This article introduces some of the Java features in Leopard. With improvements including better performance, 64-bit computing, new options for choosing the version of Java you want to run, and new tools to better analyse your Java code, Leopard reflects Apple's focus on providing the best possible Java experience on Mac OS X and supporting the latest hardware, while preserving compatibility.

Take Advantage of Intel 64-bit Computing

Mac OS X Leopard breaks the barriers of 32-bit computing and allows you to run next generation 64-bit applications side-by-side with current 32-bit software in the same operating system. On Macs with Intel Core 2 Duo or Xeon processors, this support is extended to Java applications.

For traditional desktop applications like word processors and spreadsheets, the 32-bit address space that has been used for the last few decades is enough. For the next generation of data intensive applications, such as those that work with the human genome or geospatial data, the 4GB of memory space that 32-bit addressing allows suddenly becomes very limiting. Sixty-four-bit computing shatters the 4GB limit allowing applications to address more than 16 exabytes of memory space.

To put the difference between 32-bit and 64-bit computing into perspective, imagine that you are working with a dataset in which the road area of the Golden Gate bridge can be represented in a 32-bit address space. With 64 bits of address space, you have the ability to model the entire surface of the Earth at the same resolution.

There are several ways to run your Java application in 64-bit mode. On the command line, you can use the -d64 flag. For example, you can set a launch script to execute the following:

/System/Library/Frameworks/JavaVM.framework/Versions/1.5/Commands/java -d64 MyApp

For double-clickable bundled applications, you can request that the 64-bit virtual machine be used by adding the following to your application's Info.plist file:

<key>JVMArchs</key>
<array>
  <string>x86_64</string>
</array> 

If the 64-bit virtual machine isn't available, the default 32-bit version will be used.

For pure Java applications running on 64-bit capable Intel hardware, either of the above steps is all you need to run your Java application in 64-bit mode. If you have native code in your application, however, you need to create a universal library that contains an x86_64 executable as well as PPC and i386 variants.

Once you have your application running in 64-bit mode, you'll probably want to increase the heap size. On the command line, you need to use the -Xms and -Xmx arguments to define the initial and maximum heap sizes. For a bundled application, you'll need to add the following to your Info.plist file:

<key>VMOptions.x86_64</key>
<string>-Xms2g -Xmx8g</string>

An important thing to note is that when running with large heaps of memory, it can take longer for the virtual machine's garbage collector to operate. You may want to experiment with alternative garbage collectors, such as the Concurrent Mark and Sweep collector, enabled with the -XX:+UseConcMarkSweepGC runtime flag, or the Parallel collector, enabled with the -XX:+UseParallelGC runtime flag.

Run Multiple Versions of Java

Mac OS X includes multiple versions of Java, and lets you run them side by side. The Java Preferences Application, located in the /Applications/Utilities/Java folder, lets you set the version of Java that is used by default on the command line as well as for applets, package applications, and Java Web Start applications. If you want to use a version of the JDK that's not the default, you can directly execute the version you want to use on the command line.

To make it easy to use multiple versions of Java on the command line, here's a tip. Add the following two lines to your ~/.bash_profile file:

alias java15=/System/Library/Frameworks/JavaVM.framework/Versions/1.5/Commands/java
alias java14=/System/Library/Frameworks/JavaVM.framework/Versions/1.4/Commands/java

Now, when you open a new shell, you're set to go. For example:

$ java14 -version
java version "1.4.2_16"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.4.2_16-b05-302)
Java HotSpot(TM) Client VM (build 1.4.2-85, mixed mode)

$ java15 -version
java version "1.5.0_13"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_13-b05-237)
Java HotSpot(TM) Client VM (build 1.5.0_13-119, mixed mode, sharing)

You can take this tip one step further and add the ability to run your applications with a 64-bit address space. For example, you could define the following alias in your ~/.bash_profile file:

alias java64="java15 -d64"

Then, when you open a new shell, you'll be able to do the following:

$ java64 -version
java version "1.5.0_13"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_13-b05-237)
Java HotSpot(TM) 64-Bit Server VM (build 1.5.0_13-119, mixed mode)

Developer Tools Support

Instruments, introduced in Leopard, helps developers better understand how their applications run. It lets you visualize multiple aspects of system and application performance over time, including CPU load, network activity, graphics activity, user events, and memory allocations. For the Java developer, Instruments provides built-in support for inspecting Java applications as they run, including monitoring activity on every thread.

In addition to ground-breaking performance and analysis tools, Leopard includes several Java-community developed tools, including Ant and Maven. By including these command-line tools, you can more easily get right to work on your Java software with a minimum of setup. You can download any open source Java project and have everything you need to get right down to business.

As well, Xcode's new Organizer features drag-and-drop support for Ant-based projects. You can either open up a directory containing your codebase, or create a fresh Ant-based project right from the Organizer. After that, building your project is as simple as pushing the Build button.

Run Faster

Leopard includes the best community-developed tools, such as Ant and Maven, support for 64-bit applications to Java, and unprecedented visibility into the inner workings of your applications. Yet another important feature is the enhanced performance of the Java runtime on Leopard. Java applications will see an average of 10% improvement in performance on Leopard compared to Mac OS X Tiger. These performance increases are due to work done both in the Java virtual machine and in the operating system as a whole.

Also, Java applications that take advantage of 64-bit support can see even greater improvements in performance, thanks to being able to take better advantage of the increased registers and other features of the Intel Core 2 Duo and Xeon processors that aren't available to 32-bit applications.

Posted: 2007-12-04