Java : Pattern (regex) with Examples

Pattern (Java SE 18 & JDK 18) API Examples.
You will find code examples on most Pattern methods.

Summary

A compiled representation of a regular expression.

Class diagram

final var pattern = Pattern.compile("a+bc");
final var matchPredicate = pattern.asMatchPredicate();

System.out.println(matchPredicate.test("abc")); // true
System.out.println(matchPredicate.test("aaaabc")); // true

System.out.println(matchPredicate.test("ab")); // false
System.out.println(matchPredicate.test("abcD")); // false
System.out.println(matchPredicate.test("Zabc")); // false

final var pattern = Pattern.compile("a+bc");
final var predicate = pattern.asPredicate();

System.out.println(predicate.test("abc")); // true
System.out.println(predicate.test("aaaabc")); // true

System.out.println(predicate.test("ab")); // false
System.out.println(predicate.test("abcD")); // true
System.out.println(predicate.test("Zabc")); // true

final var pattern = Pattern.compile("a+bc");
final var matcher = pattern.matcher("xyz aaaabc 012");

if (matcher.find()) {
    System.out.println(matcher.group()); // "aaaabc"
}

Fields

static final int CANON_EQ

Enables canonical equivalence.
...
The expression "a\u030A", for example, will match the string "\u00E5" when this flag is specified.

final var regex = "a\u030A";
System.out.println(regex); // å

final var input = "\u00E5";
System.out.println(input); // å

{
    final var pattern = Pattern.compile(regex, Pattern.CANON_EQ);
    final var matchPredicate = pattern.asMatchPredicate();

    System.out.println(matchPredicate.test(input)); // true
}

{
    final var pattern = Pattern.compile(regex);
    final var matchPredicate = pattern.asMatchPredicate();

    System.out.println(matchPredicate.test(input)); // false
}

static final int CASE_INSENSITIVE

Enables case-insensitive matching.

final var regex = "abc";
final var input = "ABC";

{
    final var pattern = Pattern.compile(regex, Pattern.CASE_INSENSITIVE);
    final var matchPredicate = pattern.asMatchPredicate();

    System.out.println(matchPredicate.test(input)); // true
}

{
    final var pattern = Pattern.compile(regex);
    final var matchPredicate = pattern.asMatchPredicate();

    System.out.println(matchPredicate.test(input)); // false
}

static final int COMMENTS

Permits whitespace and comments in pattern.

final var regex = "a b c # xyz";
final var input = "abc";

{
    final var pattern = Pattern.compile(regex, Pattern.COMMENTS);
    final var matchPredicate = pattern.asMatchPredicate();

    System.out.println(matchPredicate.test(input)); // true
}

{
    final var pattern = Pattern.compile(regex);
    final var matchPredicate = pattern.asMatchPredicate();

    System.out.println(matchPredicate.test(input)); // false
}

static final int DOTALL

Enables dotall mode.

final var regex = "abc..yz";
final var input = "abc\nxyz";

{
    final var pattern = Pattern.compile(regex, Pattern.DOTALL);
    final var matchPredicate = pattern.asMatchPredicate();

    System.out.println(matchPredicate.test(input)); // true
}

{
    final var pattern = Pattern.compile(regex);
    final var matchPredicate = pattern.asMatchPredicate();

    System.out.println(matchPredicate.test(input)); // false
}

static final int LITERAL

Enables literal parsing of the pattern.

final var regex = "abc+";
final var input1 = "abc+";
final var input2 = "abccc";

{
    final var pattern = Pattern.compile(regex, Pattern.LITERAL);
    final var matchPredicate = pattern.asMatchPredicate();

    System.out.println(matchPredicate.test(input1)); // true
    System.out.println(matchPredicate.test(input2)); // false
}

{
    final var pattern = Pattern.compile(regex);
    final var matchPredicate = pattern.asMatchPredicate();

    System.out.println(matchPredicate.test(input1)); // false
    System.out.println(matchPredicate.test(input2)); // true
}

static final int MULTILINE

Enables multiline mode.

final var regex = "^abc$";
final var input1 = """
        012
        abc
        xyz
        """;
final var input2 = "abc";

{
    final var pattern = Pattern.compile(regex, Pattern.MULTILINE);
    final var predicate = pattern.asPredicate();

    System.out.println(predicate.test(input1)); // true
    System.out.println(predicate.test(input2)); // true
}

{
    final var pattern = Pattern.compile(regex);
    final var predicate = pattern.asPredicate();

    System.out.println(predicate.test(input1)); // false
    System.out.println(predicate.test(input2)); // true
}

static final int UNICODE_CASE

Enables Unicode-aware case folding.

// Double-byte character set.
final var regex = "ａｂｃ";
final var input = "ＡＢＣ";

{
    final var pattern = Pattern.compile(regex, Pattern.UNICODE_CASE | Pattern.CASE_INSENSITIVE);
    final var matchPredicate = pattern.asMatchPredicate();

    System.out.println(matchPredicate.test(input)); // true
}

{
    final var pattern = Pattern.compile(regex, Pattern.CASE_INSENSITIVE);
    final var matchPredicate = pattern.asMatchPredicate();

    System.out.println(matchPredicate.test(input)); // false
}

static final int UNICODE_CHARACTER_CLASS

Enables the Unicode version of Predefined character classes and POSIX character classes.

final var regex = "\\p{Lower}+";

final var input1 = "abc";

// Double-byte character set.
final var input2 = "ａｂｃ";

{
    final var pattern = Pattern.compile(regex, Pattern.UNICODE_CHARACTER_CLASS);
    final var matchPredicate = pattern.asMatchPredicate();

    System.out.println(matchPredicate.test(input1)); // true
    System.out.println(matchPredicate.test(input2)); // true
}

{
    final var pattern = Pattern.compile(regex);
    final var matchPredicate = pattern.asMatchPredicate();

    System.out.println(matchPredicate.test(input1)); // true
    System.out.println(matchPredicate.test(input2)); // false
}

static final int UNIX_LINES

Enables Unix lines mode.

final var regex = "^abc$";

final var input1 = "abc\r\nxyz";
final var input2 = "abc\nxyz";
final var input3 = "abc\rxyz";

{
    final var pattern = Pattern.compile(regex, Pattern.UNIX_LINES | Pattern.MULTILINE);
    final var predicate = pattern.asPredicate();

    System.out.println(predicate.test(input1)); // false
    System.out.println(predicate.test(input2)); // true
    System.out.println(predicate.test(input3)); // false
}

{
    final var pattern = Pattern.compile(regex, Pattern.MULTILINE);
    final var predicate = pattern.asPredicate();

    System.out.println(predicate.test(input1)); // true
    System.out.println(predicate.test(input2)); // true
    System.out.println(predicate.test(input3)); // true
}

Methods

Predicate<String> asMatchPredicate ()

Creates a predicate that tests if this pattern matches a given input string.

final var pattern = Pattern.compile("a+bc");

final var matchPredicate = pattern.asMatchPredicate();
final var predicate = pattern.asPredicate();

System.out.println(matchPredicate.test("aaabc")); // true
System.out.println(predicate.test("aaabc")); // true

System.out.println(matchPredicate.test("012 abc xyz")); // false
System.out.println(predicate.test("012 abc xyz")); // true

Predicate<String> asPredicate ()

Creates a predicate that tests if this pattern is found in a given input string.

Please see asMatchPredicate().

static Pattern compile (String regex)

Compiles the given regular expression into a pattern.

final var pattern = Pattern.compile("a+bc");
final var matchPredicate = pattern.asMatchPredicate();

System.out.println(matchPredicate.test("abc")); // true
System.out.println(matchPredicate.test("aaaabc")); // true
System.out.println(matchPredicate.test("bc")); // false

static Pattern compile (String regex, int flags)

Compiles the given regular expression into a pattern with the given flags.

final var pattern = Pattern.compile("abc", Pattern.CASE_INSENSITIVE);
final var matchPredicate = pattern.asMatchPredicate();

System.out.println(matchPredicate.test("abc")); // true
System.out.println(matchPredicate.test("ABC")); // true

final var pattern = Pattern.compile("abc");
final var matchPredicate = pattern.asMatchPredicate();

System.out.println(matchPredicate.test("abc")); // true
System.out.println(matchPredicate.test("ABC")); // false

int flags ()

Returns this pattern's match flags.

final var pattern = Pattern.compile("abc", Pattern.LITERAL);

System.out.println("0x%x".formatted(Pattern.LITERAL)); // 0x10
System.out.println("0x%x".formatted(pattern.flags())); // 0x10

final var pattern = Pattern.compile("abc", Pattern.UNICODE_CASE | Pattern.CASE_INSENSITIVE);

System.out.println("0x%x".formatted(Pattern.UNICODE_CASE)); // 0x40
System.out.println("0x%x".formatted(Pattern.CASE_INSENSITIVE)); // 0x2
System.out.println("0x%x".formatted(pattern.flags())); // 0x42

Matcher matcher (CharSequence input)

Creates a matcher that will match the given input against this pattern.

final var pattern = Pattern.compile("a+bc");
final var matcher = pattern.matcher("zyz aaaabc 012");

if (matcher.find()) {
    System.out.println(matcher.group()); // "aaaabc"
}

static boolean matches (String regex, CharSequence input)

Compiles the given regular expression and attempts to match the given input against it.

System.out.println(Pattern.matches("a+bc", "aaabc")); // true
System.out.println(Pattern.matches("a+bc", "aaabc xyz")); // false

System.out.println(Pattern.matches("[a-z]+", "abcxyz")); // true
System.out.println(Pattern.matches("[a-z]+", "0123")); // false

String pattern ()

Returns the regular expression from which this pattern was compiled.

final var pattern = Pattern.compile("a+bc");
System.out.println(pattern.pattern()); // "a+bc"

final var pattern = Pattern.compile("[a-z]+");
System.out.println(pattern.pattern()); // "[a-z]+"

static String quote (String s)

Returns a literal pattern String for the specified String.

final var regex = "a+bc";

final var quote = Pattern.quote(regex);
System.out.println(quote); // "\Qa+bc\E"

final var pattern = Pattern.compile(quote);
final var matchPredicate = pattern.asMatchPredicate();

System.out.println(matchPredicate.test("a+bc")); // true
System.out.println(matchPredicate.test("aaabc")); // false

String[] split (CharSequence input)

Splits the given input sequence around matches of this pattern.

final var input = "boo:and:foo";

final var pattern = Pattern.compile(":");
final var ret = pattern.split(input);
System.out.println(Arrays.toString(ret)); // [boo, and, foo]

final var input = "boo:and:foo";
final var pattern = Pattern.compile("o");

final var ret = pattern.split(input);
System.out.println(Arrays.toString(ret)); // [b, , :and:f]

String[] split (CharSequence input, int limit)

Splits the given input sequence around matches of this pattern.

final var input = "boo:and:foo";
final var pattern = Pattern.compile(":");

final var ret1 = pattern.split(input, 2);
System.out.println(Arrays.toString(ret1)); // [boo, and:foo]

final var ret2 = pattern.split(input, 5);
System.out.println(Arrays.toString(ret2)); // [boo, and, foo]

final var ret3 = pattern.split(input, -2);
System.out.println(Arrays.toString(ret3)); // [boo, and, foo]

final var input = "boo:and:foo";
final var pattern = Pattern.compile("o");

final var ret1 = pattern.split(input, 5);
System.out.println(Arrays.toString(ret1)); // [b, , :and:f, , ]

final var ret2 = pattern.split(input, -2);
System.out.println(Arrays.toString(ret2)); // [b, , :and:f, , ]

final var ret3 = pattern.split(input, 0);
System.out.println(Arrays.toString(ret3)); // [b, , :and:f]

Stream<String> splitAsStream (CharSequence input)

Creates a stream from the given input sequence around matches of this pattern.

final var input = "boo:and:foo";
final var pattern = Pattern.compile(":");
final var stream = pattern.splitAsStream(input);

stream.forEach(s -> {
    System.out.println(s);
});

// Result
// ↓
// "boo"
// "and"
// "foo"

final var input = "boo:and:foo";
final var pattern = Pattern.compile("o");
final var stream = pattern.splitAsStream(input);

stream.forEach(s -> {
    System.out.println(s);
});

// Result
// ↓
// "b"
// ""
// ":and:f"

String toString ()

Returns the string representation of this pattern.

final var pattern = Pattern.compile("a+bc");
final var str = pattern.toString();
System.out.println(str); // "a+bc"

final var pattern = Pattern.compile("[a-z]+");
final var str = pattern.toString();
System.out.println(str); // "[a-z]+"

API Examples
- Matcher
- MatchResult

Java : Pattern (regex) with Examples

Summary

Fields

static final int CANON_EQ

static final int CASE_INSENSITIVE

static final int COMMENTS

static final int DOTALL

static final int LITERAL

static final int MULTILINE

static final int UNICODE_CASE

static final int UNICODE_CHARACTER_CLASS

static final int UNIX_LINES

Methods

Predicate<String> asMatchPredicate ()

Predicate<String> asPredicate ()

static Pattern compile (String regex)

static Pattern compile (String regex, int flags)

int flags ()

Matcher matcher (CharSequence input)

static boolean matches (String regex, CharSequence input)

String pattern ()

static String quote (String s)

String[] split (CharSequence input)

String[] split (CharSequence input, int limit)

Stream<String> splitAsStream (CharSequence input)

String toString ()

Related posts