Regular Expressions 101

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An explanation of your regex will be automatically generated as you type.
Detailed match information will be displayed here automatically.
  • All Tokens
  • Common Tokens
  • General Tokens
  • Anchors
  • Meta Sequences
  • Quantifiers
  • Group Constructs
  • Character Classes
  • Flags/Modifiers
  • Substitution
  • A single character of: a, b or c
    [abc]
  • A character except: a, b or c
    [^abc]
  • A character in the range: a-z
    [a-z]
  • A character not in the range: a-z
    [^a-z]
  • A character in the range: a-z or A-Z
    [a-zA-Z]
  • Any single character
    .
  • Alternate - match either a or b
    a|b
  • Any whitespace character
    \s
  • Any non-whitespace character
    \S
  • Any digit
    \d
  • Any non-digit
    \D
  • Any word character
    \w
  • Any non-word character
    \W
  • Non-capturing group
    (?:...)
  • Capturing group
    (...)
  • Zero or one of a
    a?
  • Zero or more of a
    a*
  • One or more of a
    a+
  • Exactly 3 of a
    a{3}
  • 3 or more of a
    a{3,}
  • Between 3 and 6 of a
    a{3,6}
  • Start of string
    ^
  • End of string
    $
  • A word boundary
    \b
  • Non-word boundary
    \B

Regular Expression
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Test String

Substitution
Processing...

Code Generator

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Generated Code

import java.util.regex.Matcher; import java.util.regex.Pattern; public class Example { public static void main(String[] args) { final String regex = "(?m)^(?:(?:(?&V_Obj)|(?&V_Ary))|(?<Invalid>(?&Er_Obj)|(?&Er_Ary))(*SKIP)(*FAIL))(?(DEFINE)(?<Sep_Ary>(?:,(?!\\s*[\\}\\]])|(?=\\s*[\\]])))(?<Sep_Obj>(?:,(?!\\s*[\\}\\]])|(?=\\s*[\\}])))(?<Er_Obj>(?>\\{(?:\\s*(?&Str)(?:\\s*:(?:\\s*(?:(?&Er_Value)|(?<Er_Ary>\\[(?:\\s*(?:(?&Er_Value)|(?&Er_Ary)|(?&Er_Obj))(?:\\s*(?&Sep_Ary)|(*ACCEPT)))*(?:\\s*\\]|(*ACCEPT)))|(?&Er_Obj))(?:\\s*(?&Sep_Obj)|(*ACCEPT))|(*ACCEPT))|(*ACCEPT)))*(?:\\s*\\}|(*ACCEPT))))(?<Er_Value>(?>(?&Numb)|(?>true|false|null)|(?&Str)))(?<Str>(?>\"[^\\\\\"]*(?:\\\\[\\s\\S][^\\\\\"]*)*\"))(?<Numb>(?>[+-]?(?:\\d+(?:\\.\\d*)?|\\.\\d+)(?:[eE][+-]?\\d+)?|(?:[eE][+-]?\\d+)))(?<V_KeyVal>(?>\\s*(?&Str)\\s*:\\s*(?&V_Value)\\s*))(?<V_Value>(?>(?&Numb)|(?>true|false|null)|(?&Str)|(?&V_Obj)|(?&V_Ary)))(?<V_Ary>\\[(?>\\s*(?&V_Value)\\s*(?&Sep_Ary))*\\s*\\])(?<V_Obj>\\{(?>\\s*(?&V_KeyVal)\\s*(?&Sep_Obj))*\\s*\\}))"; final String string = "\n" + "================================\n" + "Valid JSON :\n" + "=================================\n\n" + "1. Nested Objects and Arrays (Company Structure)\n" + "This example demonstrates a company structure with departments, each containing a list of employees.\n\n" + "{\n" + " \"company\": \"Global Solutions Inc.\",\n" + " \"headquarters\": {\n" + " \"city\": \"New York\",\n" + " \"state\": \"NY\",\n" + " \"zip\": \"10001\"\n" + " },\n" + " \"departments\": [\n" + " {\n" + " \"name\": \"Engineering\",\n" + " \"manager\": {\n" + " \"id\": \"ENG001\",\n" + " \"firstName\": \"Alice\",\n" + " \"lastName\": \"Johnson\"\n" + " },\n" + " \"employees\": [\n" + " {\n" + " \"id\": \"EMP001\",\n" + " \"firstName\": \"Bob\",\n" + " \"lastName\": \"Williams\",\n" + " \"position\": \"Software Engineer\",\n" + " \"skills\": [\"Python\", \"Java\", \"SQL\"]\n" + " },\n" + " {\n" + " \"id\": \"EMP002\",\n" + " \"firstName\": \"Charlie\",\n" + " \"lastName\": \"Davis\",\n" + " \"position\": \"DevOps Engineer\",\n" + " \"skills\": [\"AWS\", \"Docker\", \"Kubernetes\"]\n" + " }\n" + " ]\n" + " },\n" + " {\n" + " \"name\": \"Marketing\",\n" + " \"manager\": {\n" + " \"id\": \"MKT001\",\n" + " \"firstName\": \"David\",\n" + " \"lastName\": \"Miller\"\n" + " },\n" + " \"employees\": [\n" + " {\n" + " \"id\": \"EMP003\",\n" + " \"firstName\": \"Eve\",\n" + " \"lastName\": \"Taylor\",\n" + " \"position\": \"Marketing Specialist\",\n" + " \"skills\": [\"SEO\", \"Content Creation\"]\n" + " }\n" + " ]\n" + " }\n" + " ],\n" + " \"projects\": [\n" + " {\n" + " \"projectId\": \"PROJ101\",\n" + " \"projectName\": \"New Product Launch\",\n" + " \"status\": \"In Progress\",\n" + " \"teamMembers\": [\"EMP001\", \"EMP003\"]\n" + " }\n" + " ]\n" + "}\n\n\n" + "2. GeoJSON Feature Collection (Geospatial Data)\n" + "This example uses the GeoJSON standard to represent a collection of geographic features.\n\n" + "{\n" + " \"type\": \"FeatureCollection\",\n" + " \"features\": [\n" + " {\n" + " \"type\": \"Feature\",\n" + " \"properties\": {\n" + " \"name\": \"Eiffel Tower\",\n" + " \"country\": \"France\",\n" + " \"city\": \"Paris\"\n" + " },\n" + " \"geometry\": {\n" + " \"type\": \"Point\",\n" + " \"coordinates\": [2.2945, 48.8584]\n" + " }\n" + " },\n" + " {\n" + " \"type\": \"Feature\",\n" + " \"properties\": {\n" + " \"name\": \"Central Park\",\n" + " \"country\": \"USA\",\n" + " \"city\": \"New York\"\n" + " },\n" + " \"geometry\": {\n" + " \"type\": \"Polygon\",\n" + " \"coordinates\": [\n" + " [\n" + " [-73.981, 40.768],\n" + " [-73.958, 40.796],\n" + " [-73.949, 40.793],\n" + " [-73.981, 40.768]\n" + " ]\n" + " ]\n" + " }\n" + " }\n" + " ]\n" + "}\n\n\n" + "3. Product Catalog with Variations (E-commerce)\n" + "This JSON structure represents a product catalog with various product details and variations.\n\n" + "{\n" + " \"catalogId\": \"CAT001\",\n" + " \"products\": [\n" + " {\n" + " \"productId\": \"PROD001\",\n" + " \"name\": \"T-Shirt\",\n" + " \"description\": \"Comfortable cotton t-shirt.\",\n" + " \"price\": 19.99,\n" + " \"availableSizes\": [\"S\", \"M\", \"L\", \"XL\"],\n" + " \"colors\": [\n" + " {\n" + " \"name\": \"Red\",\n" + " \"hexCode\": \"#FF0000\",\n" + " \"stock\": { \"S\": 10, \"M\": 15, \"L\": 8, \"XL\": 5 }\n" + " },\n" + " {\n" + " \"name\": \"Blue\",\n" + " \"hexCode\": \"#0000FF\",\n" + " \"stock\": { \"S\": 12, \"M\": 20, \"L\": 10, \"XL\": 7 }\n" + " }\n" + " ],\n" + " \"reviews\": [\n" + " {\n" + " \"userId\": \"USER001\",\n" + " \"rating\": 5,\n" + " \"comment\": \"Great quality and fit!\"\n" + " },\n" + " {\n" + " \"userId\": \"USER002\",\n" + " \"rating\": 4,\n" + " \"comment\": \"Good t-shirt, a bit pricey.\"\n" + " }\n" + " ]\n" + " },\n" + " {\n" + " \"productId\": \"PROD002\",\n" + " \"name\": \"Jeans\",\n" + " \"description\": \"Classic denim jeans.\",\n" + " \"price\": 49.99,\n" + " \"availableSizes\": [\"28\", \"30\", \"32\", \"34\"],\n" + " \"colors\": [\n" + " {\n" + " \"name\": \"Indigo\",\n" + " \"hexCode\": \"#4B0082\",\n" + " \"stock\": { \"28\": 7, \"30\": 10, \"32\": 12, \"34\": 8 }\n" + " }\n" + " ]\n" + " }\n" + " ]\n" + "}\n\n\n" + "=========================\n" + "Invalid JSON :\n" + "=========================\n\n" + "These examples illustrate various ways in which a JSON file can be considered invalid according to the JSON specification. Developers often encounter these types of errors during data serialization or parsing.\n\n" + " -----------------\n" + "1. Missing Double Quotes around Keys:\n" + "Code\n\n" + "{\n" + " name: \"Alice\",\n" + " \"age\": 30,\n" + " \"city\": \"New York\"\n" + "}\n\n" + "Invalidity: The key name is not enclosed in double quotes, which is a requirement in JSON. \n\n" + " -----------------\n" + "2. Trailing Commas in Objects or Arrays:\n" + "Code\n\n" + "{\n" + " \"item1\": \"value1\",\n" + " \"item2\": \"value2\",\n" + "}\n\n" + " Invalidity: There is a trailing comma after the last key-value pair in the object. \n\n" + "Code\n\n" + "[\n" + " \"element1\",\n" + " \"element2\",\n" + "]\n\n" + "Invalidity: There is a trailing comma after the last element in the array. \n\n" + " -----------------\n" + "3. Incorrect Data Types or Values:\n" + "Code\n\n" + "{\n" + " \"product\": \"Laptop\",\n" + " \"price\": $1200.00,\n" + " \"available\": True\n" + "}\n\n" + "Invalidity: The price value $1200.00 is not a valid JSON number (currency symbols are not allowed). The available value True is not a valid JSON boolean (must be lowercase true or false). \n\n" + " -----------------\n" + "4. Mismatched Braces or Brackets:\n" + "Code\n\n" + "{\n" + " \"user\": {\n" + " \"id\": 123,\n" + " \"name\": \"Bob\",\n" + " \"details\": [\n" + " \"email\": \"bob@example.com\"\n" + " }\n" + " ]\n" + "}\n\n" + "Invalidity: The details array contains an object that is closed with a } instead of a ], and the array itself is closed with a ] after the object, leading to a structural mismatch. \n\n" + " -----------------\n" + "5. Unescaped Characters within Strings:\n" + "Code\n\n" + "{\n" + " \"message\": \"He said, \"Hello!\"\"\n" + "}\n\n" + " Invalidity: The double quotes within the string \"Hello!\" are not escaped, causing a syntax error. They should be \\\"Hello!\\\". \n\n" + " -----------------\n" + "6. Comments within JSON:\n" + "Code\n\n" + "{\n" + " // This is a comment\n" + " \"data\": \"some value\"\n" + "}\n\n" + " Invalidity: JSON does not support comments. \n\n" + " -----------------\n" + "7. Missing Colons or Values in Key-Value Pairs:\n" + "Code\n\n" + "{\n" + " \"key1\": \"value1\",\n" + " \"key2\"\n" + " \"key3\": \"value3\"\n" + "}\n\n" + " Invalidity: The key2 entry is missing a colon and a value. \n\n" + " -----------------\n" + "8. Invalid JSON Structure (e.g., array with object syntax):\n" + "Code\n\n" + "[\n" + " \"item1\": \"value1\",\n" + " \"item2\": \"value2\"\n" + "]\n\n" + "Invalidity: An array cannot contain key-value pairs; it should contain elements directly. \n\n\n" + "{\n" + " \"key1\" : \"value1\",\n" + " \"key2\" \"lk\"\n" + "}\n" + " -----------------\n\n" + "{\n" + " \"key1\" : \"value1\"\n" + " \"key2\" \"lk\"\n" + "}\n" + " -----------------\n\n" + "{\n" + " \"key1\" : \"value1\",\n" + " \"key2\" \"lk\"\n" + "}\n" + " -----------------\n\n" + "{\n" + " \"key1\" : \"value1\",\n" + " \"key2\" : mj\n" + "}\n" + " -----------------\n\n" + "{\n" + " \"key1\" : \"value1\",\n" + " \"key2\" : \"mj\n" + "}\n" + " -----------------\n\n" + "{\n" + " \"key1\" : \"value1\",\n" + " \"hhh\" : [ \n" + " { \n" + " \"key0\" : [{\"MMM\" : \"a\"}, \"b\",\"c\"],\n" + " \"key2\" : \"mj\",\n" + " \"key3\" :\n" + " [ \n" + " -----------------\n\n" + "[\n" + " \"mn\" \n" + " {\"MMM\" : a\"} ,\n" + " \"b\" , \"c\"\n" + "]\n\n"; final String subst = "$1 ERROR_here>> "; final Pattern pattern = Pattern.compile(regex); final Matcher matcher = pattern.matcher(string); // The substituted value will be contained in the result variable final String result = matcher.replaceAll(subst); System.out.println("Substitution result: " + result); } }

Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Java, please visit: https://docs.oracle.com/javase/7/docs/api/java/util/regex/Pattern.html