Guava: CharMatcher class

By using CharMatcher class, we can represent particular class of characters like digits, white spaces, invisible characters etc.,

How to obtain CharMatcher instance

1.   Using constants

2.   Using methods provided by CharMatcher class

Obtain CharMatcher instance using constants

CharMatcher class provides following constants to obtain CharMatcher instance.

Constant	Description
ANY	Matches any character.
ASCII	Matches any ASCII character
BREAKING_WHITESPACE	Matches a whitespace which can be interpreted as a break between words for formatting purposes
DIGIT	Matches a digit. It matches digits specified by Unicode. http://unicode.org/cldr/utility/list-unicodeset.jsp?a=%5Cp%7Bdigit%7D
INVISIBLE	Match invisible characters like SPACE_SEPARATOR, LINE_SEPARATOR, PARAGRAPH_SEPARATOR.
JAVA_DIGIT	Match a digit as per isDigit function defined in java.lana.Character class.
JAVA_ISO_CONTROL	Matches an ISO control character as specified by isISOControl method of java.lang.Character class.
JAVA_LETTER	Matches a character according to isLetter method of java.lang.Character class.
JAVA_LETTER_OR_DIGIT	Matches a character whether a character is a letter or digit according to sLetterOrDigit method of java.lang.Character class.
JAVA_LOWER_CASE	Matches a lower case character according to isLowerCase method of Character class.
JAVA_UPPER_CASE	Matches a upper case character according to isUpperCase method of Character class.
NONE	Matches no characters
SINGLE_WIDTH	Determines whether a character is single-width.
WHITESPACE	Determines whether a character is whitespace according to the latest Unicode standard.

                 

Using methods provided by CharMatcher class

You can get instance of CharMatcher class by using following methods.

Method	Description
anyOf(final CharSequence sequence)	Returns a char matcher that matches any character present in the given character sequence.
inRange(final char startInclusive, final char endInclusive)	Returns a char matcher that matches any character in a given range (Inclusive).
is(final char match)	Returns a char matcher that matches only one specified character.
isNot(final char match)	Returns a char matcher that matches any character except the one specified.
noneOf(CharSequence sequence)	Returns a char matcher that matches any character not present in the given character sequence.

        

1. Trim characters from beginning and end of string

Following methods are used to trim given characters from beginning and end of the string.

Method	Description
String trimFrom(CharSequence sequence)	Omits all characters that this matcher matches from the beginning and from the end of the string.
String trimLeadingFrom(CharSequence sequence)	Omits all characters that this matcher matches from the beginning and from the end of the string.
String trimTrailingFrom(CharSequence sequence)	Omits all characters that this matcher matches from the end of the string.

import com.google.common.base.CharMatcher;

public class CharMatcherEx {
  public static void main(String args[]) {
    CharMatcher matcher = CharMatcher.DIGIT;

    String sequence = "1234Hello hari123 How are you12233";

    String result1 = matcher.trimFrom(sequence);
    String result2 = matcher.trimLeadingFrom(sequence);
    String result3 = matcher.trimTrailingFrom(sequence);

    System.out.println("result1 = " + result1);
    System.out.println("result2 = " + result2);
    System.out.println("result3 = " + result3);
  }
}

Output

result1 = Hello hari123 How are you
result2 = Hello hari123 How are you12233
result3 = 1234Hello hari123 How are you

2. Remove multiple tabs and consecutive spaces

By using following methods you can remove multiple tabs and spaces.

Method	Description
String collapseFrom(CharSequence sequence, char replacement)	Replace each group of matching characters with given character. Ex: CharMatcher.anyOf("abd").collapseFrom("bbrakadabra", '_'); statement returns “_r_k_r_”
String trimAndCollapseFrom(CharSequence sequence, char replacement)	Replace each group of matching characters with given character, except that groups of matching characters at the start or end of the sequence are removed without replacement. Ex: CharMatcher.anyOf("abd").trimAndCollapseFrom("bbrakadabra", '_'); statement returns “r_k_r”.

import com.google.common.base.CharMatcher;

public class CharMatcherEx {
  public static void main(String args[]) {
    CharMatcher matcher = CharMatcher.WHITESPACE;

    String sequence = "   Hello   How  Are   You   ";

    String result1 = matcher.collapseFrom(sequence, ' ');
    String result2 = matcher.trimAndCollapseFrom(sequence, ' ');

    System.out.println("result1 = " + result1);
    System.out.println("result2 = " + result2);
  }
}

Output

result1 =  Hello How Are You 
result2 = Hello How Are You

3. Get the number of matching characters

“countIn” method is used to get number of matching characters in given sequence.

import com.google.common.base.CharMatcher;

public class CharMatcherEx {
  public static void main(String args[]) {
    CharMatcher matcher = CharMatcher.anyOf("aeiou");

    String sequence = "Hello, How are you";
    int vowels = matcher.countIn(sequence);

    System.out.println("Number of vowels in '" + sequence + "'are "
        + vowels);
  }
}

Output

Number of vowels in 'Hello, How are you'are 7

4. Get index of matching characters

Following methods are used to get the index of matching character.

Method	Description
int indexIn(CharSequence sequence)	Returns the index of first matching character in given input sequence.
int indexIn(CharSequence sequence, int start)	Returns the index of first matching character in given input sequence, from given starting index.
int lastIndexIn(CharSequence sequence)	Returns the index of the last matching character in a character sequence

import com.google.common.base.CharMatcher;

public class CharMatcherEx {
  public static void main(String args[]) {
    CharMatcher matcher = CharMatcher.anyOf("aeiou");

    String sequence = "Hello, How are you";

    int firstIndex = matcher.indexIn(sequence);
    int nextIndex = matcher.indexIn(sequence, firstIndex + 1);
    int lastIndex = matcher.lastIndexIn(sequence);

    System.out.println("First Index is " + firstIndex);
    System.out.println("Next Index is " + nextIndex);
    System.out.println("Last Index is " + lastIndex);
  }
}

Output

First Index is 1
Next Index is 4
Last Index is 17

5. Matches given characters

Method	Description
boolean matches(char c)	Returns true or false value for the given character.
boolean matchesAllOf(CharSequence sequence)	Returns true if a character sequence contains only matching characters.
boolean matchesAnyOf(CharSequence sequence)	Returns true if a character sequence contains at least one matching character.
boolean matchesNoneOf(CharSequence sequence)	Returns true if a character sequence contains no matching characters.

import com.google.common.base.CharMatcher;

public class CharMatcherEx {
  public static void main(String args[]) {
    CharMatcher matcher = CharMatcher.anyOf("aeiou");

    System.out.println("Is matcher matches 'e'" + matcher.matches('e'));
    System.out.println("Is matcher matches all characters 'lru' "
        + matcher.matchesAllOf("lru"));
    System.out.println("Is matcher matches any of 'uvwxyz'"
        + matcher.matchesAnyOf("uvwxyz"));
    System.out.println("Is matcher don't match any of 'vwxyz'"
        + matcher.matchesNoneOf("vwxyz"));
  }
}

Output

Is matcher matches 'e'true
Is matcher matches all characters 'lru' false
Is matcher matches any of 'uvwxyz'true
Is matcher don't match any of 'vwxyz'true

6. Create negative matcher

CharMatcher class provides negate method, which returns a matcher that matches any character not matched by this matcher.

import com.google.common.base.CharMatcher;

public class CharMatcherEx {
  public static void main(String args[]) {
    CharMatcher matcher = CharMatcher.DIGIT;

    int index = matcher.indexIn("12345Hello");
    System.out.println("Index of first digit is " + index);

    matcher = matcher.negate();
    index = matcher.indexIn("12345Hello");
    System.out.println("Index of first character is " + index);
  }
}

Output

Index of first digit is 0
Index of first character is 5

7. Remove matching characters from given string

CharMatcher class provides removeFrom method, which removes all matching characters from given string.

import com.google.common.base.CharMatcher;

public class CharMatcherEx {
  public static void main(String args[]) {
    CharMatcher matcher = CharMatcher.DIGIT;

    String sequence = "12345Hello How1287 are 9886you8";

    String result = matcher.removeFrom(sequence);
    System.out.println(result);
  }
}

Output

Hello How are you

8.Replace matching characters with given string

CharMatcher class provides two forms of replace methods, which replace matching character with some other string/character.

String replaceFrom(CharSequence sequence, CharSequence replacement)

String replaceFrom(CharSequence sequence, char replacement)

import com.google.common.base.CharMatcher;

public class CharMatcherEx {
  public static void main(String args[]) {
    CharMatcher matcher = CharMatcher.anyOf("a");

    String sequence = "abrakadabra";

    String result = matcher.replaceFrom(sequence, "aaa");
    System.out.println(result);
  }
}

Output

aaabraaakaaadaaabraaa

9.Retaing only matching characters

CharMatcher class provides retainFrom method, to retain only matching characters.

import com.google.common.base.CharMatcher;

public class CharMatcherEx {
  public static void main(String args[]) {
    CharMatcher matcher = CharMatcher.anyOf("ab");

    String sequence = "abrakadabra";
    
    String result = matcher.retainFrom(sequence);
    System.out.println(result);
  }
}

Output

abaaaba

10. Logically connect matcher

CharMatcher class provides and, or methods to logically connect more than one matcher.

Method	Description
CharMatcher and(CharMatcher other)	Returns a matcher that matches any character matched by both this matcher and other.
CharMatcher or(CharMatcher other)	Returns a matcher that matches any character matched by either this matcher or other.

import com.google.common.base.CharMatcher;

public class CharMatcherEx {
  public static void main(String args[]) {
    CharMatcher digitMatcher = CharMatcher.anyOf("1234567890ae");
    CharMatcher vowelsMatcher = CharMatcher.anyOf("aeiou");

    CharMatcher andMatcher = digitMatcher.and(vowelsMatcher);
    CharMatcher orMatcher = digitMatcher.or(vowelsMatcher);

    String result1 = andMatcher.removeFrom("12345hfahfashas0909");
    String result2 = orMatcher.removeFrom("12345hfahfashas0909");

    System.out.println(result1);
    System.out.println(result2);
  }
}

Output

12345hfhfshs0909
hfhfshs

11. Match character in given range

CharMatcher class provides inRange method, to match characters in given range.

Following program removes all lower case letters.

import com.google.common.base.CharMatcher;

public class CharMatcherEx {
  public static void main(String args[]) {
    CharMatcher alphaMatcher = CharMatcher.inRange('a', 'z');
    String sequence = "Hello123abceZebra";

    String result = alphaMatcher.removeFrom(sequence);
    System.out.println(result);
  }
}

Output

H123Z

12. Match single character

By using is method of CharMatcher class, you can match exactly one character.

import com.google.common.base.CharMatcher;

public class CharMatcherEx {
  public static void main(String args[]) {
    CharMatcher matcher = CharMatcher.is('p');
    String sequence = "ptrptrptrptrptr";

    System.out.println(matcher.removeFrom(sequence));
    System.out.println(matcher.retainFrom(sequence));
  }
}

Output

trtrtrtrtr
ppppp

13. Match all characters other than one character

CharMatcher class provides isNot method to match all characters, other than given character. It is revers of ‘is’ method.

import com.google.common.base.CharMatcher;

public class CharMatcherEx {
  public static void main(String args[]) {
    CharMatcher matcher = CharMatcher.isNot('p');
    String sequence = "ptrptrptrptrptr";

    System.out.println(matcher.removeFrom(sequence));
    System.out.println(matcher.retainFrom(sequence));
  }
}

Output

ppppp
trtrtrtrtr

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