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Not matching a given string

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To match something that does not contain a given string, one can use negative lookahead:

Regex syntax: (?!string-to-not-match)

Example: 

//not matching "popcorn"
String regexString = "^(?!popcorn).*$";
System.out.println("[popcorn] " + ("popcorn".matches(regexString) ? "matched!" : "nope!"));
System.out.println("[unicorn] " + ("unicorn".matches(regexString) ? "matched!" : "nope!"));

Output: 

[popcorn] nope!
[unicorn] matched!
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Regular Expressions:
* Regular Expressions
* Using capture groups
* Using regex with custom behaviour by compiling the Pattern with flags
* Escape Characters
* Not matching a given string
* Matching with a regex literal.
* Matching a backslash
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0 Inheritance
1 Getting started with Java
2 Streams
3 Exceptions
4 Collections
5 Lambda Expressions
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118 Pitfalls - threads and concurrency
119 Splitting a string into fixed length parts
120 Pitfalls - nulls and NullPointerException
121 SecurityManager
122 JNDI
123 super keyword
124 java.util.Objects class
125 Java command: java and javaw
126 Atomic types
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128 Converting to and from strings
129 sun.misc.Unsafe
130 Java Memory Model
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137 Java Virtual Machine JVM
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142 Java SE 8 Features
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147 Using ThreadPoolExecutor in multi-threaded applications
148 Java Editions, versions, releases and distributions
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152 Generating Java Code
153 JShell
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176 Enum starting with a number
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180 StringBuffer
181 Choosing Collections
182 C++ Comparison
183 CompletableFuture
184 Contributors