What’s Java?

♦4. Types of Java

	Let's talk about Java in greater detail. Java can be broadly classified into three types, each for a different purpose. Take a look at the next table. Programmers choose different types of Java depending on how their programs will be used.
	I get it! So I should use J2ME because I'm making mobile phone apps, right?
	That's right, my boy. J2ME is Java for applications in electronics and appliances, PDAs, mobile phones, and similar devices.

Types of Java

Name	Purpose
J2EE(Java2 Enterprise Edition)	For core systems and enterprise applications
J2SE(Java2 Standard Edition)	For desktop computers and other standard computer applications
J2ME(Java2 Micro Edition)	For electronics and mobile phone applications

♦5. Mobile Java

	Nikki, you use your handset a lot, don't you? What's your impression about it?
	Yeah, I do. When people think of mobile phones, they think about calling and emailing. After I started using mine, though, I was surprised to find out I could surf the Web and play games with mobile apps.
	I can imagine. Times have changed. Handsets aren't limited to just calling anymore. They have evolved to let us email, browse webpages, and use mobile apps.
	I was really surprised to discover I could play games on my phone, just like on a computer or game system.
	When mobile apps became available, it really opened the door for us. Now we can enjoy animation, sound, data storage, and other features that handsets only equipped for calling, email, and Internet access don't offer. And once you download a mobile app, there's the advantage of not needing to go online again to use it.

	Well, I think we're finally ready to talk about Java for developing mobile apps. J2ME supports many, many more devices than J2SE or J2EE. These devices come in many shapes and sizes, with processing and memory capacities and interfaces that vary greatly from device to device. That's why there's no single, standard development kit (SDK) for J2ME like there is for J2SE and J2EE. So to support all these different devices, J2ME defines configurations and profiles instead.
	Hmm. . . . Seems a little tricky.
	Maybe. But once you get the idea, my boy, it's easy. Configurations are narrowed-down sets of J2SE functions that support devices with limited processing power. These configurations define the core features of J2ME. A lot of different devices are supported with J2ME, and they all have their own special features— vibration for mobile phones, pen input for PDAs, and so on. How does J2ME handle these device-specific features? Through profiles. So you see, J2ME supports many kinds of devices through combinations of configurations and profiles.
	I don't get it.
	You might say that the configuration is the basic part and the profile is the specialized part.

One configuration is called the Connected Device Configuration, or CDC, and another is the Connected Limited Device Configuration, or CLDC. CDC supports car navigation systems and other devices with mid-range processing power. CLDC supports mobile phones, PDAs, and other devices with processing and memory limitations. And depending on the configuration, you'll use a different Virtual Machine (VM). CDC uses the Java VM (JVM), just like J2SE. But CLDC uses the K Virtual Machine (KVM), which requires less memory and processing power.

	Next I'll tell you about the profiles. CDC has what is called the Foundation profile. Meanwhile, CLDC for mobile phones and similar devices has profiles including MIDP and DoJa. The supported profiles vary depending on the mobile phone manufacturer or the telecom carrier, so we must be sure to use compatible ones.
	My mobile phone is an NEC N820, so what's the supported profile?
	MIDP is the profile supported by your N820 handset. MIDP was created by Sun Microsystems, the developer of Java, as a profile for mobile phones. It's now the most popular profile worldwide. I'm going to teach you how to develop MIDP mobile apps in these lessons. By the way, you may have heard of DoJa. It's a specialized profile designed by the Japanese mobile service provider DoCoMo.

♦6. Looking ahead

	Did our talk give you an idea of what mobile Java is, Nikki?
	Yeah, I think I get it, mostly. But it seems difficult. I wonder if I can really do it. . . .
	You can do it, my boy! Everyone's a little uneasy at first, learning new things. Next time we'll put together your development environment for creating apps. After you install the tools you need on your computer, you can try your hand at running a program.