APPENDIX A

RULEBOOK

After we study any language, we are not in a position to remember every thing. Therefore, a quick ready reference becomes very useful. In the following table, we have tried to summarize all the important rules, points, and facts about Java programming. If you get some errors and want to get some clue quickly without reading the entire text, the following table will be of great help to you.

Keyword	The rule
abstract class	A class containing an abstract method is an abstract class. Such a class must be explicitly declared as abstract.
abstract class	An abstract class cannot be instantiated.
abstract class extending	If a class extends an abstract class, it must define all the methods of the super class. Otherwise, it has to be declared abstract.
abstract method	A method declared without the body is an abstract method. Such a method has to be declared as Abstract
add	The add method for attaching GUI components is a Container class method and not of Component class.
Applet writing to disk	Java does not allow applets to write to local disk.
Applet class	The Applet class must be the super class of any applet that is to be embedded in a Web page or viewed by the Java Applet Viewer.
applet i/o	User I/O is not accomplished with Java’s stream I/O classes.
applet i/o	User I/O is accomplished with AWT or swing objects
applet main()	Applets do not need a main() method.
APPLET tag	The APPLET tag is used to start an applet from both an HTML document and from an applet viewer.
array index checking	Java checks array index during runtime. If program tries to use index out of bound, a runtime error occurs.
array size	When an array size (dimension) is specified, it cannot be changed later in the program.
arrays methods	Arrays are passed to methods by call-by-reference.
Assignment	You can assign a character variable to integer but not vice versa
Bit-wise operator	Bit-wise operators accept only integral operands (char, byte, short, int, and long). Float and double are not allowed.
Boolean type	The Boolean type cannot be converted from or to any other data type.
Boolean variable	In Java, Boolean variable does not take the value 1 or 0; it takes true or false values only.
break	A break statement can be used only within loop or switch case statements.
Bytecode	The type of code generated by a Java compiler
Character constant	Character constant (literal) is formed by enclosing a single character in pair of single quotes.
Checked Exceptions	Only runtime exceptions (including its subclasses) are checked exceptions; all others are unchecked exceptions.
Cloneable, Comparable and Runnable	Interfaces defined by java.lang are Cloneable, Comparable, and Runnable.
Cloneable	A Cloneable interface defines no members.
Collection framework	Components of “Collection framework” are available in the package java.util
Comma operator	Java does not support the comma operator (of C++).
command line arguments	All command line arguments are passed as a string to method main.
Comments	Comments increase the readability of the program.
Comments	Comments have no relevance to program (execution) speed.
const	In Java const is a reserved word, reserved for future use.
constructor	Constructors do not have a return type.
constructor	Name of the constructor is same as that of the class.
constructor	Constructors can be overloaded.
constructor	A class constructor may have public or protected keyword before them, nothing else.
constructor	constructor is a method is used to initialize the instance variable of a class.
container event	Container event class is generated when a component is added to or removed from a container.
cv for	The control variable declared in for loop is visible only within the scope of the loop. But in C/C++, it is visible even after the loop is exited.
Default constructor	If class definition does not contain a constructor, the compiler provides a default constructor which initializes all data members to null values.
do-while	do-while loop construct will always be executed at least once.
escape codes	In Java, there are no escape codes defined for vertical tab and the bell character.
Exception	An Exception is an abnormal condition that disrupts normal program flow.
Exception class	The root class of all the exception classes is the Exception class.
expression statement	Only certain types of expressions are allowed in expression statement. They are assignment, inc/dec, and method call.
Expressions	Expressions are combinations of variables, keywords or symbols that evaluate to a value of some type.
final	A final variable cannot change from its initialized value.
final class	A class declared final cannot be sub-classed.
final method	A method declared as final cannot be overridden.
finalize()	Method finalize() is called before an unused object is recycled.
finally	When a finally block is present, it is always executed irrespective of occurrence of exception.
finally	A finally block is optional.
for loop	The second expression in for statement must be a Boolean expression. As a special case, it can be a blank expression which is considered as having value “true”.
functions	Every function in Java must be a member of some class. Java uses term method for such member functions.
Garbage collection	When all references to an object are gone, the memory used by the object is automatically reclaimed.
graphics	Graphic class is defined in java.awt package.
Implements	A class can use an interface by using the Implements clause.
import	Java by default imports package java.lang. We do not have to import it specifically.
import statement	Import statement must come before all other statements except package statement.
in	The object “in” belongs to class InputStream. It is standard input stream.
in, out, err	In, out, and err are predefined stream variables.
Inheritance	Inheritance is a mechanism that enables one class to inherit in general the behavior and attributes of another class. But we cannot say that it inherits all the behavior and attributes.
Initialization	Initialization can happen only ones in the applets lifetime. However, currently this rule has changed.
initialization of class variable	JVM automatically initializes every numeric instance of class variable.
inner	Objects declared within the inner scope will not be visible outside it
inputStream	Abstract class inputStream is the super class of all classes used for reading bytes.
Instantiation exception	Instantiation exception means an attempt to create an abstract class or interface.
interface	A class can have more than one interface.
interface	An interface can extend any number of interfaces,
Java-compatible browser	Applets should be run under a Java-compatible browser.
Javax.swing	Javax.swing is the high-level swing package, and primarily consists of components, adapters, default component models and interfaces for all the delegates and models.
Join()	The join() method suspends the current thread until that thread object dies.
Jpanel	Jpanel is a Container.
Key events	Key events are generated when a user presses or releases a key on the keyboard.
keywords currently in use
keywords which are values defined	false      null      true
keywords reserved for future use	const      goto
labelled break labelled continue	Labelled break and labelled continue statements are allowed in Java.
labeled break labeled continue	Labelled break and labelled continue statements must be inside the loop so labelled.
long	The number of bytes used by Java primitive long is 8.
main()	Java applications begin execution at method main().
Main()	Main() is a class method, not an object method.
method interface	Methods declared in interface must be declared public in class definition.
method interface	Any normal class (non Abstract) must fully define all the methods declared in the interface.
modulo division	Modulo divisor operator can be used with floating point values in Java. This is not allowed in C/C++.
monitor	The sleep() method tells the calling thread to give up monitor until some other thread enters the same monitor.
multiple inheritance	Java does not allow multiple inheritances, where a class has more than one super class.
multiple inheritances	Java allows multiple inheritances by means of interfaces.
multiple listeners	A component can have multiple listeners for events of different type.
native	The native keyword indicates that the method is implemented in another language like C/C++.
NORM_PRIORITY	NORM_PRIORITY is the default priority of a newly created thread.
object class	By default, classes inherit from the Object class, which is a super class of all classes in the Java class hierarchy.
out	The object out” belongs to class printStream. It is standard output stream.
overloading	A method with a given name in a class can have different signatures. Such methods are said to be overloaded.
overloading	A method in a class cannot have two definitions with same signature, even if return types are different.
override	A method is overridden when another method with the same signature is declared in a subclass.
override	A final method cannot be overridden
package statement	If any program contains package statement, it has to be the first statement.
parameter passing	Basic parameter passing in Java is call-by-value. All simple types are passed by call-by-value. However, all aggregate types effectively get passed by call-by-reference
parseInt	The method is used to convert String to an integer, assuming that the String represents an integer.
preemptive switching	A thread priority is used to decide when to move from one running thread to the next. This is called preemptive switching.
program file name	A simple Java application source file must have extension java. The name of the file and the name of the public class must be identical (case sensitive)
RadioButtons	RadioButtons are implemented in swing through the JRadioButtons class.
Reader	Abstract class Reader is the super class of all classes used for reading characters.
Relational expressions	Relational expressions return Boolean value. Note: C++ returns int.
return statement	If return type of a method is void, return statement is optional. For any other return type, it is compulsory.
Set	Set is a collection interface used to maintain unique elements.
Sleep()	The sleep() method is used to temporarily stop the execution of the thread.
source file public class	If a source file includes a public class, the class name must match the unextended filename. In other words, there cannot be two public classes in a single source file.
Stack overflow Runtime exception	Stack overflow is an example of Runtime exception.
Start()	After the start() method is called, the thread is in a Runnable state.
static for local variables.	Keyword static not allowed for local variables of any method.
static method	A static method cannot make a reference to non-static variables of a class.
static method	When a method is made static, it cannot use keywords this or super.
static variable	A static variable indicates that there is only one copy of that variable.
String operators	Strings cannot be lexicographically compared using operators like > or <= .
string constant	String constant (literal) is formed by enclosing a zero or more characters in pair of double quotes.
String immutable	Strings in Java are immutable, meaning they cannot be changed. The methods which appear to modify a given string actually return a new (separate) string.
StringBuffer	When no specific buffer length is requested, StringBuffer allocates room for 16 additional characters.
StringBuffer mutable	Objects of class StringBuffer are very much like strings. However, they are mutable (can be modified).
sub-class variable	Sub-class reference variable cannot be assigned a super-class reference value
sub-class constructor	Every constructor of a sub class must have a call to super class constructor as a first statement. Only exception is when super-class has no constructor or has a default constructor (one without parameters).
super-class variable	Super-class reference variable can be assigned a sub-class reference value
switch default	Default clause is optional in Java
switch expression	Switch expression can be of basic type byte, short, int, or char. It can be also be Wrapper class type like Character, Byte, Short, or Integer. It can be also of any enumerated type.
synchronized	Every object that has synchronized methods has a monitor.
thread class	By using a thread class, multithreaded program can be created.
Thread priority	Threads may yield to threads of lower priority.
Thread simultaneous access	It is possible for two threads to access the same variable or the same method of same object at same time. However, the net result will be unpredictable.
throw	A throw statement causes an exception to be thrown.
throws	A special clause called throws is used in method definition to indicate that a method may possibly throw an exception.
trim()String	String method trim() returns a new String object in which all white-space characters have been removed from the beginning and end of a string.
try	A try block must be followed by a catch block. Catch block need not be present if finally block is present.
Unicode character	Unicode character can be expressed as u followed by four hexadecimal digits. Note character u is in lowercase. There must be exactly four digits no more any less.
Unsigned	Integer types are always signed in Java. There is no unsigned qualifier in Java.
variable initialization	Java flags compilation error if one tries to use ordinary variables without initialization.
variable name	A variable name can contain as well as start with character $.
variables interface	Variables in interface must be declared as final.
Vector	Elements of the vector can only be objects. Simple data types like integers are not allowed as elements.
Vector size()	The size() method determines the number of elements in Vector (not sizeOf() ).
void	In Java if method does not return any value, then it must be declared as void.
Web page	To change Web page background colours, use the BGCOLOR attribute in the <BODY> tag.
Writer	Abstract class Writer is the super-class of all classes used for writing characters.