Java Practices->Home

javapractices.com offers concise presentations of Java practices, tasks, and designs, illustrated with syntax-highlighted code examples. Some general-purpose references are provided, along with some source code. See below for user comments on the site.

Simplicity does not precede complexity, but follows it. - Alan Perlis, Epigrams In Programming

Constructors

Constructors in general	Construct Object using class name
Copy constructors	Initializing fields to 0 false null is redundant
Beware of mistaken field redeclares	Constructors shouldn't call overridables
Don't pass 'this' out of a constructor	Constructors shouldn't start threads
Avoid JavaBeans style of construction

Overriding Object Methods

Implementing compareTo	Implementing equals
Never rely on finalize	Implementing hashCode
Implementing toString	Avoid clone

Inheritance

Designing for subclassing	Consider composition instead of subclassing
Overridable methods need special care	Remember styles of inheritance

Assertions

Assert is for private arguments only	Assertions in general
Assert use cases	Force enabling of assertions

Collections

Ways of iterating	Encapsulate collections
Use for each liberally	Use interface references to Collections
Remove from a collection	Prefer Collections over older classes
Choosing the right Collection	Iterate without an index
Use standard Collections

Exceptions

Exception translation	Checked versus unchecked exceptions
Pass all pertinent data to exceptions	Avoid empty catch blocks
Avoid @throws in javadoc	Exceptions and control flow
Use template for repeated try catch	Beware of unknown root causes
Finally and catch	Be specific in throws clause
Javadoc all exceptions	Stack trace as String

Input Output

Buffering usually appropriate	Reading and writing binary files
Copy a file	Delete a directory tree
Copy a directory tree	Reading and writing text files
Reading and writing Serializable objects	Recursive file listing
Console input	Always close streams

Serialization

Some classes need readResolve	Implementing Serializable
Serialization and subclassing

Threads

Data integrity first	Read write locks
Perform N tasks in parallel	Prefer modern libraries for concurrency
Query host for the number of processors	Always shut down an ExecutorService
Handle InterruptedException	Use finally to unlock
Dump thread information	Remember the types of intrinsic lock
Stop threads through cooperation	Document thread safety
Synchronize access to mutable fields	Launch thread is just another user thread
Objects communicating across threads	Avoid ThreadGroup
Thread priorities are not portable	Schedule periodic tasks
Synchronized is implementation detail

Common Practices

Compile regular expressions once	Multiple return statements
Coding conventions	Overloading can be tricky
Minimize ripple effects	Don't declare local variables before use
Consider code generators	Avoid null if possible
Separate public and private members	Defensive copying
Test using main method	Use enums to restrict arguments
Design by Contract	Use static imports rarely
Use boxing with care	Class for constants
Extra space in argument list	Quote dynamic text when logging
Package by feature, not layer	Try alternatives to ResourceBundle
Validation belongs in a Model Object	Beware of DecimalFormat
Beware of floating point numbers	Include 'from', exclude 'to'
Passwords never in clear text	Fields should usually be private
Use @Override liberally	Avoid raw types
Avoid basic style errors	Use final liberally
Use a fake system clock	Tag or marker interfaces
Don't use tab characters	Structs are occasionally useful
Beware of Byte Order Marks	Wisdom, not rules
Nest classes with care	Prefer modern date classes
Short public methods	Hide .html and .jsp
Return Optional not null	Varargs for 1 to N
Uncommon classes need explicit imports	Beware of instanceof operator
Interface for constants	Use a testing framework (JUnit)
Output parameters	Do not break portability
String concatenation does not scale	Know the core libraries
Validate method arguments	Generating unique IDs
Naming conventions	Prefer empty items to null ones
Validate state with class invariants	Use javadoc liberally
Conventional name for return value	Conditional compile
Construct classes from the outside in	Consider immutable forms for dates
Use System.exit with care	Clarifying method
Self encapsulate fields

Servlets and JSPs

Refactor large Controllers	Use Model View Controller framework
Always maintain HttpSessions	Session scope objects often Serializable
Do not synchronize doGet, doPost	JSPs should contain only presentation logic
Beware of custom cookies	Repel invalid requests
Parse parameters into domain objects	Thread safety in web apps
Loss of data during restart	Prefer JSTL tags
Use templates to standardize layout	Pre populate forms
Prevent self linking	Send trouble ticket emails
Validate email addresses	Forward versus redirect
A Web App Framework WEB4J	Manage sessions closely
Struts seems mediocre	Choose form validation style carefully
Beware of doubly escaped ampersands	Use Cascading Style Sheets
Beware multilingual submit buttons	Prefer UTF 8 in all layers
Beware of common hacks	Understand details of FORM tags
Consider Controllers for redirects	Reuse login page for errors
Wrap file upload requests	Use extensions for fine grained security
Beware of URL rewriting	Serve binary content
Version links to CSS and JS	Sessions shared across tabs
Apply correct redirect code	Minimize site response time
Web usability guidelines	Emit flexible URLs
Escape special characters	Validate generated HTML
Measure web app performance

Common Tasks

Pattern match lines of a file	Representing money
Arrays as String	Logging messages
Send an email	Examine bytecode
Fetch text from the web	Determine if Strings are equal
Compare and sort Strings	Modernize old code
Read jar version information	Implement code tables
Command line operations	Open file in native directory
Run in debug mode	Memory stats
Define app name once	Copy an array
Measure application performance	Recovering resources
Generate random numbers	Internationalization
Replace a substring	Clipboard copy and paste
Get size of object in memory	Time execution speed
Parse text

Common Design Patterns

Type Safe Enumerations	Abstract Factory
Command objects	Template method
Model Objects	Factory methods
Plugin Factory	Wrapper (Decorator)
Immutable objects	Lazy initialization
Private constructor	Singleton

Functional Programming

Lambdas only for simple cases	Understand the functional style
Static import of Collectors	Annotate functional interfaces
Prefer standard functional interfaces	Beware forEach terminals

Swing

Look and Feel guidelines	Splash screen
Standardized dialogs	Verify input with regular expressions
Swing utility tasks	Swing threads
Preferences dialogs	Using preferences
Observers and listeners	Using JavaHelp
Change theme	Actions
Timers	Sort table rows
Filter table rows	Swing in general
Layout Managers	Input dialogs
Render table cells	Align menu items
A Swing App StocksMonitor	Don't subclass JDialog or JFrame
Provide an uncaught exception handler	Don't bury dialogs
Minimal Swing application	Verify input with Model Objects
Consider JGoodies Forms for layouts	Launch other applications

Databases

Keep SQL out of code	Don't perform basic SQL tasks in code
Consider data layer tools	Get database connection
Consider using standard SQL	Encapsulate connections
Simplify database operations	Use template for transactions
Business identifiers as String	Consider wrapper classes for optional data
Try pseudo persistence for mock ups	Data is king
Prefer PreparedStatement	Remember the basics of database design
Data access objects	Connection pools
Reduce database code duplication	Data exception wrapping

Tools

Using Ant for build scripts	Use Version Control tools
Using Tomcat for servlets	Using Maven for builds