Examples of java.util.Scanner

java.util.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 {@link java.lang.Character}. {@link java.lang.Character#isWhitespace(char) isWhitespace}. The {@link #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 {@link #next} and {@link #hasNext} methods and their primitive-type companion methods (such as {@link #nextInt} and {@link #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 {@link #findInLine}, {@link #findWithinHorizon}, and {@link #skip}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 {@link 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 {@link java.lang.Readable} interface. If an invocation of the underlyingreadable's {@link java.lang.Readable#read} method throws an {@link java.io.IOException} then the scanner assumes that the end of the inputhas been reached. The most recent IOException thrown by the underlying readable can be retrieved via the {@link #ioException} method.

When a Scanner is closed, it will close its input source if the source implements the {@link java.io.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 {@link #useRadix} method. The{@link #reset} method will reset the value of the scanner's radix to10 regardless of whether it was previously changed.

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 {@link java.util.Locale#getDefault} method; it may be changed via the {@link #useLocale} method. The {@link #reset} method will reset the value of thescanner'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 {@link java.text.DecimalFormat DecimalFormat} object, df, and its and{@link java.text.DecimalFormatSymbols DecimalFormatSymbols} object,dfs.

LocalGroupSeparator   The character used to separate thousands groups, i.e., dfs. {@link java.text.DecimalFormatSymbols#getGroupingSeparator getGroupingSeparator()}

LocalDecimalSeparator   The character used for the decimal point, i.e., dfs. {@link java.text.DecimalFormatSymbols#getDecimalSeparator getDecimalSeparator()}

LocalPositivePrefix   The string that appears before a positive number (may be empty), i.e., df. {@link java.text.DecimalFormat#getPositivePrefix getPositivePrefix()}

LocalPositiveSuffix   The string that appears after a positive number (may be empty), i.e., df. {@link java.text.DecimalFormat#getPositiveSuffix getPositiveSuffix()}

LocalNegativePrefix   The string that appears before a negative number (may be empty), i.e., df. {@link java.text.DecimalFormat#getNegativePrefix getNegativePrefix()}

LocalNegativeSuffix   The string that appears after a negative number (may be empty), i.e., df. {@link java.text.DecimalFormat#getNegativeSuffix getNegativeSuffix()}

LocalNaN   The string that represents not-a-number for floating-point values, i.e., dfs. {@link java.text.DecimalFormatSymbols#getNaN getNaN()}

LocalInfinity   The string that represents infinity for floating-point values, i.e., dfs. {@link java.text.DecimalFormatSymbols#getInfinity 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 {@link java.lang.Character#isDigit 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. @version 1.27, 06/28/06 @since 1.5

      File file = res.getFile();
      if (file.getName().endsWith("stdout")) {
        // there has to be some content in stdout file
        assertThat("there has to be content in stdout file", file.length(), greaterThan(0l));
        if (file.getName().equals("Container.stdout")) {
          Scanner scanner = new Scanner(file);
          String content = scanner.useDelimiter("\\A").next();
          scanner.close();
          // check that we have a simple timestamp
          assertThat("content doesn't look like timestamp", content.length(), greaterThan(10));
          assertThat("content doesn't look like timestamp", content.length(), lessThan(40));
        }
      } else if (file.getName().endsWith("stderr")) {
        String content = "";
        if (file.length() > 0) {
          Scanner scanner = new Scanner(file);
          content = scanner.useDelimiter("\\A").next();
          scanner.close();
        }
        if (content.contains("Unable to load realm info from SCDynamicStore")) {
          // due to OS X giving 'Unable to load realm info from SCDynamicStore' errors we allow 100 bytes here
          assertThat("stderr file is not empty: " + content, file.length(), lessThan(100l));
        } else {

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    initDefaultTable();
    configureExport(new ExportConf.Builder("xml").header(true).build());
    processExport(new XmlExport());
    
    // The header must exist
    Scanner scanner = new Scanner(new String(baos.toByteArray()));
    String firstLine = scanner.nextLine();
    
    assertThat(firstLine).contains("<?xml version=\"1.0\"?>");
    assertThat(firstLine).contains("<persons>");
    assertThat(firstLine).contains("</persons>");
    assertThat(firstLine).contains("<person id=\"1\" firstName=\"Selma\" lastName=\"Maldonado\" city=\"\" mail=\"venenatis@Duisvolutpat.com\"></person><person id=\"2\" firstName=\"Vanna\" lastName=\"Salas\" city=\"Denny\" mail=\"bibendum.fermentum.metus@ante.ca\"></person>");

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    initDefaultTable();
    configureExport(new ExportConf.Builder("csv").header(true).build());
    processExport(new CsvExport());
    
    // The header must exist
    String firstLine = new Scanner(new String(baos.toByteArray())).nextLine();
    assertThat(firstLine).contains("Id;FirstName;LastName;City;Mail");
    
    // There must be as many line as entries in Mock.persons (+1 for the header row)
    assertThat(new String(baos.toByteArray()).split("\n")).hasSize(Mock.persons.size() + 1);
  }

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    initDefaultTable();
    configureExport(new ExportConf.Builder("csv").header(false).build());
    processExport(new CsvExport());
    
    // The header must exist
    String firstLine = new Scanner(new String(baos.toByteArray())).nextLine();
    assertThat(firstLine).doesNotContain("Id;FirstName;LastName;City;Mail");
    
    // There must be as many line as entries in Mock.persons (+1 for the header row)
    assertThat(new String(baos.toByteArray()).split("\n")).hasSize(Mock.persons.size());
  }

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    initTable();
    configureExport(new ExportConf.Builder("csv").header(false).build());
    processExport(new CsvExport());
    
    String firstLine = new Scanner(new String(baos.toByteArray())).nextLine();
    assertThat(StringUtils.countOccurrencesOf(firstLine, ";")).isEqualTo(4);
  }

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     * @param analogy_file a {@code String} containing the absolute path to the analogy file. 
     */
    public void loadAnalogiesFromFile(String analogy_file) {


            try {
                Scanner sc = new Scanner(new File(analogy_file));
                while (sc.hasNext()) {
                    String analogy = sc.next();
                    if (!isAnalogyFormat(analogy)) {
                        System.err.println("\"" + analogy + "\" not in proper format.");
                        continue;
                    }
                    String analogy_pair[] = analogy.split(":");
                    String A = analogy_pair[0];
                    String B = analogy_pair[1];


                    //1. Find alternates for A and B
                    Synset[] A_prime = findAlternatives(A);
                    Synset[] B_prime = findAlternatives(B);
                    
                    //2. Filter phrases
                    ArrayList<String> tmp = new ArrayList<String>(filterPhrases(INDEX_DIR,A,B,A_prime,B_prime));
                    filtered_phrases.addAll(tmp);
                    original_to_alternates.put(A+":"+B, tmp);
                }
                sc.close();
            } catch (Exception e) {
                System.err.println("Could not read file.");
            }
    }

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        for (int i = 0; i < files.length; i++) {
            File f = files[i];
            if (f.isDirectory()) {
                pattern_set.addAll(searchDirectoryForPattern(f, A, B));
            } else if (f.getName().endsWith(".txt")) {
                Scanner sc = new Scanner(f);
                while (sc.hasNext()) {
                    if (A.equals(sc.next())) {
                        String pattern = "";
                        int count = 0;
                        while (count <= MAX_INTER && sc.hasNext()) { 
                            String curr = sc.next();
                            if (count >= MIN_INTER && B.equals(curr)) {
                                //add the String onto a Set of Strings containing the patterns
                                //System.err.println("adding pattern: " + pattern);
                                pattern_set.add(pattern);
                                break;

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        for (int i = 0; i < files.length; i++) {
            File f = files[i];
            if (f.isDirectory()) {
                total += countWildcardPhraseFrequencies(f, pattern);
            } else if (f.getName().endsWith(".txt")) {
                Scanner sc = new Scanner(f);
                while (sc.hasNext()) {
                    String line = sc.nextLine();
                    if (line.matches(pattern)) {
                        total++;
                    }
                }
            }

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     *
     * @see #computeCosineSimilarity(String,Matrix)
     **/
    public void evaluateAnalogies(Matrix projection, String inputFileName, String outputFileName) {
            try {
                Scanner sc = new Scanner(new File(inputFileName));
                PrintStream out = new PrintStream(new FileOutputStream(outputFileName));
                while (sc.hasNext()) {
                    String analogy = sc.next();
                    if (!isAnalogyFormat(analogy,true)) {
                        System.err.println("\"" + analogy + "\" not in proper format.");
                        continue;
                    }
                    double cosineVal = computeCosineSimilarity(analogy, projection); //does the actual cosine value calculations and comparisons
                    out.println(analogy + " = " + cosineVal);
                }
                sc.close();
                out.close();
            } catch (Exception e) {
                System.err.println("Could not read file.");
            }
    }

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     *
     * @see #computeCosineSimilarity(String,Matrix)
     **/
    public void evaluateAnalogies(Matrix projection) {
            try {
                Scanner sc = new Scanner(System.in);
                while (sc.hasNext()) {
                    String analogy = sc.next();
                    if (!isAnalogyFormat(analogy,true)) {
                        System.err.println("\"" + analogy + "\" not in proper format.");
                        continue;
                    }
                    double cosineVal = computeCosineSimilarity(analogy, projection); //does the actual cosine value calculations and comparisons
                    System.out.println(analogy + " = " + cosineVal);
                }
                sc.close();
            } catch (Exception e) {
                System.err.println("Could not read file.");
            }
    }

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