Introduction to Eclipse

Overview

Advantages of Eclipse over DrJava

• Project management
• Good debugger
• Error checking features (e.g. error checking as you type, suggestions to fix compile errors, ...)
• Auto complete feature (e.g. if you type "referenceVariable.", lets you choose a method/field from the variable's class from a drop down list)

How to Set Up Eclipse

• In the Unix Labs, eclipse 3.0 is with Java 1.5 is already installed.
• For your home computers you can download Eclipse from http://www.eclipse.org/downloads/index.php. You will need to download the version for Java Developers, not Java EE Developers.

How to Run Eclipse

• The first time you run it, you will be asked several questions about setting up your workspace. We suggest keeping the default settings. Once you complete the initial setup, you will be introduced with a Welcome screen which you can skip.
• Eclipse is designed around views called perspectives. The first time you start Eclipse, you will be in Resource perspective. We will be seeing Java and Debug perspectives in this tutorial.

Working with Projects

• Your workspace is divided in to projects.
• A project is a collection of source files, documentation, and other related files.
• Suggestion: create a separate project for each homework and lab.
• To create a project; choose File -> New ->Project. Choose Java Project, then choose a name and a directory.
• After creating a project, you will see it listed in the Package Explorer section.
• If you already have Eclipse projects, you can import them in to the current workspac by choosing File -> Import.

Browsing a Project

• If you expand a project in Package Explorer, you will see packages included in the project and the libraries it uses. Default package contains every class that is not included in any package.
• To add libraries to your project that you will use such as provided jar files, go to Project Properties by doing a right click on project name. From properties screen, go to Java Build Path. Here you can add all required libraries.
• As you expand a source file, you will see a list of its classes, and a list of methods in each class and so on. This can help you lookup a method quickly if needed. You can also use the outline pane as you are writing code to have a quick list of accessible methods.
• To create a class or interface in a project, you can choose File -> New -> Class or Interface. If your class is extending another class or implementing an interface, Eclipse will automatically place method declarations for you.

Helpful Features While Coding in the Code Pane:

• Auto complete in methods: As you write your code, you will be presented with a list of possible choices.
• Error checking as you type: Errors will be underlined red in your code. One thing to note here, eclipse will mark your code incorrect as you are typing it. Once you complete the line, it should go away unless your code is really incorrect.
• Easy commenting: If you're on a method signature, you can press Alt+Shift+J to insert javadoc comments.
• Auto indent any piece of code by selecting it and pressing Ctrl+I.
• Auto-compile: your files will be compiled automatically each time you save them. If an error exists in your files, you will see a red mark by the file name in Package Explorer. Also, the Error Pane located at the bottom will give you a list of errors occurred during last compilation. You can double click an error to go to its location.

Running your code

• Unlike DrJava, eclipse is only able to execute classes with main methods. To do so, open the Context Menu on the file name and choose Run As -> Java Application. You will see the output in Console pane.
  
  Alternatively, you can press Alt+Shift+X, J to run the file that is currently being edited.
• If you want to have more options such as sending arguments, you can choose Run... instead of Java Application.

Debugging

1. Create a new project and create a new class called DebugLab in the project.
2. Copy the contents of the DebugLab.java< file to that class (or alternatively copy DebugLab.java< to the directory of the project and refresh the project).
3. You will set breakpoints to suspend the execution of your program. To add a breakpoint to any line in the code, press Ctrl+Shift+B while you are on that line. (Alternatively, choose Run -> Toggle Breakpoint from the menu.) For our purposes, add a breakpoint to the line that has the debug method.
4. For debugging to work, you have to run your program in Debug mode. To do that you can press Alt+Shift+D, J or choose Debug As -> Java Application from the context menu. Once you run your program, it will execute up to first breakpoint it encounters and stop at that point, Eclipse will ask you to switch to Debug perspective automatically as it happens.
5. Debug perspective contains a call stack at the top left corner, a summary of variables in top right corner. You can also get a list of breakpoints at the same place. At the bottom, you can see the console which will show any output.
6. Our aim will be to analyze the values of Useless object u and the integer array a. There are several ways to do this:
• You can highlight u in the code panel and choose Inspect from the context menu. This will open a small window listing all instance variables of u.
• From the variables panel at the top, you can expand u and get a list of its instance variables.
• As the last option, you can add an expression to be watched. In order to do that, you have to open Expressions window by choosing Window -> Show View -> Expressions. This will open a new tab on top right corner. You can right click anywhere on that tab and choose Add Watch Expression, any expression you type here will be watched throughout the debugging process. For example you can type u.a to watch a field of Useless object u. Note that this only works as long as the object that's being watched is in scope.
• Similarly, you can repeat all of the above to view any index of array.
7. You also have different options to continue running your code. You can access the buttons explained below on the Debug pane.
• Resume (F8): Resumes your program until the next breakpoint or until the end of execution.
• Step Into (F5): Only executes one line in the program. If the current line is a method call, it will go into that method. For example, if you do Step Into at our current breakpoint, your program will stop at the first line of debug method.
• Step Over (F6): Only executes one line in the program. If the currently line is a method call, it completes the execution of that method and goes to next line. It doesn't go into the called method like Step Into. So if you do a step over at the current breakpoint, it will execute debug method and goes to next line which is the end of the program.
• At any time, you can terminate the execution of the program by pressing Terminate button.