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String interning
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<p>In computer science, string interning is a method of storing only one copy of each distinct <a href="/facts/String_(computer_science)/4ChJu5WS">string</a> value, which must be <a href="/facts/Immutable_object/Gsoq1bba">immutable</a>. Interning strings makes some string processing tasks more time-efficient or space-efficient at the cost of requiring more time when the string is created or interned. The distinct values are stored in a string intern pool. </p><p>The single copy of each string is called its <i>intern</i> and is typically looked up by a method of the string class, for example String.intern() in <a href="/facts/Java_(programming_language)/9ScgFyAL">Java</a>. All compile-time constant strings in Java are automatically interned using this method. </p><p>String interning is supported by some modern <a href="/facts/Object-oriented/TxNMEcao">object-oriented</a> <a href="/facts/Programming_language/cWTYbgWa">programming languages</a>, including Java, <a href="/facts/Python_(programming_language)/YbuGqofa">Python</a>, <a href="/facts/PHP/vU6YRJX0">PHP</a> (since 5.4), <a href="/facts/Lua_(programming_language)/xkBCgta0">Lua</a> and <a href="/facts/List_of_CLI_languages/LnpaWLBK">.NET languages</a>. <a href="/facts/Lisp_(programming_language)/xJHA3CrX">Lisp</a>, <a href="/facts/Scheme_(programming_language)/0aGdf3SC">Scheme</a>, <a href="/facts/Julia_(programming_language)/AoB0PJ9C">Julia</a>, <a href="/facts/Ruby_(programming_language)/BeYSaPSR">Ruby</a> and <a href="/facts/Smalltalk/Ru2UPVDE">Smalltalk</a> are among the languages with a <a href="/facts/Symbol_(programming)/Hy33Tz7o">symbol</a> type that are basically interned strings. The library of the <a href="/facts/Standard_ML_of_New_Jersey/5WUYMHsD">Standard ML of New Jersey</a> contains an atom type that does the same thing. <a href="/facts/Objective-C/5mM557BW">Objective-C</a>'s selectors, which are mainly used as method names, are interned strings. </p><p>Objects other than strings can be interned. For example, in Java, when primitive values are <a href="/facts/Object_type_(object-oriented_programming)/a49SD1kP">boxed</a> into a <a href="/facts/Primitive_wrapper_class/5uDUQKHH">wrapper object</a>, certain values (any boolean, any byte, any char from 0 to 127, and any short or int between −128 and 127) are interned, and any two boxing conversions of one of these values are guaranteed to result in the same object. </p>