Keywords in java

Keywords

Keywords are identifiers like public, static and class that have a special meaning inside Java source code and outside of comments and Strings. Four keywords are used in Hello World, public, static,void and class.



Keywords are reserved for their intended use and cannot be used by the programmer for variable or method names.
There are fifty reserved keywords in Java 1.1, 51 in Java 1.2, 52 in Java 1.4, and 54 in Java 5. The forty-eight that are actually used in are listed below. Don't worry if the purposes of the keywords seem a little opaque at this point. They will all be explained in much greater detail later.

Keywords Used in Java 1.1

Keyword	Purpose
boolean	declares a boolean variable or return type
byte	declares a byte variable or return type
char	declares a character variable or return type
double	declares a double variable or return type
float	declares a floating point variable or return type
short	declares a short integer variable or return type
void	declare that a method does not return a value
int	declares an integer variable or return type
long	declares a long integer variable or return type
while	begins a while loop
for	begins a for loop
do	begins a do while loop
switch	tests for the truth of various possible cases
break	prematurely exits a loop
continue	prematurely return to the beginning of a loop
case	one case in a switch statement
default	default action for a switch statement
if	execute statements if the condition is true
else	signals the code to be executed if an if statement is not true
try	attempt an operation that may throw an exception
catch	handle an exception
finally	declares a block of code guaranteed to be executed
class	signals the beginning of a class definition
abstract	declares that a class or method is abstract
extends	specifies the class which this class is a subclass of
final	declares that a class may not be subclassed or that a field or method may not be overridden
implements	declares that this class implements the given interface
import	permit access to a class or group of classes in a package
instanceof	tests whether an object is an instanceof a class
interface	signals the beginning of an interface definition
native	declares that a method is implemented in native code
new	allocates a new object
package	defines the package in which this source code file belongs
private	declares a method or member variable to be private
protected	declares a class, method or member variable to be protected
public	declares a class, method or member variable to be public
return	returns a value from a method
static	declares that a field or a method belongs to a class rather than an object
super	a reference to the parent of the current object
synchronized	Indicates that a section of code is not thread-safe
this	a reference to the current object
throw	throw an exception
throws	declares the exceptions thrown by a method
transient	This field should not be serialized
volatile	Warns the compiler that a variable changes asynchronously

Two other keywords, const and goto, are reserved by Java but are not actually implemented. This allows compilers to produce better error messages if these common C++ keywords are improperly used in a Java program.
Java 1.2 adds the strictfp keyword to declare that a method or class must be run with exact IEEE 754 semantics.

Java 1.4 adds the assert keyword to specify assertions.

Java 5 adds assert and enum.

true and false appear to be missing from this list. In fact, they are not keywords but rather boolean literals. You still can't use them as a variable name though.