keywords.md

Java keywords

Keywords in Java are reserved words that represent predefined actions, internal processes.

Control Statements

Name	Syntax
if	if(condition) Statement(s); else statment(s);
for	for(initialization; condition; iteration) statement(s);
for-each	for(type itr-var : collection) statement(s);
switch	switch(expression) { case value1: //statement(s) break; . . case value(n): //statement(s) break; default: //default statement(n) }
while	while(condition) { //body of loop }
do-while	do { //body of loop } while(condition);

Jump statements

Name	Description
break	Use to terminate loop, switch statement, goto statement(break label;).
continue	Useful to force an early iteration of a loop.
return	Use to explicitly return from the method, control transfer back to the caller of the method.

Data types

Primitive types

Name	Group/Width	Syntax	Range
byte	integer/8-bit	byte variable_name = value;	-128 - 127
short	integer/16-bit	int variable_name = value;	-32768 - 32767
int	integer/32-bit	int variable_name = value;	-2147483648 - 2147483647
long	integer/64-bit	long variable_name = value;	-9223372036854775808 - 9223372036854775807
float	floating point/32-bit	float variable_name = valuef;	1.4e-045 - 3.4e+038
double	floating point/64-bit	double variable_name = value;	4.9e-324 - 1.8e+308
char	characters/16-bit	char variable_name = 'value';	0 - 65536
boolean	boolean	boolean variable_name = true/false;	true - false

Inheritance

Syntax	Description
extends	extends keyword simply incorporate the definition of one class into another(can't access private members).
super	subclass can call a constructor defined by its superclass by use of super(arg-list);, it also acts like this keyword like super.member;
abstract	abstract class cann't be used to create object, it must be inherited from one class to another. abstract method can only be used in abstract class, it is undefined(no body), body is placed in subclass.
interface	use to fully abstract a class, what a class can do & how it does, they lack instance variables, also their methods are declared without any body. Any number of classes can implement interface & vise versa. Variables declared are implicitly final, static & public.
implements	interface can be implemented on more than one class. Include implements clause in class definition like: class class-name implements interface-name. For more than one interface use comma to separate. To implement an interface method, it must be declared as public. If a class includes an interface but does not fully implement the methods then that class must be declared as abstract.
default	default method provide a means by which interfaces could be expanded without breaking existing code.

Other keywords

Syntax	Description
main	java program begins execution by calling main().
public	it is used when code line is to be used outside the class.
private	prevents member to be used outside the class.
static	a static member can be accessed before any objects of its class are created, & without reference to any object.
void	tells the compiler that main() does not return a value.
var	reserved type-name, auto tells type of variable, also act as identifier, can be used with arrays (brackets[] should only be used by type not with var in arrays).
String	String defines an object, used to declare string variables, simply String var-name = "value"; (example).
new	it dynamically allocates memory for an object.
this	it is used inside any method to refer to the current object.
final	a final member can't be modified, making it a constant. final member must be initialized when it is declared. Methods declared as final also cann't be overriden. class declared as final cann't be inherited.
Object	Object is a superclass of all other classes, a reference variable of type Object can refer to an object of any other class.
package	package pkg; (syntax) statement defines a name space in which your classes are stored. For multilevel package, we use hierarchy of packages like: package pkg1.pkg2.pk3;
import	statement use to bring certain classes, or entire packages, into visibility. Generally like: import pkg1.pkg2.classname |*.
Runnable	it abstracts a unit of executable code, a thread can be constructed on any object that implements Runnable.
synchronized	it is used to lock a single thread with the shared data so that no other thread can access it. While a synchronized block is synchronized on some object.

Exception handler

Syntax	Description
try	use to enclose the code that you want to monitor inside a block.
catch	a clause that specifies the exception type that you wish to catch.
throw	use to throw an exception explicitly.
throws	a throws clause lists the types of exceptions that a method might throw.
finally	finally creates a block of code that will be executed after a try/catch block has completed & before the code following the try/catch block.

Separators

Symbol	Purpose
()	contain list of parameters.
{}	define a block of code.
[]	declare array types.
;	terminate a statement.
,	separation in variable declaration.
.	separate package names.
::	create method or constructor reference.
...	indicates variable-arity parameter.
@	begins an annotation.

Escape sequences

Symbol	Description
\ddd	octal character
\uxxxx	hexadecimal unicode character
\'	single quote
\"	double quote
\\	backslash
\r	carriage return
\n	new line
\f	form feed
\t	tab
\b	backspace

Arithmetic operators

Operator	Result
+	Addition
-	Subtraction
*	Multiplication
/	Division
%	Modulus
++	Increment
+=	Addition assignment
-=	Subtraction assignment
*=	Multiplication assignment
/=	Division assignment
%=	Modulus assignment
--	Decrement

Bitwise operators

Operator	Result
~	NOT
&	AND
|	OR
^	exclusive OR
>>	Shift right
>>>	Shift right zero fill
<<	Shift left
&=	AND assignment
|=	OR assignment
^=	exclusive OR assignment
>>=	Shift right assignment
>>>=	Shift right zero fill assignment
<<=	Shift left assignment

Object class methods

Method	Purpose
Object clone()	creates a new object that is same as the object being cloned.
boolean equal(Object object)	determine wheather one object is equal to another.
void finalize()	called before an unused object is recycled.
Class<?>getClass()	obtains the class of an object at run time.
int hashCode()	returns the hash code associated with the invoking object.
void notify()	resumes execution of a thread waiting on the invoking object.
void notifyAll()	resumes execution of all thread waiting on the invoking object.
String toString()	returns a string that describes the object.
void wait() void wait(long milliseconds) void wait(long milliseconds, nanoseconds)	waits on another thread of execution.

Thread class methods

Method	Meaning
getName	obtain a thread's name.
getPriority	obtain a thread's priority.
isAlive	determine if a thread is still runnung.
join	wait for a thread to terminate.
run	entry point for the thread.
sleep	suspend a thread for a period of time.
start	start a thread by calling its run method.