1.5 Working with Eclipse


You use the Eclipse Java Development Tools (JDT), a series of six seamlessly integrated plug-ins, for Java development in Eclipse. Even if you've written Java for years , you're about to have a whole new experience, one that makes Java development so smooth that when you understand how to use the JDT, you'll wonder what took people so long to make this a reality.

Eclipse is all about code development, and the only way to really understand what's going on is by creating code, so we're going to start by using the JDT to create and run the amazingly useful application you see in Example 1-1. This Java application just displays the message "No worries." on the console.

Example 1-1. The Ch01_01.java example
 public class Ch01_01 {     public static void main(String[] args)     {         System.out.println("No worries.");     } } 

How can you create this application using Eclipse, and how is Eclipse going to make your job easier? The answers are coming up right now. In Eclipse, all Java code must be inside a Java project, so the first step is to create a Java project.

1.5.1 Creating a Java Project

To invoke the Java perspective, and enter the code for our first example, Ch01_01.java , start Eclipse and select the Window Open Perspective Java menu item to open the Java perspective using the JDT, as you see in Figure 1-6. This is the perspective you'll use over and over as you start relying on Eclipse for Java development.

Figure 1-6. The Eclipse Java perspective

It's worth getting to know the Java perspective before we start using it. At the top are the standard menu bars and toolbars , populated with new items for the Java perspective, which we'll become familiar with in the coming pages.

The left pane holds the Package Explorer and Hierarchy views, and you use the tabs at the bottom of this pane to flip between these views. The Package Explorer view gives you an overview of the package you're working on and lets you navigate through Java projects, selecting what files you want to open in the editor. The Hierarchy view lets you examine type hierarchiesyou select an item in a code editor, right-click it, and select the Open Type Hierarchy context menu item. When you do, the hierarchy view will display the hierarchy of that item, giving you a clickable inheritance tree for the item, including all members . That can be a big help if you're trying to figure out the syntax of methods you want to override or which methods are available.

The Outline view in the pane at right presents a structured, hierarchical view of the contents of the file open in the main editor pane and lets you jump to elements in it. This is great for developers who are accustomed to using a simple text editor to develop long Java files, because this view organizes the main sections of long code files, letting you move around at will (more on this view in the next chapter).

At the bottom of the Java perspective are the Tasks and Console views, which you can select between using tabs. The Tasks view displays pending tasks , such as errors that the compiler has noticed and which need to be fixed, and the Console view shows you what's going on in the output consoleour sample application will write to the Console view, for example.

Editors are stacked in the middle pane and are accessible with the tabs at upper left in that pane. The JDT code editors give you an immense amount of power, far beyond simply entering text. There are all kinds of hidden assets built-in here, most of which are utterly unobtrusive until you decide you want to use them.

That gives us an overview; to create a new Java project in the Java perspective, select the File New Project menu item now (alternately, right-click the Package Explorer and select the New Project context menu item), opening the New Project dialog box, as you see in Figure 1-7.

Figure 1-7. The New Project dialog box, first pane

Select the Java and Java Project items and click Next to bring up the next pane of this dialog box. Enter the name of this new project, Ch01_01 , in the Project Name box, and click Next, bringing up the next pane of the dialog, which you see in Figure 1-8. As you can see in this pane, we're about to create a new project named Ch01_01 in its own folder. You can use the Projects tab here to include other projects in the build path, something we'll do as our projects become more involved. The Libraries tab lets you browse to libraries and JAR files you want included in the build path; by default, only the JRE System Library is included. The Order and Export tab lets you specify the order of classes in your build path , and gives you the option of whether you want to export the current projects so its code will be available to other projects. In this case, just click Finish to create our new project, Ch01_01 .

Figure 1-8. The New Project dialog box, third pane

This adds the new Ch01_01 project to the Package Explorer, as you see in Figure 1-9. The project is represented as a folder in your workspace, and, at this point, the folder only contains the libraries we've included on the build path, the JRE System Library.

Figure 1-9. A new project in the Package Explorer

Projects like this organize your files, classes, libraries, and exports. We don't even have any code in this one yet, so the next step is to add a new public Java class to the project.

1.5.2 Creating a Java Class

In our example, the public class is Ch01_01 , and Eclipse stores public classes like this one in their own files. There are several techniques for creating new classes in Eclipse: you can use the toolbar item with the circled C icon, you can use the File New Class menu item, or you can right-click a project in the Package Explorer and select the New Class item in the context menu. Any one of these methods opens the New Java Class dialog box you see in Figure 1-10.

Figure 1-10. Creating a new Java class

Note the options in this dialog. You can set a class's access specifier public , private , or protected ; you can make the class abstract or final ; you can specify the new class's superclass ( java.lang.Object is the default); and you can specify which, if any, interfaces it implements. We're going to put our examples into Java packages to avoid any conflict with other code; here, we'll use packages named after the example's chapter, like org.eclipsebook.ch01 . In this case, just enter the name of this new class, Ch01_01 , in the Name box, and enter the name of a new package we'll create for this class, org.eclipsebook.ch01 , in the Package box, and click Finish to accept the other defaults. Note, in particular, that under the question "Which method stubs would you like to create?" we're leaving the checkbox marked "public static void main(String[] args)" checked. Doing so means that Eclipse will automatically create an empty main method for us.

Clicking the Finish button creates and opens our new public class, Ch01_01 , as you see in Figure 1-11; note the package statement that creates the org.eclipsebook.ch01 package. This new class will be stored in its own file, Ch01_01.java , in the Eclipse folder workspace\Ch01_01 .

Figure 1-11. A new Java class in Eclipse

So far, so good; you can see the main method that Eclipse has added to our class already. Now let's enter some code of our own.

1.5.3 Using Code Assist

You can type in code using the JDT's editor as with any editor, as you'd expect, but there's a lot more utility here than in a standard text editor. For example, the JDT also supports a facility named code assist that helps you by completing code you've already started to type, and it's a handy tool you'll find yourself using over and over.

For example, say that you want to enter the code System.out.println("No worries."); in the main method. To see code assist do its thing, move the mouse cursor inside the main method's body and type System ., and then pause. Code assist will automatically display the various classes in the System namespace, as you see in Figure 1-12.

Figure 1-12. Using code assist to create a method call

When you highlight out in the list of possible classes with the mouse, code assist will give you a rundown of what this class does, as you see at left in the figure. Double-click out in the code assist list so that code assist will insert it into your code, and type a period to give you System.out ., and pause again. Code assist will display the methods of the out class. Double-click the code assist suggestion println(String arg0) , and code assist will insert this code into the main method:

 public class Ch01_01 {     public static void main(String[] args)     {  System.out.println( )  } } 

Edit this now to display our "No worries." text (you'll see that code assist adds the closing quotation mark automatically as you type):

 public class Ch01_01 {     public static void main(String[] args)     {  System.out.println("No worries.")  } } 

However, Eclipse displays this new code with a wavy red line under it, which indicates there's a problem. To see what's going on, rest the mouse cursor over the new code, and a tool tip will appear, as you can see in Figure 1-13, indicating that there's a missing semicolon at the end of the line.

Figure 1-13. Checking an error

Add that semicolon now to give you the complete code and make the wavy red line disappear:

 public class Ch01_01 {     public static void main(String[] args)     {  System.out.println("No worries.");  } } 

Our code is complete. In Figure 1-13, note that the Package Explorer is giving us an overview of the project, showing the public class Ch01_01 and the main method in that class. In this way, the Package Explorer view gives you access to all the items in a project. To bring an item up in a code editor, just double-click it in the Package Explorer view.

Another handy way to find all the members of a class or object is to highlight an item's name in a code editor, right-click the highlighted name, and select the Open Type Hierarchy item from the context menu. Doing so will open the item's complete type hierarchy in the Hierarchy view, and you'll see all its members, the data types of fields, the arguments you pass to methods, and more. In fact, the code where the selected item is defined will also appear in a code editor (unless that code is inaccessible, as when it's in a JAR filefor example, the System.out class is defined in rt.jar , so no source code is availablealthough there are now ways to attach source directories to JAR files).

As you can see in this example, the coding was made a little easier because code assist knew all the members of the System.out class and let you select from among them. Code assist will automatically appear when you type a dot (.). You can also make code assist appear at any time while you're typing codejust type Ctrl+Space.

You can also turn code assist off. To configure code assist as you like, select Window Preferences, then Editor in the left pane of the Preferences dialog, and then the Code Assist tab.

Each time you edit the code in a file, as we're doing here in Ch01_01.java , an asterisk appears in front of the filename file in its code editor tab, as you see in Figure 1-13. This asterisk indicates that changes to the file have not yet been saved. There are many ways to save your work: click the diskette icon (for Save) in the toolbar; click the diskette followed by an ellipsis ( . . . ) icon (for Save As . . . ) in the toolbar; right-click the code itself and select the Save context menu item; or select the Save, Save As, or Save All menu items in the File menu.

Alright, we've got our first code written and stored to disk. How about running it?

1.5.4 Running Your Code

If you look closely at the Package Explorer view in Figure 1-13, you'll see that the circled C icon for our Ch01_01 class also has a small running figure in it. That is Eclipse's way of indicating this class is runnable because it has a main method. To run this code and see the output, select the Run Run As Java Application menu item, or open the pull-down menu for the running figure icon in the toolbar and select the Run As Java Application menu item. This runs our code (Eclipse will ask you to save it first if the code has not been saved yet), and the System.out.println method will write our message to the console. The text of that message, "No worries.", appears in the Console view at the bottom of the Java Perspective, as you see in Figure 1-14.

Figure 1-14. Running our Ch01_01 example

Congratulationsnow you're an Eclipse developer.

1.5.5 Using the Scrapbook

There's another way to run code in a Java Project, and you don't need a main method to do it: you can use a scrapbook page instead. Scrapbook pages give you a way of executing code, even partial code, on the flya big help in the development process. This is not an essential skill, but it's a useful one.

To create a scrapbook page, select the File New Scrapbook Page menu item to open the New Scrapbook Page dialog box, enter the name Ch01_01Scrapbook in the File name box, and click Finish to create the new scrapbook page, which will be saved as Ch01_01Scrapbook.jpage . The new page appears in the Package Explorer and is automatically opened in the editor view, as you see in Figure 1-15. You can enter code or code snippets to run in this page, which helps when your code is getting long and you just want to test part of it. For example, to run our example, enter this code in the scrapbook page (as you see in Figure 1-15)note that you must include the package name here when referencing the main method in your code:

 String[] args = {}; org.eclipsebook.ch01.Ch01_01.main(args); 
Figure 1-15. Using a scrapbook page

To tell the scrapbook page what code to run, select all the code you've entered, as you see in Figure 1-15, right-click it, and select the Execute context menu item (you can also select the Run Execute menu item). The results appear in the Console view as before, as you can see in Figure 1-15. In this way, you can execute Java code using a scrapbook page, even snippets of code, and see the results as they'd appear in the console. To close the scrapbook page, click the X button in the tab corresponding to its editor in the workbench's central pane.

If you select the Display item instead of the Execute item, you'll see the net return value of the code you've highlighted in the scrapbook, which is useful for testing methods on the fly. Also, note that you can set imports for the scrapbook page, importing other packages as needed, by right-clicking the scrapbook's code in the editor view and selecting the context menu's Set Imports menu item.

As you can see, the JDT are very helpful. There's also a lot morefor example, what if you've got an error in your code? Eclipse can help here, too.

ISBN: 0596006411
EAN: 2147483647
Year: 2006
Pages: 114
Authors: Steve Holzner

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