appendix A

Language Summary

by Laura Lemay

CONTENTS

Reserved Words
Comments
Literals
Variable Declaration
Variable Assignment
Operators
Objects
Arrays
Loops and Conditionals
Class Definitions
Method and Constructor Definitions
Packages, Interfaces, and Importing
Exceptions and Guarding

This appendix contains a summary or quick reference for the Java language, as described in this book.

Technical Note

This is not a grammar overview, nor is it a technical overview of the language itself. It's a quick reference to be used after you already know the basics of how the language works. If you need a technical description of the language, your best bet is to visit the Java Web site (http://java.sun.com) and download the actual specification, which includes a full BNF grammar.

Language keywords and symbols are shown in a monospace font. Arguments and other parts to be substituted are in italic monospace.

Optional parts are indicated by brackets (except in the array syntax section). If there are several options that are mutually exclusive, they are shown separated by pipes ([|]) like this:

[ public | private | protected ] type varname

Reserved Words

The following words are reserved for use by the Java language itself (some of them are reserved but not currently used). You cannot use these words to refer to classes, methods, or variable names:

`abstract`	float	public
`boolean`	for	return
`break`	goto	short
`byte`	if	static
`case`	implements	super
`catch`	import	switch
`char`	instanceof	synchronize
`class`	int	this
`const`	interface	throw
`continue`	long	throws
`do`	native	transient
`double`	new	try
`else`	null	void
`extends`	packa	volatilege
`final`	private	while
`finally`	protected

Comments

/* this is a multiline comment */
// this is a single-line comment
/** Javadoc comment */

Literals

`number`	Type int
`number[l \| L]`	Type long
`0xhex`	Hex integer
`0Xhex`	Hex integer
`0octal`	Octal integer
`[ number ].number`	Type double
`number[ f \| f]`	Type float
`number[ d \| D]`	Type double
`[ + \| - ] number`	Signed
`numberenumber`	Exponent
`numberEnumber`	Exponent
`'character'`	Single character
`"characters"`	String
`""`	Empty string
`\b`	Backspace
`\t`	Tab
`\n`	Line feed
`\f`	Form feed
`\r`	Carriage return
`\"`	Double quote
`\'`	Single quote
`\\`	Backslash
`\uNNNN`	Unicode escape (NNNN is hex)
`true`	Boolean
`false`	Boolean

Variable Declaration

`[ byte \| short \| int \| long ] varname`	Integers (pick one type)
`[ float \| double ] varname`	Floats (pick one type)
`char varname`	Characters
`boolean varname`	Boolean
`classname varname`	Class types
`interfacename varname`	Interface types
`type varname, varname, varname`	Multiple variables

The following options are available only for class and instance variables. Any of these options can be used with a variable declaration:

`[ static ] variableDeclaration`	Class variable
`[ final ] variableDeclaration`	Constants
`[ public \| private \| protected ] variableDeclaration`	Access control
`[volatile] varname`	Modified asynchronously
`[transient] varname`	Not persistent (not yet implemented)

Variable Assignment

`variable = value`	Assignment
`variable++`	Postfix increment
`++variable`	Prefix increment
`variable--`	Postfix decrement
`--variable`	Prefix decrement
`variable += value`	Add and assign
`variable -= value`	Subtract and assign
`variable *= value`	Multiply and assign
`variable /= value`	Divide and assign
`variable %= value`	Modulus and assign
`variable &= value`	AND and assign
`variable \|= value`	OR and assign
`variable ^= value`	XOR and assign
`variable <<= value`	Left-shift and assign
`variable >>= value`	Right-shift and assign
`variable >>>= value`	Zero-fill right-shift and assign

Operators

`arg + arg`	Addition
`arg - arg`	Subtraction
`arg * arg`	Multiplication
`arg / arg`	Division
`arg % arg`	Modulus
`arg < arg`	Less than
`arg > arg`	Greater than
`arg <= arg`	Less than or equal to
`arg >= arg`	Greater than or equal to
`arg == arg`	Equal
`arg != arg`	Not equal
`arg && arg`	Logical AND
`arg \|\| arg`	Logical OR
`! arg`	Logical NOT
`arg & arg`	AND
`arg \| arg`	OR
`arg ^ arg`	XOR
`arg << arg`	Left-shift
`arg >> arg`	Right-shift
`arg >>> arg`	Zero-fill right-shift
`~ arg`	Complement
`(type)thing`	Casting
`arg instanceof class`	Instance of
`test ? trueOp : falseOp`	Ternary (if) operator

Objects

`new class()`	Creates new instance
`new class(arg,arg,arg...)`	New instance with parameters
`object.variable`	Instance variable
`object.classvar`	Class variable
`Class.classvar`	Class variable
`object.method()`	Instance method (no args)
`object.method(arg,arg,arg...)`	Instance method
`object.classmethod()`	Class method (no args)
`object.classmethod(arg,arg,arg...)`	Class method
`Class.classmethod()`	Class method (no args)
`Class.classmethod(arg,arg,arg...)`	Class method

Arrays

Note

The brackets in this section are parts of the array creation or access statements. They do not denote optional parts as they do in other parts of this appendix.

`Type varname[]`	Array variable
`type[] varname`	Array variable
`new type[numElements]`	New array object
`array[index]`	Element access
`array.length`	Length of array

Loops and Conditionals

`if ( test) block`	Conditional
`if ( test ) block else block`	Conditional with else
switch (test) { `case value : statements` `case value : statements` `...` `default : statement }`	switch (only with integer or char types)
`for (initializer; test; change ) block`	for loop
`while ( test ) block`	while loop
`do block` `while (test)`	do loop
`break [ label ]`	break from loop or switch
`continue [ label ]`	continue loop
`label:`	Labeled loop

Class Definitions

`class classname block`	Simple class definition
Any of the following optional modifiers can be added to the class definition:
`[ final ] class classname block`	Cannot be subclassed
`[ abstract ] class classname block`	Cannot be instantiated
`[ public ] class classname block`	Accessible outside package
`class classname [ extends Superclass ] block`	Define superclass
`class classname [ implements interfaces ] block`	Implement one or more interfaces

Method and Constructor Definitions

The basic method looks like this, where returnType is a type name, a class name, or void.

`ReturnType methodName() block`	Basic method
`returnType methodName(parameter, parameter, ...) block`	Method with parameters

Method parameters look like this:

type parameterName

Method variations can include any of the following optional keywords:

`[ abstract ] returnType methodName() block`	Abstract method
`[ static ] returnType methodName() block`	Class method
`[ native ] returnType methodName() block`	Native method
`[ final ] returnType methodName() block`	`final method`
`[ synchronized ] returnType methodName() block`	Thread lock before executing
`[ public \| private \| protected ] returnType methodName()`	Access control

Constructors look like this:

`classname() block`	Basic constructor
`classname(parameter, parameter, parameter...) block`	Constructor with parameters
`[ public \| private \| protected] classname() block`	Access control

In the method/constructor body you can use these references and methods:

`this`	Refers to current object
`super`	Refers to superclass
`super.methodName()`	Calls a superclass's method
`this(...)`	Calls class's constructor
`super(...)`	Calls superclass's constructor
`return [ value ]`	Returns a value

Packages, Interfaces, and Importing

`import package.className`	Imports specific class name
`import package.*`	Imports all public classes in package

package packagename Classes in this file belong to this package

interface interfaceName [ extends anotherInterface ] block

[ public ] interface interfaceName block

[ abstract ] interface interfaceName block

Exceptions and Guarding

synchronized ( object ) block Waits for lock on object

`try block`	Guarded statements
`catch ( exception ) block`	Executed if exception is thrown
`[ finally block ]`	Cleanup code

try block [ catch ( exception ) block ] finally block Same as previous example (can use optional catch or finally, or both)