1.02 Reserved Words

In Java some words are reserved to represent some meaning or functionality such type of words are called Reserved Words

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

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NOTE 01

1. In java return type is mandatory, if a method doesn’t return anything then we have to declare the method with void return type.
2. Usage of goto created several problems hence it is banned in Java.
3. Use final instead of const
4. The keywords const and goto are reserved, even they are not currently in use.
5. We can use enum to define a group of named constants.

Example of enum:

enum month {
    JAN,FEB,MAR,APR,MAY,JUN,JUL,AUG,SEPT,OCT,NOV,DEC
}

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Conclusions

1. All 53 reserved words contains lower-case alphabets only instanceof, strictfp
2. In Java we have only new keyword and there is no delete keyword because destruction of useless objects is the responsibility of Garbage Collector.

3. The following are newly added Keywords in Java:

   • strictfp
   • assert
   • enum

NOTE 02

1. strictfp but not strictFp
2. instanceof but not instanceOf
3. synchonized but not synchronise
4. extends but not extend
5. implements but not implement
6. import but not imports
7. const but not constant

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TEST

Q. Which of the following lists contains only Java reserved words?

Sr. No.	word
1.	new, delete
2.	goto constant
3.	break, continue, return, exit
4.	final, finally, finalize
5.	throw, throws, thrown
6.	notify, notifyAll
7.	implements, extends, imports
8.	sizeof, instanceof
9.	instanceOf, strictFp
10.	byte, short, Int
11.	None of Above

Answers

Sr. No.	word	Answer
1.	new, delete	delete is not a keyword in Java
2.	goto, constant	const is keyword, constant is not a keyword
3.	break, continue, return, exit	exit is not a keyword in Java (Method)
4.	final, finally, finalize	finalize is not a keyword in Java
5.	throw, throws, thrown	thrown is not a Keyword in Java
6.	notify, notifyAll	both are not Java Keywords. (Methods)
7.	implements, extends, imports	imports is not a Java Keywords
8.	sizeof, instanceof	sizeof is not a Java Keyword
9.	instanceOf, strictFp	Java keywords contain lower-case alphabets only
10.	byte, short, Int	Java keywords contain lower-case alphabets only
11.	None of Above	Solution: No list contains Java keywords only.

Q. Which of the following are Java reserved words?

public, static, void, main, String, args :
First three only. String is a ‘pre-defined’ class name.

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