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Reserved Words

 

Keywords are identifiers like public, static, and class that have a special meaning inside
Java source code and outside of comments and Strings.
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). The forty-eight that are
actually used in are listed below.
 
Keywords Used in Java 1.1 (separate page on this)
abstract
declares that a class or method is abstract
boolean
declares a boolean variable or return type
break
prematurely exits a loop
byte
declares a byte variable or return type
case
one case in a switch statement
catch
handle an exception
char
declares a character variable or return type
class
signals the beginning of a class definition
continue
prematurely return to the beginning of a loop
default
default action for a switch statement
do
begins a do while loop
double
declares a double variable or return type
else
signals the code to be executed if an if statement is not true
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
finally
declares a block of code guaranteed to be executed
float
declares a floating point variable or return type
for
begins a for loop
if
execute statements if the condition is true
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
int
declares an integer variable or return type
interface
signals the beginning of an interface definition
long
declares a long integer variable or return type
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
short
declares a short integer variable or return type
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
switch
tests for the truth of various possible cases
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
try
attempt an operation that may throw an exception
void
declare that a method does not return a value
volatile
Warns the compiler that a variable changes asynchronously
while
begins a while loop
 
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.
 
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.