Keywords or Reserved words are the words in a language that are used for some internal process or represent some predefined actions. These words are therefore not allowed to use as a variable names or objects. Doing this will result into a compile time error.

Java also contains a list of reserved words or keywords. These are:

• abstract -Specifies that a class or method will be implemented later, in a subclass
• assert -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.
• boolean – A data type that can hold True and False values only
• break – A control statement for breaking out of loops
• byte – A data type that can hold 8-bit data values
• case – Used in switch statements to mark blocks of text
• catch – Catches exceptions generated by try statements
• char – A data type that can hold unsigned 16-bit Unicode characters
• class -Declares a new class
• continue -Sends control back outside a loop
• default -Specifies the default block of code in a switch statement
• do -Starts a do-while loop
• double – A data type that can hold 64-bit floating-point numbers
• else – Indicates alternative branches in an if statement
• enum – A Java keyword used to declare an enumerated type. Enumerations extend the base class.
• extends -Indicates that a class is derived from another class or interface
• final -Indicates that a variable holds a constant value or that a method will not be overridden
• finally -Indicates a block of code in a try-catch structure that will always be executed
• float -A data type that holds a 32-bit floating-point number
• for -Used to start a for loop
• if -Tests a true/false expression and branches accordingly
• implements -Specifies that a class implements an interface
• import -References other classes
• instanceof -Indicates whether an object is an instance of a specific class or implements an interface
• int – A data type that can hold a 32-bit signed integer
• interface – Declares an interface
• long – A data type that holds a 64-bit integer
• native -Specifies that a method is implemented with native (platform-specific) code
• new – Creates new objects
• null -Indicates that a reference does not refer to anything
• package – Declares a Java package
• private -An access specifier indicating that a method or variable may be accessed only in the class it’s declared in
• protected – An access specifier indicating that a method or variable may only be accessed in the class it’s
• declared in (or a subclass of the class it’s declared in or other classes in the same package)
• public – An access specifier used for classes, interfaces, methods, and variables indicating that an item is accessible throughout the application (or where the class that defines it is accessible)
• return -Sends control and possibly a return value back from a called method
• short – A data type that can hold a 16-bit integer
• static -Indicates that a variable or method is a class method (rather than being limited to one particular object)
• strictfp – A Java keyword used to restrict the precision and rounding of floating point calculations to ensure portability.
• super – Refers to a class’s base class (used in a method or class constructor)
• switch -A statement that executes code based on a test value
• synchronized -Specifies critical sections or methods in multithreaded code
• this -Refers to the current object in a method or constructor
• throw – Creates an exception
• throws -Indicates what exceptions may be thrown by a method
• transient -Specifies that a variable is not part of an object’s persistent state
• try -Starts a block of code that will be tested for exceptions
• void -Specifies that a method does not have a return value
• volatile -Indicates that a variable may change asynchronously
• while -Starts a while loop

** The keywords const and goto are reserved, even they are not currently in use.

• const -Reserved for future use
• goto – Reserved for future use

** true, false and null look like keywords, but in actual they are literals. However they still can’t be used as identifiers in a program.