Eclipse -Introduction
In computer programming, Eclipse is
an Integrated development environment (IDE) comprising a base workspace and an
extensible plug-in system for customizing the environment. It is written mostly
in Java. It can be used to develop applications in Java and, by means of
various plug-ins, other programming languages including Ada, C, C++, COBOL,
Fortran, Haskell, JavaScript, Lasso, Perl, PHP, Python, R, Ruby (including Ruby
on Rails framework), Scala, Clojure, Groovy, Scheme, and Erlang. It can also be
used to develop packages for the software Mathematica. Development environments
include the Eclipse Java development tools (JDT) for Java and Scala, Eclipse
CDT for C/C++ and Eclipse PDT for PHP, among others.
The initial codebase originated
from IBM VisualAge. The Eclipse software development kit (SDK), which includes
the Java development tools, is meant for Java developers. Users can extend its
abilities by installing plug-ins written for the Eclipse Platform, such as
development toolkits for other programming languages, and can write and
contribute their own plug-in modules.
Overview
Until now, we've used DrJava
throughout your computer science education. Although DrJava with its
Interactions Pane is a nice IDE (Integrated Development Environment) for
introductory purposes, it lacks many of the features found in professional
quality IDE's, such as a good debugger and good large-scale project management
capabilities. In this lab we introduce a powerful IDE called Eclipse which you
will find to be a very useful tool, especially when working on large projects.
Like DrJava, Eclipse is free and multi-platform (unix, Mac, Windows).
What is Eclipse?
Eclipse started as a proprietary IBM product (IBM Visual age
for Smalltalk/Java)
Embracing the open source model IBM opened the product up
Open Source
It is a general purpose open platform that facilitates and
encourages the development of third party plug-ins
Best known as an
Integrated Development Environment (IDE)
Provides tools for coding, building, running and debugging
applications
Originally designed
for Java, now supports many other languages
Good support for C, C++
Python, PHP, Ruby, etc...
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
The eclipse debugger is powerful.
To learn it we'll debug DebugLab.java, which contains a DebugLab class with a
simple method and a very simple Useless class. We will set breakpoints (at
lines of code where we want Java to pause during execution so we can examine
the values of variables and so forth).
·
Create a new project and create a new class
called DebugLab in the project.
·
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).
·
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.
·
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.
·
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.
·
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.
·
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.
