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Nullable types are a feature of some programming languages which allow the value to be set to the special value NULL instead of the usual possible values of the data type. In statically-typed languages, a nullable type is an option type, while in dynamically-typed languages (where values have types, but variables do not), equivalent behavior is provided by having a single null value.
In computer science and computer programming, a data type or simply type is an attribute of data which tells the compiler or interpreter how the programmer intends to use the data. Most programming languages support common data types of real, integer and boolean. A data type constrains the values that an expression, such as a variable or a function, might take. This data type defines the operations that can be done on the data, the meaning of the data, and the way values of that type can be stored. A type of value from which an expression may take its value.
In programming languages and type theory, an option type or maybe type is a polymorphic type that represents encapsulation of an optional value; e.g., it is used as the return type of functions which may or may not return a meaningful value when they are applied. It consists of a constructor which either is empty, or which encapsulates the original data type
NULL is frequently used to represent a missing value or invalid value, such as from a function that failed to return or a missing field in a database, as in NULL in SQL.
Null is a special marker used in Structured Query Language to indicate that a data value does not exist in the database. Introduced by the creator of the relational database model, E. F. Codd, SQL Null serves to fulfil the requirement that all true relational database management systems (RDBMS) support a representation of "missing information and inapplicable information". Codd also introduced the use of the lowercase Greek omega (ω) symbol to represent Null in database theory. In SQL,
NULL is a reserved word used to identify this marker.
SQL is a domain-specific language used in programming and designed for managing data held in a relational database management system (RDBMS), or for stream processing in a relational data stream management system (RDSMS). It is particularly useful in handling structured data where there are relations between different entities/variables of the data. SQL offers two main advantages over older read/write APIs like ISAM or VSAM. First, it introduced the concept of accessing many records with one single command; and second, it eliminates the need to specify how to reach a record, e.g. with or without an index.
Primitive types such as integers and Booleans cannot generally be null, but the corresponding nullable types (nullable integer and nullable Boolean, respectively) can also assume the NULL value.[ jargon ]
An integer is a number that can be written without a fractional component. For example, 21, 4, 0, and −2048 are integers, while 9.75, 5 1/2, and √2 are not.
An integer variable may represent integers, but 0 (zero) is a special case because 0 in many programming languages can mean "false". Also this doesn't give us any notion of saying that the variable is empty, a need for which occurs in many circumstances. This need can be achieved with a nullable type. In programming languages like C# 2.0, a nullable integer, for example, can be declared by a question mark (int? x).In programming languages like C# 1.0, nullable types can be defined by an external library as new types (e.g. NullableInteger, NullableBoolean).
C# is a general-purpose, multi-paradigm programming language encompassing strong typing, lexically scoped, imperative, declarative, functional, generic, object-oriented (class-based), and component-oriented programming disciplines. It was developed around 2000 by Microsoft as part of its .NET initiative, and later approved as an international standard by Ecma (ECMA-334) and ISO. Mono is the name of the free and open-source project to develop a compiler and runtime for the language. C# is one of the programming languages designed for the Common Language Infrastructure (CLI).
A Boolean variable makes the effect more clear. Its values can be either "true" or "false", while a nullable boolean may also contain a representation for "undecided". However, the interpretation or treatment of a logical operation involving such a variable depends on the language.
In contrast, object pointers can be set to NULL by default in most common languages, meaning that the pointer or reference points to nowhere, that no object is assigned (the variable does not point to any object). Nullable references were invented by C. A. R. Hoare in 1965 as part of the Algol W language. Hoare later described his invention as a "billion-dollar mistake".This is because object pointers that can be NULL require the user to check the pointer before using it and require specific code to handle the case when the object pointer is NULL.
In computer science, a pointer is a programming language object that stores the memory address of another value located in computer memory. A pointer references a location in memory, and obtaining the value stored at that location is known as dereferencing the pointer. As an analogy, a page number in a book's index could be considered a pointer to the corresponding page; dereferencing such a pointer would be done by flipping to the page with the given page number and reading the text found on that page. The actual format and content of a pointer variable is dependent on the underlying computer architecture.
In computing, a null pointer or null reference has a value reserved for indicating that the pointer or reference does not refer to a valid object. Programs routinely use null pointers to represent conditions such as the end of a list of unknown length or the failure to perform some action; this use of null pointers can be compared to nullable types and to the Nothing value in an option type.
Java has classes that correspond to scalar values, such as Integer, Boolean and Float. Combined with autoboxing (automatic usage-driven conversion between object and value), this effectively allows nullable variables for scalar values.[ citation needed ]
Java is a general-purpose programming language that is class-based, object-oriented, and designed to have as few implementation dependencies as possible. It is intended to let application developers write once, run anywhere (WORA), meaning that compiled Java code can run on all platforms that support Java without the need for recompilation. Java applications are typically compiled to bytecode that can run on any Java virtual machine (JVM) regardless of the underlying computer architecture. The syntax of Java is similar to C and C++, but it has fewer low-level facilities than either of them. As of 2019, Java was one of the most popular programming languages in use according to GitHub, particularly for client-server web applications, with a reported 9 million developers.
Nullable type implementations usually adhere to the null object pattern.
There is a more general and formal concept that extend the nullable type concept, it comes from option types, which enforce explicit handling of the exceptional case. Option type implementations usually adhere to the Special Case pattern.
The following programming languages support nullable types.
Statically typed languages with native null support include:
Statically typed languages with library null support include:
Dynamically-typed languages with null include:
In computer programming, a parameter or a formal argument, is a special kind of variable, used in a subroutine to refer to one of the pieces of data provided as input to the subroutine. These pieces of data are the values of the arguments with which the subroutine is going to be called/invoked. An ordered list of parameters is usually included in the definition of a subroutine, so that, each time the subroutine is called, its arguments for that call are evaluated, and the resulting values can be assigned to the corresponding parameters.
In computer science, primitive data type is either of the following:
In computer science, type conversion, type casting, type coercion, and type juggling are different ways of changing an expression from one data type to another. An example would be the conversion of an integer value into a floating point value or its textual representation as a string, and vice versa. Type conversions can take advantage of certain features of type hierarchies or data representations. Two important aspects of a type conversion are whether it happens implicitly (automatically) or explicitly, and whether the underlying data representation is converted from one representation into another, or a given representation is merely reinterpreted as the representation of another data type. In general, both primitive and compound data types can be converted.
In computer programming,
?: is a ternary operator that is part of the syntax for basic conditional expressions in several programming languages. It is commonly referred to as the conditional operator, inline if (iif), or ternary if. An expression
a? b : c evaluates to
b if the value of
a is true, and otherwise to
This article compares two programming languages: C# with Java. While the focus of this article is mainly the languages and their features, such a comparison will necessarily also consider some features of platforms and libraries. For a more detailed comparison of the platforms, please see Comparison of the Java and .NET platforms.
In computer science, the Boolean data type is a data type that has one of two possible values, intended to represent the two truth values of logic and Boolean algebra. It is named after George Boole, who first defined an algebraic system of logic in the mid 19th century. The Boolean data type is primarily associated with conditional statements, which allow different actions by changing control flow depending on whether a programmer-specified Boolean condition evaluates to true or false. It is a special case of a more general logical data type —logic doesn't always need to be Boolean.
In computer programming, a sigil is a symbol affixed to a variable name, showing the variable's datatype or scope, usually a prefix, as in
$ is the sigil.
In computer programming, a semipredicate problem occurs when a subroutine intended to return a useful value can fail, but the signalling of failure uses an otherwise valid return value. The problem is that the caller of the subroutine cannot tell what the result means in this case.
Generics are a facility of generic programming that were added to the Java programming language in 2004 within version J2SE 5.0. They were designed to extend Java's type system to allow "a type or method to operate on objects of various types while providing compile-time type safety". The aspect compile-time type safety was not fully achieved, since it was shown in 2016 that it is not guaranteed in all cases.
The null coalescing operator is a binary operator that is part of the syntax for a basic conditional expression in several programming languages, including C#, Perl as of version 5.10, Swift, and PHP 7.0.0. While its behavior differs between implementations, the null coalescing operator generally returns the result of its left-most operand if it exists and is not null, and otherwise returns the right-most operand. This behavior allows a default value to be defined for cases where a more specific value is not available.
In computer programming, a variable or scalar is a storage location paired with an associated symbolic name, which contains some known or unknown quantity of information referred to as a value. The variable name is the usual way to reference the stored value, in addition to referring to the variable itself, depending on the context. This separation of name and content allows the name to be used independently of the exact information it represents. The identifier in computer source code can be bound to a value during run time, and the value of the variable may thus change during the course of program execution.
Void safety is a guarantee within an object-oriented programming language that no object references will have null or void values.
In computing, undefined value is a condition where an expression does not have a correct value, although it is syntactically correct. An undefined value must not be confused with empty string, boolean "false" or other "empty" values. Depending on circumstances, evaluation to an undefined value may lead to exception or undefined behaviour, but in some programming languages undefined values can occur during a normal, predictable course of program execution.
In computer programming, programming languages are often colloquially classified as to whether the language's type system makes it strongly typed or weakly typed. Generally, a strongly typed language has stricter typing rules at compile time, which implies that errors and exceptions are more likely to happen during compilation. However, dynamically typed languages can also be strongly typed. Most of these rules affect variable assignment, return values and function calling. On the other hand, a weakly typed language has looser typing rules and may produce unpredictable results or may perform implicit type conversion at runtime. A different but related concept is latent typing.
In certain computer programming languages, the Elvis operator, often written
||, is a binary operator that returns its first operand if that operand evaluates to a true value, and otherwise evaluates and returns its second operand. The Elvis operator is a variant of the ternary conditional operator,
? : in the sense that the expression with the Elvis operator
A ?: B is approximately equivalent to the expression with the ternary operator
A? A : B.
Swift is a general-purpose, multi-paradigm, compiled programming language developed by Apple Inc. for iOS, macOS, watchOS, tvOS, Linux, and z/OS. Swift is designed to work with Apple's Cocoa and Cocoa Touch frameworks and the large body of existing Objective-C code written for Apple products. It is built with the open source LLVM compiler framework and has been included in Xcode since version 6, released in 2014. On Apple platforms, it uses the Objective-C runtime library which allows C, Objective-C, C++ and Swift code to run within one program.