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Frustrated with your Java project? 
We have the resources to help

If you have a question about Java programming that you need answered - you're not alone. You may even be asking yourself some of the same questions that have confused and baffled other Java programmers. Here are a selection of common questions and their answers (sorted by date, so most recent is at the bottom of the page). 

Questions

Questions have been grouped into categories, for easy searching. If you still can't find it, check the miscellaneous section, or email me the question.

Applets

• How do I debug my Java applets to see what's going
  wrong?

• How can I change the gray background of an applet?

• How can I load a particular HTML page from within an applet?

• What is the difference between an applet and an application?

• Why can't my applet read or write to files?

AWT / Graphics

• How do I gray out components, and prevent users from using them?

• How can I create my own GUI components?

• How can I find out the current screen resolution?

• How do I create a modal dialog box?

• How do I create a scrollable container?

• How can I change the cursor shape?

• How do I make my frames close in response to user requests?

• How do I minimize and restore frames and JFrames?

• How do I playback multimedia files? I'd like to display .avi, .mpg, and other movie formats.

• My application/applet loads images, but they aren't drawn to the screen. What's going on?

I/O & Files

• How can I append an existing file in Java?

• How can I read from, and write to, files in Java?

• How do I connect a Reader class to an InputStream?

• Why can't my applet read or write to files?

• When should I use an InputStream, and when should I use a Reader?

• How can I provide a directory listing, and allow the user to navigate directories and select a file?

• How can I write primitive data-types to disk? In C/C++, the printf statement could write integers, floats, as well as other types.

Language questions

• When converting older Java software written for JDK1.0 to run on a newer JVM, are there any issues I should be aware of? Are all future versions of Java guaranteed to be backwards compatible?

• How do I pass a primitive data type by reference? For example, how do I make an int passed to a function modifiable.

• How I can find the class of an object?

• How can I create an event handling mechanism in Java?

• With Microsoft not supporting Java anymore, what should I do?

• How I can I return a null value from an object
  constructor?

• What does a void return value mean? Which class is
  being returned?

• How do I compare two strings?

• How do I create a new instance of an object?

• What are exceptions, and when should I use them?

• How can I throw an exception without declaring it in a 'throws' clause?

• When I compile a Java application using the new JDK1.1 compiler from Sun, it says that it uses "a deprecated API". What does this mean?

• What's the difference between a member variable, and a local variable?

• I've heard that Java has automatic garbage collection. How does it know when I'm finished with data, and to free some memory space?

• What is an abstract class, and when should it be used?

• What is Pure Java? I've heard that its 100% Java, so if I only use Java code and no external applications, is my code 'pure'?

• How do I kill a thread? The stop() method is deprecated
  in JDK1.2, so how do I shut it down?

Data type issues

• How do I convert between an int and a char?

• How do I convert from a char to an int?

• How do I convert between a String and a number?

• How do I get the length of a string?

Keywords

• What does the keyword 'static' mean?

• What is the difference between public, private, and protected keywords? Do I even need to use them?

• What does the 'extends' keyword mean?

Operators

• What's the difference between = & == ?

• What does the ++ or -- signs after a variable mean?

Networking

• How can I read the status code of a HTTP request?

• How can I find out who is connected to my server?

• What exactly are servlets?

• How do I get parameters from a HTML form when using servlets?

• How do I send cookies from a servlet?

• How do I read browser cookies from a servlet?

• How do I make cookies expire after a set time period?

• How can I poll a remote server, to see if it is still available?

Java.util package

• How do I use the Vector class, from the java.util package?

• What's the use of a StringBuffer?

• How do I use hashtables?

• How do I use stacks in Java?

Miscellaneous

• How do I run the garbage collector to free memory
  and delete unused objects?
  
• Mirror of the Java Signing FAQ - learn how to digitally sign applets
  
• What is a magic number?
  
• I can't compile .java files. Help me please!
  

• Why did Java skip from Version 1.1 to Version 2?

• What are the Java Certification exams?

• What is a Sun Certified Java Architect?

• How can I use a quote " character within a string " ?

• What exactly are Java Beans?

• How can I tell the type of machine and OS my Java program is running on?

• How can I generate random numbers?

• What causes out of memory exceptions?

• How do I create a .JAR file?

• How do I execute other applications?

• How do I use really large numbers in Java?

• Is there any way to access C++ objects, and use their methods?

• Is Java Y2K compliant? Where can I find more information?

• How do I detect if command line arguments are empty?

• My version of JDK won't run classes, even when they're in the current directory. What should I set my classpath to?

• How can I convert my Java classes to an executable .EXE file for Windows?

• Who created Java?