Microsoft's Internet Explorer (IE) 4.0 has been out for a little over a week now, and the company now is shipping the 2.0 version of its Software Development Kit (SDK) for Java. According to Microsoft's Win32 Virtual Machine for Java Release Notes (see the Resources section below for links to this document and other information related to this article), the virtual machine (VM) for Java that ships with IE 4.0 is the same as the one in the new SDK. Using the Java class files that come with the SDK and comparing them to the Java class files that come with Sun's Java Development Kit (JDK) 1.1.4 release reveals exactly why Alan Baratz, president of Sun's JavaSoft division, said, "Microsoft deceptively altered key classes and inserted them into their SDK." (This was during the conference detailing Sun's October 7 announcement of Sun's suit against Microsoft alleging breach of contract. For more information on this lawsuit, see "Sun-Microsoft dispute gets ugly," in the October 1997 issue of JavaWorld.)
I have analyzed the classes and have run across seven areas that should be of great concern to developers if they want to develop solutions with Microsoft's SDK for Java that will work in other Java 1.1 certified environments. These areas of concern are:
- new classes (Hey, what's that class doing there?)
- new methods (And where did these methods and instance variables come from?)
- new variables (And where did these methods and instance variables come from?)
- modified interfaces (What about the interface changes?)
- the com.ms packages (Inside com.ms)
- missing methods (What's missing in the SDK)
- behavioral differences (And what's different)
These go far beyond the often-cited concern over Microsoft's lack of JNI and RMI support, as mentioned in my October 1997
Baratz used the word "deceptively" in Sun's announcement of the lawsuit because the (javadoc) documentation for the Java classes that comes with the SDK makes no mention of these changes. To find these differences, it is necessary to use either the ClassVue tool that comes with the SDK or manually examine the source code. Your best bet is to rely on ClassVue, as the source files provided with the SDK are not always the ones used for the generated classes. For those unfamiliar with ClassVue, the equivalent tool that comes with the JDK from Sun is javap, a class file internals examiner.
As much as I'd like to claim that what follows is an exhaustive list of changes to the SDK, it is possible that something was missed. With several items, there is a pattern -- so if you avoid similarly named things you should be okay. All of the problems identified here are in the java.lang, java.io, java.awt, java.util, and java.security packages/sub-packages.
So, what changed in each package?
- java.awt: New classes, New methods, New variables
- java.lang: New methods, New variables
- java.io: Dropped methods
- java.security: Modified interfaces
- java.util: New methods, New variables
The first set of changes in Microsoft's SDK for Java is new classes, methods, and variables that were added to the system packages. A system package, or core Java API, is anything that begins with java.* in its fully qualified class name. So, as far as new classes go, 16 new ones were added into java.awt. These are:
|Microsoft's new Java classes for AWT peers|
With the exception of the last one, all the classes are peer classes for AWT components, where a peer is the platform-specific representation of a graphical component like a button or menu. Normally, these classes would go into a different package like sun.awt.windows or sun.awt.motif. Since you aren't supposed to use them anyway, they should be easy to avoid. The
WUIPeer class also is a peer, but it supports a Microsoft-specific behavior. Stay away from that too. Additional package-private (also called friendly, for when no access specifier keyword is specified) classes were added, like
__UIMenuRoot. Because these are inaccessible outside of java.awt, you cannot directly use them.
The most commonly added method is called
getBaseName(). Thankfully, it too is package-private, although it should be just plain private. Other changes, like making
loadClassInternal() method private, instead of package private, are due to implementation differences and should have no effect on developers.
I don't mean to downplay the package-private changes that Microsoft made, but unless developers are extending the key Java class libraries themselves, they cannot access these changes. Since developers seeking cross-platform solutions know better than to inject their own changes into the key Java class libraries, this isn't an issue. (See Rule 3 of SunTest's "100% Pure Java Cookbook," referenced in the Resources section.)
The real problems appear with the public methods that Microsoft introduced:
|Public methods added into key Java libraries|
|java.awt.image.ColorModel||finalize() [was protected]|
Locale(String, String, String, int, int)
getLCID() [was private]
You will need to avoid all of the above methods, unless you want your Java programs to run only with Microsoft's environment. In addition to these new methods, you have access to three new instance variables and lots of new Locales for internationalization:
|Instance variables incorporated into Java API|
PUBLIC_DECLARED is brand new to
appWorkspace is brand new to
pData was private and is now public. As with everything else, avoid them. As far as the Locale objects go, Microsoft's environment seems to understand a few additional languages, that JavaSoft doesn't. While the intention is good, instead of using the new constants, you should create a Locale object yourself, with the necessary parameters, although not using the new Locales may require some extra work when formatting messages.
For each Locale added, there are two public classes added into the java.text.resource package. Because Sun's documentation specifically states that you should not directly call any API in text.resource, I do not view these additions as a problem.
An interface defines a partial template that a class must follow. Microsoft seems to have modified the templates of some of the security interfaces:
|Additional methods in Java security interfaces|
The way interfaces work, when you create a class that implements an interface, you define a method for each method declared in the interface. By increasing the number of methods in the interfaces, Microsoft is breaking every class that implements each original interface. If you need to create programs to work in both Microsoft and non-Microsoft environments, it is necessary to always implement the additional behavior, whenever you implement either interface in a class.
com.ms is a grouping of classes delivered with Microsoft's proposed Java implementation. All the classes within com.ms.* packages normally are inaccessible to people using Netscape Navigator/Communicator and Java 1.1 environments. If you choose to use something from a class in a com.ms.* package, more than likely you are moving outside the realm of portability. One example in which this may prove tricky for the uninformed is getting
FontMetrics from the
Toolkit class (via
getFontMetrics()). While the method signature is the same "
public FontMetrics getFontMetrics()," what you get back is an instance of
com.ms.awt.FontMetricsX. If you treat it as a
FontMetricsX object, your program will work only with the Microsoft virtual machine for Java; if you stick with
FontMetrics, then you're portable.
There is an exception to this com.ms avoidance rule though: Microsoft's Application Foundation Classes (AFC) in com.ms.ui (see Resources) are written in Java. So you can use them. However, if your users are not using IE 4.0, you will need to provide them separately.
(Until Microsoft bundles the AFC classes into something that is usable in a non-MS Java environment, providing AFC separately isn't an option as the AFC classes included with IE4 and their SDK rely on Microsoft Java VM specifics. There should soon be a bundling of the AFC classes usable in other browsers like Netscape Navigator 3.0. Watch Microsoft's website for details.)
Out of all the classes I searched, the only thing missing from Microsoft's proposed implementation of Java 1.1 is one method. Now, one missing method is still one too many, but the fact is, the missing method is relatively minor. Specifically, the
toString() method of
ByteArrayOutputStream that accepts a character encoding name as a parameter isn't present. A character encoding permits localized display of text messages. The workaround for this omission is to ask for the byte array of the stream (
toByteArray()) and then use the
String constructor that accepts an encoding name. By always taking these two steps, even with the JDK, you'll be sure your programs will work when used with Microsoft's runtime environment.
The last bunch of changes I'll be discussing here actually has nothing to do with new classes or missing methods. It has to do instead with behavior differences. Whenever a new environment comes out, you need to learn how it behaves differently from what you expect. As an example, when Netscape Navigator 3.0 beta 5 came out, the browser reported additional AWT events to programs. If your programs weren't ready for these additions, the programs didn't behave appropriately. Now, with the new SDK, it appears that kind of upheaval is once again upon us.
First and foremost, Microsoft's Win32 virtual machine for Java reports itself as Java 1.1 (notice no point anything after the second one in "1.1"). Currently, Sun is shipping the Java 1.1.4 release of the JDK. That means your favorite bug fix may not be included in the Microsoft JVM. Now, it is possible the bug fix isn't necessary because of implementation differences or it's possible that Microsoft corrected the problem on its own. However, if you glance through the source and do comparisons, you will notice obvious functional differences. If you expect the JDK behavior and don't get it, your program still needs to function appropriately.
For example, when using
java.awt.BorderLayout, if you add a component with no quadrant name, it goes in the center quadrant when run with the JDK or Java Runtime Environment (JRE). If you add a component with an illegal quadrant name, like "Top,"
BorderLayout throws an
IllegalArgumentException. On the other hand, try the same program with no quadrant name on Microsoft's environment, and the component is not displayed anywhere. (This affects the Swing JFrame component, making it unusable.) Another difference is that the
Dialog class will accept a null parent
Frame parameter for Microsoft, while the Sun JDK throws an
IllegalArgumentException. As people run more programs under IE 4.0, more of these differences will emerge.