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59-579: The Kotlin programming language is named for the island, much as the Java programming language shares its name with an Indonesian island . The island is mentioned in the 13th century treaty of Novgorod with Hanseatic League and Gotland , once as "Kotlign" and twice as "Kotling". The city of Kronstadt was founded on Kotlin island by Peter the Great , who took it from the Swedes in 1703. In March 1921, Kotlin

118-431: A JvmName annotation which specifies a class name used when the package is viewed from a Java project. For example, @file:JvmName("JavaClassName") . As in C , C++ , C# , Java, and Go , the entry point to a Kotlin program is a function named "main", which may be passed an array containing any command-line arguments. This is optional since Kotlin 1.3. Perl , PHP , and Unix shell –style string interpolation

177-406: A date could be stored as a record containing a numeric year field, a month field represented as a string, and a numeric day-of-month field. A circle record might contain a numeric radius and a center that is a point record containing x and y coordinates. Notable applications include the programming language record type and for row-based storage, data organized as

236-498: A derived class is disabled unless the base class is declared with the open keyword. In addition to the classes and member functions (which are equivalent to methods) of object-oriented programming, Kotlin also supports procedural programming with the use of functions . Kotlin functions and constructors support default arguments , variable-length argument lists, named arguments , and overloading by unique signature. Class member functions are virtual, i.e. dispatched based on

295-563: A gradual migration from Java to Kotlin. Borrowing from Scala , semicolons are optional as a statement terminator ; in most cases a newline is sufficient for the compiler to deduce that the statement has ended. Borrowing from Scala , Kotlin variable declarations and parameter lists have the data type come after the variable name (and with a colon separator), similar to Ada , BASIC , Pascal , TypeScript and Rust . This, according to an article from Roman Elizarov, current project lead, results in alignment of variable names and

354-443: A new class from a base class type, the base class needs to be explicitly marked as "open". This is in contrast to most object-oriented languages such as Java where classes are open by default. Example of a base class that is open to deriving a new subclass from it: Abstract classes define abstract or "pure virtual" placeholder functions that will be defined in a derived class. Abstract classes are open by default. Kotlin provides

413-422: A record can be traced to various types of tables and ledgers used in accounting since remote times. The modern notion of records in computer science, with fields of well-defined type and size, was already implicit in 19th century mechanical calculators, such as Babbage 's Analytical Engine . The original machine-readable medium used for data (as opposed to control) was the punch card used for records in

472-405: A record was the smallest unit that could be read from external storage (e.g., card reader, tape, or disk). The contents of punchcard-style records were originally called "unit records" because punchcards had pre-determined document lengths. When storage systems became more advanced with the use of hard drives and magnetic tape , variable-length records became the standard. A variable-length record

531-840: A sequence of records, such as a database table , spreadsheet or comma-separated values (CSV) file. In general, a record type value is stored in memory and row-based storage is in mass storage . A record type is a data type that describes such values and variables. Most modern programming languages allow the programmer to define new record types. The definition includes specifying the data type of each field and an identifier (name or label) by which it can be accessed. In type theory , product types (with no field names) are generally preferred due to their simplicity, but proper record types are studied in languages such as System F-sub . Since type-theoretical records may contain first-class function -typed fields in addition to data, they can express many features of object-oriented programming . In

590-491: Is a record in which the size of the record in bytes is approximately equal to the sum of the sizes of its fields. This was not possible to do before more advanced storage hardware was invented because all of the punchcards had to conform to pre-determined document lengths that the computer could read, since at the time the cards had to be physically fed into a machine. Most machine language implementations and early assembly languages did not have special syntax for records, but

649-485: Is associated with a record variable where data is read into or written from. COBOL also provides a MOVE CORRESPONDING statement that assigns corresponding fields of two records according to their names. The early languages developed for numeric computing, such as FORTRAN (up to FORTRAN IV ) and ALGOL 60 , did not support record types; but later versions of those languages, such as FORTRAN 77 and ALGOL 68 did add them. The original Lisp programming language too

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708-563: Is derived from Kotlin Island , a Russian island in the Gulf of Finland , near St. Petersburg . Andrey Breslav , Kotlin's former lead designer, mentioned that the team decided to name it after an island, just like the programming language Java was named after the Indonesian island of Java (though the language's name is said to have been inspired by the Java variety of coffee, which itself

767-452: Is derived from the island name). In July 2011, JetBrains unveiled Project Kotlin, a new language for the JVM, which had been under development for a year. JetBrains lead Dmitry Jemerov said that most languages did not have the features they were looking for, with the exception of Scala . However, he cited the slow compilation time of Scala as a deficiency. One of the stated goals of Kotlin

826-593: Is designed to interoperate fully with Java , and the JVM version of Kotlin's standard library depends on the Java Class Library , but type inference allows its syntax to be more concise. Kotlin mainly targets the JVM, but also compiles to JavaScript (e.g., for frontend web applications using React ) or native code via LLVM (e.g., for native iOS apps sharing business logic with Android apps). Language development costs are borne by JetBrains , while

885-561: Is more pleasing to eyes, especially when there are a few variable declarations in succession, and one or more of the types is too complex for type inference, or needs to be declared explicitly for human readers to understand. Borrowing from Scala , variables in Kotlin can be read-only, declared with the val keyword, or mutable , declared with the var keyword. Borrowing from Scala , class members are public by default, and classes themselves are final by default, meaning that creating

944-399: Is needed for a class, a more general constructor can be defined using secondary constructor syntax , which closely resembles the constructor syntax used in most object-oriented languages like C++, C#, and Java. Sealed classes and interfaces restrict subclass hierarchies, meaning more control over the inheritance hierarchy. Declaration of sealed interface and class: All the subclasses of

1003-401: Is supported. Type inference is also supported. Similar to C#, Kotlin allows adding an extension function to any class without the formalities of creating a derived class with new functions. An extension function has access to all the public interface of a class, which it can use to create a new function interface to a target class. An extension function will appear exactly like a function of

1062-681: Is to compile as quickly as Java. In February 2012, JetBrains open sourced the project under the Apache 2 license . JetBrains hoped that the new language would drive IntelliJ IDEA sales. The first commit to the Kotlin Git repository was on November 8, 2010. Kotlin 1.0 was released on February 15, 2016. This is considered to be the first officially stable release and JetBrains has committed to long-term backwards compatibility starting with this version. At Google I/O 2017, Google announced first-class support for Kotlin on Android . Kotlin 1.2

1121-399: The 1890 United States Census : each punch card was a single record. Compare the journal entry from 1880 and the punch card from 1895. Records were well-established in the first half of the 20th century, when most data processing was done using punched cards. Typically, each record of a data file would be recorded on one punched card, with specific columns assigned to specific fields. Generally,

1180-546: The Kotlin Foundation protects the Kotlin trademark. On 7 May 2019, Google announced that the Kotlin programming language was now its preferred language for Android app developers. Since the release of Android Studio 3.0 in October 2017, Kotlin has been included as an alternative to the standard Java compiler. The Android Kotlin compiler produces Java 8 bytecode by default (which runs in any later JVM), but lets

1239-670: The Kotlin programming language is now its preferred language for Android app developers. Kotlin 1.4 was released in August 2020, with e.g. some slight changes to the support for Apple's platforms, i.e. to the Objective-C / Swift interop . Kotlin 1.5 was released in May 2021. Kotlin 1.6 was released in November 2021. Kotlin 1.7 was released in June 2022, including the alpha version of

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1298-545: The class and will be shown in code completion inspection of class functions. For example: By placing the preceding code in the top-level of a package, the String class is extended to include a lastChar function that was not included in the original definition of the String class. Kotlin has five scope functions, which allow the changing of scope within the context of an object . The scope functions are let , run , with , apply , and also . Similar to Python,

1357-431: The class name. This argument list supports an expanded syntax on Kotlin's standard function argument lists that enables declaration of class properties in the primary constructor, including visibility, extensibility, and mutability attributes. Additionally, when defining a subclass, properties in super-interfaces and super-classes can be overridden in the primary constructor. However, in cases where more than one constructor

1416-451: The comparison of two record values for equality. Some languages may also allow order comparisons ('<'and '>'), using the lexicographic order based on the comparison of individual fields. PL/I allows both of the preceding types of assignment, and also allows structure expressions , such as a = a+1; where "a" is a record, or structure in PL/I terminology. In Algol 68, if Pts

1475-401: The concept of records. These languages allow the programmer to store sets of data, which are essentially records, in tables. This data can then be retrieved using a primary key . The tables themselves are also records which may have a foreign key : a key that references data in another table.    Operations for a record type include: Some languages provide facilities that enumerate

1534-501: The concept was available (and extensively used) through the use of index registers , indirect addressing , and self-modifying code . Some early computers, such as the IBM 1620 , had hardware support for delimiting records and fields, and special instructions for copying such records. The concept of records and fields was central in some early file sorting and tabulating utilities, such as IBM's Report Program Generator (RPG) . COBOL

1593-421: The context of storage such as in a database or spreadsheet a record is often called a row and each field is called a column . In object-oriented programming , an object is a record that contains state and method fields. A record is similar to a mathematical tuple , although a tuple may or may not be considered a record, and vice versa, depending on conventions and the programming language. In

1652-436: The corresponding field variable by their positions within the record; so that, for example, a complex number with fields called real and imag can be assigned to a 2D point record variable with fields X and Y . In this alternative, the two operands are still required to have the same sequence of field types. Some languages may also require that corresponding types have the same size and encoding as well, so that

1711-482: The fields of a record. This facility is needed to implement certain services such as debugging , garbage collection , and serialization . It requires some degree of type polymorphism . In contexts that support record subtyping, operations include adding and removing fields of a record. A specific record type implies that a specific set of fields are present, but values of that type may contain additional fields. A record with fields x , y , and z would thus belong to

1770-433: The fields of record R had been declared as variables. Similarly to entering a different namespace in an object-oriented language like C# , it is no longer necessary to use the record name as a prefix to access the fields. So, instead of writing Pt.X := 5; Pt.Y := Pt.X + 3 one could write with Pt do begin X := 5 ; Y := X + 3 end . The representation of a record in memory varies depending on

1829-402: The following keywords to restrict visibility for top-level declaration, such as classes, and for class members: public , internal , protected , and private . When applied to a class member: When applied to a top-level declaration: Example: Kotlin supports the specification of a "primary constructor" as part of the class definition itself, consisting of an argument list following

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1888-465: The key methods equals , hashCode and toString are automatically generated from the class properties. Unlike Java's records, data classes are open for inheritance. Record (computer science) In computer science , a record (also called a structure , struct , or compound data type ) is a composite data structure – a collection of fields , possibly of different data types , typically fixed in number and sequence. For example,

1947-483: The low overhead and ability to use records in assembly language make records still relevant when programming with low levels of abstraction . Today, the most popular languages on the TIOBE index , an indicator of the popularity of programming languages, have been influenced in some way by records due to the fact that they are object oriented. Query languages such as SQL and Object Query Language were also influenced by

2006-445: The machine—say, that a floating point field must occupy a single word. Some languages may implement a record as an array of addresses pointing to the fields (and, possibly, to their names and/or types). Objects in object-oriented languages are often implemented in rather complicated ways, especially in languages that allow multiple class inheritance . A self-defining record is a type of record which contains information to identify

2065-511: The matter is a central characteristic of record types in more theoretical contexts. Most languages allow assignment between records that have exactly the same record type (including same field types and names, in the same order). Depending on the language, however, two record data types defined separately may be regarded as distinct types even if they have exactly the same fields. Some languages may also allow assignment between records whose fields have different names, matching each field value with

2124-662: The new Kotlin K2 compiler . Kotlin 1.8 was released in December 2022, 1.8.0 was released on January 11, 2023. Kotlin 1.9 was released in July 2023, 1.9.0 was released on July 6, 2023. Kotlin 2.0 was released in May 2024, 2.0.0 was released on May 21, 2024. Development lead Andrey Breslav has said that Kotlin is designed to be an industrial-strength object-oriented language, and a "better language" than Java , but still be fully interoperable with Java code, allowing companies to make

2183-438: The organization and will be the primary key. Depending on the storage medium and file organization, the employee number might be indexed —that is also stored in a separate file to make the lookup faster. The department code is not necessarily unique; it may also be indexed, in which case it would be considered a secondary key , or alternate key . If it is not indexed, the entire employee file would have to be scanned to produce

2242-585: The programmer choose to target Java 9 up to 20, for optimization, or allows for more features; has bidirectional record class interoperability support for JVM, introduced in Java 16, considered stable as of Kotlin 1.5. Kotlin has support for the web with Kotlin/JS, through an intermediate representation -based backend which has been declared stable since version 1.8, released December 2022. Kotlin/Native (for e.g. Apple silicon support) has been declared stable since version 1.9.20, released November 2023. The name

2301-464: The programming language. Often, fields are stored in consecutive memory locations, in the same order as they are declared in the record type. This may result in two or more fields stored into the same word of memory; indeed, this feature is often used in systems programming to access specific bits of a word. On the other hand, most compilers will add padding fields, mostly invisible to the programmer, in order to comply with alignment constraints imposed by

2360-460: The purpose of containing data), records influenced newer object-oriented programming languages and relational database management systems. Since records provided more modularity in the way data was stored and handled, they are better suited at representing complex, real-world concepts than the primitive data types provided by default in languages. This influenced later languages such as C++ , Python , JavaScript , and Objective-C which address

2419-474: The record type and to locate information within the record. It may contain the offsets of elements; the elements can therefore be stored in any order or may be omitted. The information stored in a self-defining record can be interpreted as metadata for the record, which is similar to what one would expect to find in the UNIX metadata regarding a file, containing information such as the record's creation time and

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2478-622: The rock on which the Tolbaaken lighthouse is built. The island thus divides the seaward approach to St Petersburg into two channels; that on the northern side is obstructed by shoals which extend across it from Kotlin to Lisiy Nos ; the southern channel, the highway to the former capital, is narrowed by a spit which projects from opposite Lomonosov on the Russian mainland, and, lying close to Kronstadt, has been historically strongly guarded by batteries . The naval approach to Saint Petersburg

2537-410: The runtime type of the object they are called on. Kotlin 1.3 added support for contracts, which are stable for the standard library declarations, but still experimental for user-defined declarations. Contracts are inspired by Eiffel's design by contract programming paradigm. Following ScalaJS , Kotlin code may be transpiled to JavaScript , allowing for interoperability between code written in

2596-433: The same modularity needs of programming. Objects in these languages are essentially records with the addition of methods and inheritance , which allow programmers to manipulate the way data behaves instead of only the contents of a record. Many programmers regard records as obsolete now since object-oriented languages have features that far surpass what records are capable of. On the other hand, many programmers argue that

2655-410: The same type. The parameters of a function can be viewed collectively as the fields of a record and passing arguments to the function can be viewed as assigning the input parameters to the record fields. At a low-level, a function call includes an activation record or call frame , that contains the parameters as well as other fields such as local variables and the return address. The concept of

2714-464: The same vein, a record type can be viewed as the computer language analog of the Cartesian product of two or more mathematical sets , or the implementation of an abstract product type in a specific language. A record differs from an array in that a record's elements (fields) are determined by the definition of the record, and may be heterogeneous whereas an array is a collection of elements with

2773-426: The sealed class are defined at compile time. No new subclasses can be added to it after the compilation of the module having the sealed class. For example, a sealed class in a compiled jar file cannot be subclassed. Kotlin's data class construct defines classes whose primary purpose is storing data, similar Java's record types. Like Java's record types, the construct is similar to normal classes except that

2832-571: The size of the record in bytes . Alternatively, various elements of the record, each including an element identifier, can simply follow one another in any order. A record, especially in the context of row-based storage, may include key fields that allow indexing the records of a collection. A primary key is unique throughout all stored records; only one of this key exists. In other words, no duplicate may exist for any primary key. For example, an employee file might contain employee number, name, department, and salary. The employee number will be unique in

2891-541: The spread operator asterisk (*) unpacks an array's contents as individual arguments to a function, e.g: Destructuring declarations decompose an object into multiple variables at once, e.g. a 2D coordinate object might be destructured into two integers, x and y . For example, the Map.Entry object supports destructuring to simplify access to its key and value fields: Kotlin allows local functions to be declared inside of other functions or methods. In Kotlin, to derive

2950-430: The two languages. This can be used either to write full web applications in Kotlin, or to share code between a Kotlin backend and a JavaScript frontend. Kotlin relaxes Java's restriction of allowing static methods and variables to exist only within a class body. Static objects and functions can be defined at the top level of the package without needing a redundant class level. For compatability with Java, Kotlin provides

3009-421: The type of records with fields x and y , as would a record with fields x , y , and r . The rationale is that passing an ( x , y , z ) record to a function that expects an ( x , y ) record as argument should work, since that function will find all the fields it requires within the record. Many ways of practically implementing records in programming languages would have trouble with allowing such variability, but

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3068-463: The whole record can be assigned as an uninterpreted bit string . Other languages may be more flexible in this regard, and require only that each value field can be legally assigned to the corresponding variable field; so that, for example, a short integer field can be assigned to a long integer field, or vice versa. Other languages (such as COBOL ) may match fields and values by their names, rather than positions. These same possibilities apply to

3127-405: Was an array of records, each with integer fields X and Y , one could write Y of Pts to obtain an array of integers, consisting of the Y fields of all the elements of Pts . As a result, the statements Y of Pts[3] := 7 and (Y of Pts)[3] := 7 would have the same effect. In Pascal , the command with R do S would execute the command sequence S as if all

3186-419: Was an incentive to build a Sea Canal to accommodate large vessels, this canal allows the movement of vessels with a draft of 11 metres (to fresh water), a length of 320 metres and a width of 42 metres. Kotlin (programming language) Kotlin ( / ˈ k ɒ t l ɪ n / ) is a cross-platform , statically typed , general-purpose high-level programming language with type inference . Kotlin

3245-560: Was greatly facilitated by the construction in 1875–85 of a canal , 7 m (23 ft) deep, through the shallows, whereas cars can travel overland to the island by using the Saint Petersburg Dam from the north and south shores of the Gulf of Finland . Started in 1980, but delayed by political upheaval in the 1990s, the dam project was completed in 2010 and officially commissioned in 2011. The low water depth in Neva Bay

3304-595: Was lacking records (except for the built-in cons cell ), but its S-expressions provided an adequate surrogate. The Pascal programming language was one of the first languages to fully integrate record types with other basic types into a logically consistent type system. The PL/I language provided for COBOL-style records. The C language provides the record concept using struct s. Most languages designed after Pascal (such as Ada , Modula , and Java ), also supported records. Although records are not often used in their original context anymore (i.e. being used solely for

3363-442: Was released on November 28, 2017. Sharing code between JVM and JavaScript platforms feature was newly added to this release (multiplatform programming is by now a beta feature upgraded from "experimental"). A full-stack demo has been made with the new Kotlin/JS Gradle Plugin. Kotlin 1.3 was released on 29 October 2018, adding support for coroutines for use with asynchronous programming. On 7 May 2019, Google announced that

3422-443: Was the first widespread programming language to support record types, and its record definition facilities were quite sophisticated at the time. The language allows for the definition of nested records with alphanumeric, integer, and fractional fields of arbitrary size and precision, and fields that automatically format any value assigned to them (e.g., insertion of currency signs, decimal points, and digit group separators). Each file

3481-466: Was the site of the Kronstadt rebellion , which resulted in over 11,000 casualties. In general outline, the island forms an elongated triangle; 12.1 km (7.5 mi) long by about 1.6 km (1.0 mi) broad, with its base towards St Petersburg. The eastern or broad end is occupied by the city of Kronstadt, and shoals extend for 2.4 km (1.5 mi) from the western point of the island to

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