List of JAVA keywords
;_
:Added in Java 9, the underscore has become a keyword and cannot be used as a variable name anymore.
; abstract
: A method with no definition must be declared as abstract and the class containing it must be declared as abstract. Abstract classes cannot be instantiated. Abstract methods must be implemented in the sub classes. The abstract keyword cannot be used with variables or constructors. Note that an abstract class isn't required to have an abstract method at all.
;assert
Assertion or assert may refer to:
Computing
* Assertion (software development), a computer programming technique
* assert.h, a header file in the standard library of the C programming language
* Assertion definition language, a specification lang ...
(added in J2SE 1.4)
:Assert describes a predicate (a true–false statement) placed in a Java program to indicate that the developer thinks that the predicate is always true at that place. If an assertion evaluates to false at run-time, an assertion failure results, which typically causes execution to abort. Assertions are disabled at runtime by default, but can be enabled through a command-line option or programmatically through a method on the class loader.
:
;boolean
Any kind of logic, function, expression, or theory based on the work of George Boole is considered Boolean.
Related to this, "Boolean" may refer to:
* Boolean data type, a form of data with only two possible values (usually "true" and "false" ...
:Defines a boolean variable for the values "true" or "false" only. By default, the value of boolean primitive type is false. This keyword is also used to declare that a method returns a value of the primitive type boolean
Any kind of logic, function, expression, or theory based on the work of George Boole is considered Boolean.
Related to this, "Boolean" may refer to:
* Boolean data type, a form of data with only two possible values (usually "true" and "false" ...
.
;break
Break or Breaks or The Break may refer to:
Time off from duties
* Recess (break), time in which a group of people is temporarily dismissed from its duties
* Break (work), time off during a shift/recess
** Coffee break, a short mid-morning rest ...
:Used to end the execution in the current loop body.
:Used to break out of a switch
In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type of ...
block.
;byte
The byte is a unit of digital information that most commonly consists of eight bits. Historically, the byte was the number of bits used to encode a single character of text in a computer and for this reason it is the smallest addressable unit ...
:The byte
keyword is used to declare a field that can hold an 8-bit signed two's complement integer. This keyword is also used to declare that a method returns a value of the primitive type byte
.
;case
Case or CASE may refer to:
Containers
* Case (goods), a package of related merchandise
* Cartridge case or casing, a firearm cartridge component
* Bookcase, a piece of furniture used to store books
* Briefcase or attaché case, a narrow box to c ...
:A statement in the switch
In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type of ...
block can be labeled with one or more case
Case or CASE may refer to:
Containers
* Case (goods), a package of related merchandise
* Cartridge case or casing, a firearm cartridge component
* Bookcase, a piece of furniture used to store books
* Briefcase or attaché case, a narrow box to c ...
or default
labels. The switch
In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type of ...
statement evaluates its expression, then executes all statements that follow the matching case
Case or CASE may refer to:
Containers
* Case (goods), a package of related merchandise
* Cartridge case or casing, a firearm cartridge component
* Bookcase, a piece of furniture used to store books
* Briefcase or attaché case, a narrow box to c ...
label; see switch
In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type of ...
.
;catch
Catch may refer to:
In sports
* Catch (game), children's game
* Catch (baseball), a maneuver in baseball
* Catch (cricket), a mode of dismissal in cricket
* Catch or reception (gridiron football)
* Catch, part of a rowing stroke
In music
* Catc ...
:Used in conjunction with a try
block and an optional finally
block. The statements in the catch
block specify what to do if a specific type of exception is thrown by the try
block.
;char
Char may refer to:
People
*Char Fontane, American actress
*Char Margolis, American spiritualist
* René Char (1907–1988), French poet
*The Char family of Colombia:
** Fuad Char, Colombian senator
** Alejandro Char Chaljub, mayor of Barranquilla ...
:Defines a character variable capable of holding any character of the java source file's character set.
;class
Class or The Class may refer to:
Common uses not otherwise categorized
* Class (biology), a taxonomic rank
* Class (knowledge representation), a collection of individuals or objects
* Class (philosophy), an analytical concept used differentl ...
:A type that defines the implementation of a particular kind of object. A class definition defines const
In some programming languages, const is a type qualifier (a keyword applied to a data type) that indicates that the data is read-only. While this can be used to declare constants, in the C family of languages differs from similar constructs in ...
:Unused but reserved.
; continue
:Used to resume program execution at the end of the current loop body. If followed by a label, continue
resumes execution at the end of the enclosing labeled loop body.
;default
:The default
keyword can optionally be used in a case
matches the specified value; see ''switch
In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type of ...
''. Alternatively, the default
keyword can also be used to declare default values in a default
keyword can be used to allow an interface to provide an implementation of a method.
; do
:The do
keyword is used in conjunction with while
to create a do-while loop, which executes a block of statements associated with the loop and then tests a boolean expression associated with the while
. If the expression evaluates to true
, the block is executed again; this continues until the expression evaluates to false
.
;double
A double is a look-alike or doppelgänger; one person or being that resembles another.
Double, The Double or Dubble may also refer to:
Film and television
* Double (filmmaking), someone who substitutes for the credited actor of a character
* Th ...
:The double
keyword is used to declare a variable that can hold a 64-bit double
.
; else
:The else
keyword is used in conjunction with if
to create an if-else statement, which tests a true
, the block of statements associated with the if
are evaluated; if it evaluates to false
, the block of statements associated with the else
are evaluated.
;enum
Telephone number mapping is a system of unifying the international telephone number system of the public switched telephone network with the Internet addressing and identification name spaces. Internationally, telephone numbers are systematically ...
(added in extends
:Used in a class declaration to specify the superclass; used in an interface declaration to specify one or more superinterfaces. Class X extends class Y to add functionality, either by adding fields or methods to class Y, or by overriding methods of class Y. An interface Z extends one or more interfaces by adding methods. Class X is said to be a subclass of class Y; Interface Z is said to be a subinterface of the interfaces it extends.
:Also used to specify an upper bound on a type parameter in Generics.
;final
Final, Finals or The Final may refer to:
*Final (competition), the last or championship round of a sporting competition, match, game, or other contest which decides a winner for an event
** Another term for playoffs, describing a sequence of cont ...
:Define an entity once that cannot be changed nor derived from later. More specifically: a final class cannot be subclassed, a final method cannot be overridden, and a final variable can occur at most once as a left-hand expression on an executed command. All methods in a final class are implicitly final
.
;finally
Finally may refer to:
Albums
* ''Finally'' (Namie Amuro album) (2017)
* ''Finally'' (Blackstreet album) or its title song
* ''Finally'' (Sean Ensign album) or its title song "It's My Life (Finally)"
* ''Finally'' (Layzie Bone & A.K. album) ...
:Used to define a block of statements for a block defined previously by the try
keyword. The finally
block is executed after execution exits the try
block and any associated catch
clauses regardless of whether an exception was thrown or caught, or execution left method in the middle of the try
or catch
blocks using the return
keyword.
;float
Float may refer to:
Arts and entertainment Music Albums
* ''Float'' (Aesop Rock album), 2000
* ''Float'' (Flogging Molly album), 2008
* ''Float'' (Styles P album), 2013
Songs
* "Float" (Tim and the Glory Boys song), 2022
* "Float", by Bush ...
:The float
keyword is used to declare a variable that can hold a 32-bit float
.
;for
For or FOR may refer to:
English language
*For, a preposition
*For, a complementizer
*For, a grammatical conjunction
Science and technology
* Fornax, a constellation
* for loop, a programming language statement
* Frame of reference, in physic ...
:The for
keyword is used to create a true
, the block of statements associated with the loop are executed, and then the incrementation is performed. The boolean expression is then evaluated again; this continues until the expression evaluates to false
.
:As of for
keyword can also be used to create a so-called " enhanced for loop", which specifies an Iterable
.
;goto
GoTo (goto, GOTO, GO TO or other case combinations, depending on the programming language) is a statement found in many computer programming languages. It performs a one-way transfer of control to another line of code; in contrast a function ca ...
:Unused but reserved.
; if
:The if
keyword is used to create an true
, the block of statements associated with the if statement is executed. This keyword can also be used to create an if-else statement; see '' else
''.
;implements
:Included in a class declaration to specify one or more import
:Used at the beginning of a import
statements can import static
members of a class.
;instanceof
:A instanceof
operator evaluates to true if and only if the runtime type of the object is assignment compatible with the class or interface.
; int
:The int
keyword is used to declare a variable that can hold a 32-bit signed two's complement integer. This keyword is also used to declare that a method returns a value of the primitive type int
.
;interface
Interface or interfacing may refer to:
Academic journals
* ''Interface'' (journal), by the Electrochemical Society
* ''Interface, Journal of Applied Linguistics'', now merged with ''ITL International Journal of Applied Linguistics''
* '' Inte ...
:Used to declare a special type of class that only contains abstract or default methods, constant (static final
) fields and static
interfaces. It can later be implemented by classes that declare the interface with the implements
keyword. As long
Long may refer to:
Measurement
* Long, characteristic of something of great duration
* Long, characteristic of something of great length
* Longitude (abbreviation: long.), a geographic coordinate
* Longa (music), note value in early music mensur ...
:The long
keyword is used to declare a variable that can hold a 64-bit signed two's complement integer. This keyword is also used to declare that a method returns a value of the primitive type long
.
;native
Native may refer to:
People
* Jus soli, citizenship by right of birth
* Indigenous peoples, peoples with a set of specific rights based on their historical ties to a particular territory
** Native Americans (disambiguation)
In arts and entert ...
:Used in method declarations to specify that the method is not implemented in the same Java source file, but rather in another language.
;new
New is an adjective referring to something recently made, discovered, or created.
New or NEW may refer to:
Music
* New, singer of K-pop group The Boyz
Albums and EPs
* ''New'' (album), by Paul McCartney, 2013
* ''New'' (EP), by Regurgitator, ...
:Used to create an instance of a class or array object. Using keyword for this end is not completely necessary (as exemplified by Scala), though it serves two purposes: it enables the existence of different namespace for methods and class names, it defines statically and locally that a fresh object is indeed created, and of what runtime type it is (arguably introducing dependency into the code).
; package
:Java package is a group of similar classes and interfaces. Packages are declared with the package
keyword.
;private
Private or privates may refer to:
Music
* " In Private", by Dusty Springfield from the 1990 album ''Reputation''
* Private (band), a Denmark-based band
* "Private" (Ryōko Hirosue song), from the 1999 album ''Private'', written and also recorde ...
:The private
keyword is used in the declaration of a method, field, or inner class; private members can only be accessed by other members of their own class.
;protected
Protection is any measure taken to guard a thing against damage caused by outside forces. Protection can be provided to physical objects, including organisms, to systems, and to intangible things like civil and political rights. Although th ...
:The protected
keyword is used in the declaration of a method, field, or inner class; protected members can only be accessed by members of their own class, that class's subclasses or classes from the same package.
;public
In public relations and communication science, publics are groups of individual people, and the public (a.k.a. the general public) is the totality of such groupings. This is a different concept to the sociological concept of the ''Öffentlichkei ...
:The public
keyword is used in the declaration of a class, method, or field; public classes, methods, and fields can be accessed by the members of any class.
;return
Return may refer to:
In business, economics, and finance
* Return on investment (ROI), the financial gain after an expense.
* Rate of return, the financial term for the profit or loss derived from an investment
* Tax return, a blank document or t ...
:Used to finish the execution of a method. It can be followed by a value required by the method definition that is returned to the caller
;short
Short may refer to:
Places
* Short (crater), a lunar impact crater on the near side of the Moon
* Short, Mississippi, an unincorporated community
* Short, Oklahoma, a census-designated place
People
* Short (surname)
* List of people known as ...
:The short
keyword is used to declare a field that can hold a 16-bit signed two's complement integer. This keyword is also used to declare that a method returns a value of the primitive type short
.
;static
Static may refer to:
Places
*Static Nunatak, a nunatak in Antarctica
United States
* Static, Kentucky and Tennessee
*Static Peak, a mountain in Wyoming
**Static Peak Divide, a mountain pass near the peak
Science and technology Physics
*Static el ...
:Used to declare a field, method, or inner class as a class field. Classes maintain one copy of class fields regardless of how many instances exist of that class. static
also is used to define a method as a class method. Class methods are static
members of another class or interface are actually top-level classes and are ''not'' inner classes.
;super
Super may refer to:
Computing
* SUPER (computer program), or Simplified Universal Player Encoder & Renderer, a video converter / player
* Super (computer science), a keyword in object-oriented programming languages
* Super key (keyboard butt ...
:Inheritance basically used to achieve dynamic binding or run-time polymorphism in java. Used to access members of a class inherited by the class in which it appears. Allows a subclass to access overridden methods and hidden members of its superclass. The super
keyword is also used to forward a call from a constructor to a constructor in the superclass.
:Also used to specify a lower bound on a type parameter in Generics.
;switch
In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type of ...
:The switch
keyword is used in conjunction with case
Case or CASE may refer to:
Containers
* Case (goods), a package of related merchandise
* Cartridge case or casing, a firearm cartridge component
* Bookcase, a piece of furniture used to store books
* Briefcase or attaché case, a narrow box to c ...
and default
to create a case
, and executes the block of statements associated with that case
. If no case
matches the value, the optional block labelled by default
is executed, if included.
; synchronized
:Used in the declaration of a method or code block to acquire the Class
. Guarantees that at most one thread at a time operating on the same object executes that code. The mutex lock is automatically released when execution exits the synchronized code. Fields, classes and interfaces cannot be declared as ''synchronized''.
;this
This may refer to:
* ''This'', the singular proximal demonstrative pronoun
Places
* This, or ''Thinis'', an ancient city in Upper Egypt
* This, Ardennes, a commune in France
People with the surname
* Hervé This, French culinary chemist Arts, e ...
:Used to represent an instance of the class in which it appears. this
can be used to access class members and as a reference to the current instance. The this
keyword is also used to forward a call from one constructor in a class to another constructor in the same class.
;throw
Throwing is an action which consists in accelerating a projectile and then releasing it so that it follows a ballistic trajectory, usually with the aim of impacting a remote target. This action is best characterized for animals with prehensile l ...
:Causes the declared exception instance to be thrown. This causes execution to continue with the first enclosing exception handler declared by the catch
keyword to handle an assignment compatible exception type. If no such exception handler is found in the current method, then the method returns and the process is repeated in the calling method. If no exception handler is found in any method call on the stack, then the exception is passed to the thread's uncaught exception handler.
;throws
Throwing is an action which consists in accelerating a projectile and then releasing it so that it follows a ballistic trajectory, usually with the aim of impacting a remote target. This action is best characterized for animals with prehensile l ...
:Used in method declarations to specify which exceptions are not handled within the method but rather passed to the next higher level of the program. All uncaught exceptions in a method that are not instances of RuntimeException
must be declared using the throws
keyword.
;transient
ECHELON, originally a secret government code name, is a surveillance program ( signals intelligence/SIGINT collection and analysis network) operated by the five signatory states to the UKUSA Security Agreement:Given the 5 dialects that ...
:Declares that an instance field is not part of the default serialized form of an object. When an object is serialized, only the values of its non-transient instance fields are included in the default serial representation. When an object is deserialized, transient fields are initialized only to their default value. If the default form is not used, e.g. when a ''serialPersistentFields'' table is declared in the class hierarchy, all transient
keywords are ignored.
;try
Try or TRY may refer to:
Music Albums
* ''Try!'', an album by the John Mayer Trio
* ''Try'' (Bebo Norman album) (2014) Songs
* "Try" (Blue Rodeo song) (1987)
* "Try" (Colbie Caillat song) (2014)
* "Try" (Nelly Furtado song) (2004)
* " Try (Ju ...
:Defines a block of statements that have exception handling. If an exception is thrown inside the try
block, an optional catch
block can handle declared exception types. Also, an optional finally
block can be declared that will be executed when execution exits the try
block and catch
clauses, regardless of whether an exception is thrown or not. A try
block must have at least one catch
clause or a finally
block.
;void
Void may refer to:
Science, engineering, and technology
* Void (astronomy), the spaces between galaxy filaments that contain no galaxies
* Void (composites), a pore that remains unoccupied in a composite material
* Void, synonym for vacuum, a s ...
:The void
keyword is used to declare that a method does not return any value.
; volatile
:Used in field declarations to guarantee visibility of changes to variables across threads. Every read of a volatile variable will be read from main memory, and not from the CPU cache, and that every write to a volatile variable will be written to main memory, and not just to the CPU cache. Methods, classes and interfaces thus cannot be declared ''volatile'', nor can local variables or parameters.
; while
:The while
keyword is used to create a true
; this continues until the expression evaluates to false
. This keyword can also be used to create a do-while loop; see '' do
''.
Reserved Identifiers
The following identifiers are contextual keywords, and are only restricted in some contexts:exports
module
;non-sealed
:Used to declare that a class or interface which extends a sealed class can be extended by unknown classes.
;open
;opens
;permits
:The permits clause specifies the classes that are permitted to extend a sealed class.
;provides
;record
requires
;sealed
:A sealed class or interface can only be extended or implemented by classes and interfaces permitted to do so.
;to
;transitive
;uses
;var
:A special identifier that cannot be used as a type name (since Java 10).
;with
;yield
:Used to set a value for a switch expression, when using labelled statement groups (for example, case L:
).
Reserved words for literal values
;true
True most commonly refers to truth, the state of being in congruence with fact or reality.
True may also refer to:
Places
* True, West Virginia, an unincorporated community in the United States
* True, Wisconsin, a town in the United States
* Tr ...
:A boolean literal value.
; false
:A boolean literal value.
;null
Null may refer to:
Science, technology, and mathematics Computing
*Null (SQL) (or NULL), a special marker and keyword in SQL indicating that something has no value
*Null character, the zero-valued ASCII character, also designated by , often used ...
:A reference literal value.
Unused
;const
In some programming languages, const is a type qualifier (a keyword applied to a data type) that indicates that the data is read-only. While this can be used to declare constants, in the C family of languages differs from similar constructs in ...
:Although reserved as a keyword in Java, const
is not used and has no function. For defining constants in Java, see the final
keyword.
;goto
GoTo (goto, GOTO, GO TO or other case combinations, depending on the programming language) is a statement found in many computer programming languages. It performs a one-way transfer of control to another line of code; in contrast a function ca ...
:Although reserved as a keyword in Java, goto
is not used and has no function.
;strictfp
strictfp is an obsolete and unused reserved word in the Java programming language. Previously, this keyword was used as a modifier that restricted floating-point calculations to IEEE 754 semantics in order to ensure portability. The strictfp keywor ...
(added in strictfp
is obsolete, and no longer has any function. Previously this keyword was used to restrict the precision and rounding of floating point calculations to ensure portability.
See also
*References
External links
* * {{Refend Java (programming language) Java keywords