A Thread is runnable, how does that work?

Learn Java programming

• Is there a tool to type Java code and see what happens? (stub article)

Java jargon

• What is the difference between the JVM, JRE and JDK? (stub article)

Java operators and arithmetic

• How do I add two numbers in Java? (stub article)
• How should I round a double up to an int? (stub article)
• How can I calculate minimum, maximum and average using Java? (stub article)
• What are bitwise and bit shift operators? (stub article)

Variable scope

• Why does this for loop instantiation fail to compile? (stub article)

Class relationships and references

• How do I access a variable declared in another class? (stub article)

Java design patterns

• What is a recursive method? (stub article)
• What is a singleton? (stub article)
• How do I format my price correctly? (stub article)
• What is a factory method? (stub article)
• How should I create an immutable class? (stub article)
• What are adapters in Java? (stub article)

Java application development

• How can I sort 3 numbers using Java? (stub article)
• How can I make spelling checker with a LinkedList dictionary? (stub article)
• How can I use SAX to parse a Web page via JTidy? (stub article)

Interface concepts

• What is the difference between abstract classes and interfaces? (stub article)

Interface use

• When should I use abstract classes rather than interfaces? (stub article)
• What are the rules for passing subclasses for method arguments? (stub article)
• Can you give an example of multiple inheritance with interfaces? (stub article)

How to define an interface

• Should I use a public access modifier for interface methods? (stub article)
• Can we create a Java class inside an interface? (stub article)

How to implement an interface

• Can you show how to implement an interface? (stub article)
• This code seems to be instantiating an interface! (stub article)
• When interfaces clash, which method answers the call? (stub article)

Marker interfaces

• Can you show an example marker interface? (stub article)

Interface constants

• This interface variable is assigned in a constructor! (stub article)

Concurrent programming features

• What is a thread? (stub article)

Threads and runnable types

• How does the run() method in Runnable work? (stub article)

Thread management methods

• Which class is the wait() method defined in? (stub article)
• Why are there separate wait() and sleep() methods? (stub article)

Multi-threaded design questions

• Do I need to use synchronized on setValue(int)? (stub article)
• How do I create a Runnable with inheritance? (stub article)
• Which has priority with a static synchronized thread? (stub article)

Java inheritance principles

• Is inheritance applicable for beginners in programming? (stub article)
• Can you show examples of Java inheritance? (stub article)
• How does inheritance avoid duplication? (stub article)

Multiple inheritance

• Why doesn't Java support multiple inheritance? (stub article)
• Is multiple interface inheritance better than extending a class? (stub article)

Extending classes

• What's the difference between importing and extending a class? (stub article)

Overridden methods

• Can you give an example application that shows overriding? (stub article)
• How can I find the inherited attributes of a class? (stub article)

Techniques for overridden superclasses

• Can you give an example call to an overridden superclass method? (stub article)
• How can I get the superclass to call back to a method in the subclass? (stub article)

Abstract class design and use

• Why use an abstract class instead of an interface? (stub article)
• What's the use of concrete methods in abstract classes? (stub article)

Abstract method design constraints

• Can you show some static calls to abstract classes? (stub article)

Abstract classes and methods

• How can I call a concrete instance method on an abstract class? (stub article)
• Can you give an example of an abstract class? (stub article)

The static main method

• How can I write a program that takes command line input? (stub article)
• What does public static void main(String[]) mean? (stub article)

Overloading the main method

• Can you give an example of overloading the main()? (stub article)

Main method arguments

• Why does the main() method take a String array argument? (stub article)
• How can I print the main method arguments in reverse order? (stub article)

Calling the main() method

• How many arguments can be passed on the command line? (stub article)
• How can I make an interactive command line interface? (stub article)

Language features

• Is Java a fully object oriented language? (stub article)
• What are keywords and reserved words? (stub article)
• How can I develop in my local language in Java? (stub article)

Java data types

• What Java types are available? (stub article)
• What's the difference between primitive types and arrays? (stub article)

Java language design concepts

• What's the difference between abstraction and encapsulation? (stub article)
• Is println() overloading or overriding? (stub article)
• What is dynamic method dispatch? (stub article)

Understanding constructors

• What is a constructor? (stub article)
• How do I invoke a constructor? (stub article)
• How can I call a constructor from a constructor? (stub article)
• Is it OK to tag inline method calls on constructors? (stub article)

Object design

• How can I count the number of instances of an object? (stub article)
• Can objects be used in place of arrays? (stub article)
• What's the difference between equals and ==? (stub article)

Object methods

• How does an object call an inner class method? (stub article)

Object comparison methods

• When is hashCode() used? (stub article)
• How can I create a constructor to equate two other objects? (stub article)

Static variables

• What is special about static variables? (stub article)
• I get "non-static variable this cannot be referenced from a static context"! (stub article)

The static modifier

• What is the difference between static and final keywords? (stub article)

The String class

• Why is the String class declared final? (stub article)
• How many objects are created for identical strings? (stub article)

String methods and operators

• The == operator doesn't match strings correctly! (stub article)
• How can you say the + operator is not overloaded in Java! (stub article)
• How can I reverse the characters in a string? (stub article)

String buffers and tokenizers

• Why don't two StringBuffers match? (stub article)
• How can I pad a StringBuffer? (stub article)
• What is a StringTokenizer for? (stub article)
• How can I get a person's initials from their full name? (stub article)

Regular expressions

• How can I check a string has no numbers? (stub article)

Java system integration

• How do I get the name of the operating system? (stub article)
• How do I find the size of an object in Java? (stub article)
• How can I copy process information from Windows task manager? (stub article)

Java exceptions

• What's the difference between checked and un-checked exceptions? (stub article)
• What is a NullPointerException in Java? (stub article)
• What's the best way to handle a NullPointerException? (stub article)
• Can you give an example of catching an exception? (stub article)
• How can I throw a NumberFormatException back to the main() method? (stub article)

Class loading

• How can I get a class reference without using new operator? (stub article)
• What's the difference between the Class.forName() method and the new operator? (stub article)
• How can I implement the Class.forName() scheme? (stub article)
• How can I cast an unknown sub-class returned by newInstance()? (stub article)
• Is Class.forName() runtime polymorphism? (stub article)

Java Abstract Window Toolkit classes

• How do I draw a Rectangle on a Graphics instance? (stub article)
• What is the difference between heavyweight and lightweight components? (stub article)

Getting started with JDBC

• How does Class.forName(dbDriver) work with DriverManager.getConnection()? (stub article)
• How do I use JDBC with Microsoft SQLServer? (stub article)

Java SQL API

• What's the difference between Statement and PreparedStatement? (stub article)
• How can I insert multiple records at a time? (stub article)
• Why it is better to use PreparedStatement? (stub article)

JDBC techniques

• How do you make a database insert using JDBC? (stub article)
• How can I use system variables to make a database connection? (stub article)

JDBC problems

• I get "cannot find symbol" for my executeUpdate(String) call! (stub article)

SQL queries

• How can I select records between two dates? (stub article)
• What is a database view? (stub article)

Storage structures

• What is the difference between Hashtable and HashMap? (stub article)

Working with dates and calendars

• How do I insert slashes in a date? (stub article)
• How can I convert a String into a Date object? (stub article)
• How can I get the difference between two dates in days? (stub article)
• Why isn't my custom Calendar class called? (stub article)

Compiler concepts

• Which class should be compiled first? (stub article)

Compiler commands

• What are the steps in compiling a class? (stub article)
• What do I type at the command line to compile Hello.java? (stub article)
• Where is my compiled class file? (stub article)
• How can I compile Java classes with packages on the command line? (stub article)
• How can I ensure my compiler will locate the SAX package? (stub article)

Compiler diagnostics

• What does this deprecation message mean? (stub article)
• What are undefined and undeclared variables? (stub article)

Development environment

• How do I set the compiler path? (stub article)
• How do I set environment variables on Windows XP? (stub article)
• How do I configure EditPlus to compile Java and capture output? (stub article)

Read and write files

• How can I divert console output to a file? (stub article)
• How can I generate an array from a list? (stub article)

File system navigation

• How can I get the full path of Explorer.exe? (stub article)
• How can I get the path to an installed program? (stub article)
• How do I limit the scope of a file chooser? (stub article)

Input and output streams

• Is it best to customise state with Serializable or Externalizable? (stub article)

Java visibility modifiers

• Can constructors have visibility modifiers? (stub article)

Java Web clients

• How can I download a Web page and write it to a file? (stub article)
• My Java Web client gets the wrong site! (stub article)
• How can I set a code name identifier for my feed reader? (stub article)

Java networking API

• How do I get the registered domain name from a URL? (stub article)
• How do I get a domain name from an IP address? (stub article)

Servlet programming

• Can I use a normal class to handle my requests? (stub article)
• Can I use a constructor in my servlet? (stub article)

Servlet start up

• How do I compile a servlet? (stub article)
• Why won't my servlet compile? (stub article)
• What is the difference between JAR and WAR files? (stub article)

Servlet techniques

• What is URL-rewriting? (stub article)
• What's the difference between forward, include and redirection? (stub article)

General container questions

• Is the session ID stored in the servlet or container? (stub article)

Web application configuration

• What is a servlet URL mapping? (stub article)
• How do I load a servlet at start-up? (stub article)