6.825: Java Resources

• Java Documentation (all versions)
• Java Tutorial is a great place to start if you are new to Java.
• The Java Programmer's FAQ is a great resource with lots of practical information. (This link seems to be broken temporarily?)
• IAQ: Infrequently Answered Questions on Java, written by Peter Norvig

Several people have asked which books are best for learning Java. The answer depends on prior programming experience and personal inclination.

Professor Kaelbling recommends the following two books:

• Understanding Object-Oriented Programming With Java by Timothy Budd
• The Java Programming Language by Ken Arnold, James Gosling, and David Holmes

Mike Ross recommends Java In A Nutshell by David Flanagan (online here if you are on an MIT network), but admits that it is only helpful if you are already familiar with object-oriented programming from C++. In addition, the newest edition splits all the information about AWT and Swing (the graphics display classes) into a separate book, Java Foundation Classes In A Nutshell.

Juan Velasquez recommends Thinking In Java by Bruce Eckel, which is also available at Amazon.com and at Quantum Books.

Also, MIT has a subscription to Safari which allows you to look at many technical books online. It's available through Vera on the MIT libraries page.

Free Tools

If you shudder at the thought of developing in Emacs or Vi, there are several free Java IDEs that you can check out. Netbeans and Borland's JBuilder Personal will work on Solaris, Linux, or Windows, and Netbeans also supports Mac OS X. For the purpose of class assignments, however, Emacs, Vi, Notepad, or some other text editor will be perfectly adequate.

Debugger

Java comes with a command-line debugger, jdb, which is not very full-featured. IDEs usually come with integrated graphical debuggers. If you want to use a debugger, but don't want to use an IDE, try JSwat.

Beanshell

Even if you are an experienced Java programmer, you may not have heard of Beanshell. Beanshell provides an interactive text-shell environment for evaluating Java expressions and interacting with a running JVM. This is a very useful debugging tool, as it allows you to instatiate and call methods on objects without recompiling (though you do need to restart the shell if you want to change a compiled class).

You should avoid using the 1.3 releases of Beanshell, they have serious bugs in managing for-loop iterations. Use the 1.2 releases instead. The 2.0 releases are brand-new betas and may also be buggy (although they do not have the aforementioned for-loop bug).

To install beanshell,

1. Download the JAR file
2. Add it to your classpath, by:
   • Placing it in the lib/ext directory of your JVM, or
   • Placing it in ~/Library/Java/Extensions on MacOS X, or
   • Adding it to your UNIX/Windows environment variable
3. Run it by:
   • Double-clicking the jarfile (MacOS X, Windows + Sun JDK), or
   • Typing "java bsh.Interpreter" from the command-line, or
   • Typing "java bsh.Console" to run a GUI version

More documentation is available on the Beanshell website.

Assorted Tips

• If you are a C++ programmer with little or no Java experience, do not make the mistake of thinking that "Java is C++ without pointers," or "Java is C++ with everything as a class," etc. Many of these simplifications are wrong and will lead you astray. The first statement, "Java is C++ without pointers," is especially hazardous to your health. In Java, unlike C++, all objects and arrays are created on the heap and are not in the stack. The stack only contains primitive types and references to objects. When you declare Bozo x = new Bozo();, you are creating an object on the heap and declaring that x is a reference to it. When you pass x around, assigning it to different variables and passing it to functions, it is passed by value. So if I say Bozo y = x;, y refers to the same Bozo as x does. But the following method has no effect:
  public void swap(Bozo x, Bozo y) { Bozo temp; temp = x; x = y; y = temp; }
  
• If you want to copy arrays quickly, use System.arraycopy().
   
• ArrayLists can save a lot of the bookkeeping hassle required to use arrays correctly, and they are very efficient.
   
• The Java data structure classes (ArrayLists, HashMaps, Sets, etc.) are often referred to as the "Collections" and are all in the java.util package.
   
• Some Java classes support the clone() method, but you must be careful before using it. A clone() usually creates a shallow copy of an object. So, if you clone() a Vector, you get two different Vectors with independent internal data structures (i.e. you can delete elements from one Vector and they will remain in the other Vector), but the objects the Vectors contain are not duplicated - they both refer (at least initially) to the same set of objects.
   
• Be careful about correctly overriding methods from java.lang.Object, including clone, toString, equals, hashCode, and finalize. See this excellent essay by Mark Roulo for details.