it may buffer all of the input searching for the line to skip if no line separators are present.
public String findInLine(String pattern)
An invocation of this method of the form findInLine(pattern) behaves in exactly the same way as the invocation findInLine(Pattern.compile(pattern)) .
public String findInLine(Pattern pattern)
Since this method continues to search through the input looking for the specified pattern, it may buffer all of the input searching for the desired token if no line separators are present.
public String findWithinHorizon(String pattern, int horizon)
An invocation of this method of the form findWithinHorizon(pattern) behaves in exactly the same way as the invocation findWithinHorizon(Pattern.compile(pattern, horizon)) .
public String findWithinHorizon(Pattern pattern, int horizon)
This method searches through the input up to the specified search horizon, ignoring delimiters. If the pattern is found the scanner advances past the input that matched and returns the string that matched the pattern. If no such pattern is detected then the null is returned and the scanner's position remains unchanged. This method may block waiting for input that matches the pattern.
A scanner will never search more than horizon code points beyond its current position. Note that a match may be clipped by the horizon; that is, an arbitrary match result may have been different if the horizon had been larger. The scanner treats the horizon as a transparent, non-anchoring bound (see Matcher.useTransparentBounds(boolean) and Matcher.useAnchoringBounds(boolean) ).
If horizon is 0, then the horizon is ignored and this method continues to search through the input looking for the specified pattern without bound. In this case it may buffer all of the input searching for the pattern.
If horizon is negative, then an IllegalArgumentException is thrown.
public Scanner skip(Pattern pattern)
If a match to the specified pattern is not found at the current position, then no input is skipped and a NoSuchElementException is thrown.
Since this method seeks to match the specified pattern starting at the scanner's current position, patterns that can match a lot of input (".*", for example) may cause the scanner to buffer a large amount of input.
Note that it is possible to skip something without risking a NoSuchElementException by using a pattern that can match nothing, e.g., sc.skip("[ \t]*").
public Scanner skip(String pattern)
An invocation of this method of the form skip(pattern) behaves in exactly the same way as the invocation skip(Pattern.compile(pattern)) .
public boolean hasNextBoolean()
public boolean nextBoolean()
public boolean hasNextByte()
public boolean hasNextByte(int radix)
public byte nextByte()
An invocation of this method of the form nextByte() behaves in exactly the same way as the invocation nextByte(radix) , where radix is the default radix of this scanner.
public byte nextByte(int radix)
If the next token matches the Integer regular expression defined above then the token is converted into a byte value as if by removing all locale specific prefixes, group separators, and locale specific suffixes, then mapping non-ASCII digits into ASCII digits via Character.digit , prepending a negative sign (-) if the locale specific negative prefixes and suffixes were present, and passing the resulting string to Byte.parseByte with the specified radix.
public boolean hasNextShort()
public boolean hasNextShort(int radix)
public short nextShort()
An invocation of this method of the form nextShort() behaves in exactly the same way as the invocation nextShort(radix) , where radix is the default radix of this scanner.
public short nextShort(int radix)
If the next token matches the Integer regular expression defined above then the token is converted into a short value as if by removing all locale specific prefixes, group separators, and locale specific suffixes, then mapping non-ASCII digits into ASCII digits via Character.digit , prepending a negative sign (-) if the locale specific negative prefixes and suffixes were present, and passing the resulting string to Short.parseShort with the specified radix.
public boolean hasNextInt()
public boolean hasNextInt(int radix)
public int nextInt()
An invocation of this method of the form nextInt() behaves in exactly the same way as the invocation nextInt(radix) , where radix is the default radix of this scanner.
public int nextInt(int radix)
If the next token matches the Integer regular expression defined above then the token is converted into an int value as if by removing all locale specific prefixes, group separators, and locale specific suffixes, then mapping non-ASCII digits into ASCII digits via Character.digit , prepending a negative sign (-) if the locale specific negative prefixes and suffixes were present, and passing the resulting string to Integer.parseInt with the specified radix.
public boolean hasNextLong()
public boolean hasNextLong(int radix)
public long nextLong()
An invocation of this method of the form nextLong() behaves in exactly the same way as the invocation nextLong(radix) , where radix is the default radix of this scanner.
public long nextLong(int radix)
If the next token matches the Integer regular expression defined above then the token is converted into a long value as if by removing all locale specific prefixes, group separators, and locale specific suffixes, then mapping non-ASCII digits into ASCII digits via Character.digit , prepending a negative sign (-) if the locale specific negative prefixes and suffixes were present, and passing the resulting string to Long.parseLong with the specified radix.
public boolean hasNextFloat()
public float nextFloat()
If the next token matches the Float regular expression defined above then the token is converted into a float value as if by removing all locale specific prefixes, group separators, and locale specific suffixes, then mapping non-ASCII digits into ASCII digits via Character.digit , prepending a negative sign (-) if the locale specific negative prefixes and suffixes were present, and passing the resulting string to Float.parseFloat . If the token matches the localized NaN or infinity strings, then either "Nan" or "Infinity" is passed to Float.parseFloat as appropriate.
public boolean hasNextDouble()
public double nextDouble()
If the next token matches the Float regular expression defined above then the token is converted into a double value as if by removing all locale specific prefixes, group separators, and locale specific suffixes, then mapping non-ASCII digits into ASCII digits via Character.digit , prepending a negative sign (-) if the locale specific negative prefixes and suffixes were present, and passing the resulting string to Double.parseDouble . If the token matches the localized NaN or infinity strings, then either "Nan" or "Infinity" is passed to Double.parseDouble as appropriate.
public boolean hasNextBigInteger()
public boolean hasNextBigInteger(int radix)
public BigInteger nextBigInteger()
An invocation of this method of the form nextBigInteger() behaves in exactly the same way as the invocation nextBigInteger(radix) , where radix is the default radix of this scanner.
public BigInteger nextBigInteger(int radix)
If the next token matches the Integer regular expression defined above then the token is converted into a BigInteger value as if by removing all group separators, mapping non-ASCII digits into ASCII digits via the Character.digit , and passing the resulting string to the BigInteger(String, int) constructor with the specified radix.
public boolean hasNextBigDecimal()
public BigDecimal nextBigDecimal()
If the next token matches the Decimal regular expression defined above then the token is converted into a BigDecimal value as if by removing all group separators, mapping non-ASCII digits into ASCII digits via the Character.digit , and passing the resulting string to the BigDecimal(String) constructor.
public Scanner reset()
Resetting a scanner discards all of its explicit state information which may have been changed by invocations of useDelimiter(java.util.regex.Pattern) , useLocale(java.util.Locale) , or useRadix(int) .
An invocation of this method of the form scanner.reset() behaves in exactly the same way as the invocation
scanner.useDelimiter("\\p{javaWhitespace}+") .useLocale(Locale.getDefault()) .useRadix(10);