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Editing Java programs with the BlueJ IDE

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• Working environments to develop (= write) programs
  • There are 2 ways to develop (write) computer programs:

    Using an editor (e.g. gedit) and a compiler (such as javac) separately. You have seen this method in the last webnote --- click here Using an editor and a compiler in an integrated manner

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  • In the second way, you will need to install a special application called an Integrated Development Environment (IDE)

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• Java IDEs
  • There are a number of Intergrated Development Environment IDE) available for Java

  • Java IDEs:

    Eclipse -- Eclipse is highly extensible and customizable, but hard to learn (freely available) NetBeans -- created by Sun MircoSystem (original designer of the Java programming language) (freely available) JBuilder -- top commercial Java IDE; very costly... BlueJ -- easy to learn (freely available)

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  • In this webnote, you will learn to edit Java programs with BlueJ

  • In the next webnote, you will learn how to:

    compile the Java program with BlueJ run the (compiled) Java program with BlueJ

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  • You will learn how to program in the Java programming language later in this course

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  • BlueJ is freely available and it can be obtained from this website: click here

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• Preparation
  • Before you can use BlueJ, you must:

    Login to a computer in the MathCS lab Open a terminal window Change the current (working) directory to your cs170 directory This directory is used to store CS 170 labs and homeworks.

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• Information about this BlueJ tutorial
  • The tutorial is described from the perspective of the user cheung

    (Because it was developed by Professor Cheung)

  • The directory used to hold the project is /home/cheung/cs170

    For clarity, I have delete all files and folders from my cs170 directory.

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  • We will write a simple Java program and store the program in a project directory called "TestProj".

    The "TestProj" will be contained inside the /home/cheung/cs170 directory.

    In other words, the absolute path of the project directory is:

    /home/cheung/cs170/TestProj

  • Here is the Simple Java program that you will enter into BlueJ:

    public class Hello { public static void main(String[] args) { System.out.println("Hello Class"); System.out.println(" How is everyone doing so far ?"); } }

    You don't need to understand this program right now; it will be explained later in the course.

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• Topics covered in this (short) tutorial
  • Things you need to learn to get started with BlueJ

    Run the BlueJ application Create a new project in BlueJ Create a new program file Insert text into the file Delete text from the file Goto a certain line in the file Search for a pattern in the file Search and replace for a pattern with another pattern in the file Undo a change Save your work Quit without saving (because you made a mess)...

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• Starting the BlueJ IDE application
  • Enter the following command in a terminal window:

    UNIX prompt>> bluej &

    This will run BlueJ as a detached process

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    You will first see an announcement window:

    When it's ready, you will see the main window:

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• Create a new project
  • BlueJ requires that each project be stored in a different directory

    When you create a new project, BlueJ will also create a new directory for you.

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  • How to create a new project:

    Left click on the Project tab Then left click on the New Project tab: A new window will pop up: Enter the name of the new project directory (/home/cheung/cs170/TestProj) and click on the Create button: When BlueJ has successful created an new project, it will show the following window:

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• Create a new program file
  • Suppose we want to create a file that contains the following Java program (given above):

    public class Hello { public static void main(String[] args) { System.out.println("Hello Class"); System.out.println(" How is everyone doing so far ?"); } }

    Notice that the program is called class Hello

    This will be important in the creation procedure.

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  • How to create a Java program file:

    Left click on the New Class button: A new window will pop up: Type in the name of the "class" (which is Hello) and click OK: A new window will pop up: Final result: You can see the new file Hello in the TestProj area.

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  • To see that BlueJ has created a file, we list the content of the TestProj directory from a terminal window:

    The icon named Hello in BlueJ represents the program file Hello.java inside the TestProj directory.

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• Open a program file for editing
  • If you want to edit a program file, do the following:

    Right click on the file icon Then left click on the Open Editor button:

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  • A new window will pop up:

    The new window contains the content of the file Hello.java

    (To verify, use "cat Hello.java" in a terminal window)

    BlueJ has already inserted a few things in the file Hello.java to help you start writing a Java program

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• Deleting text from a file
  • How to delete text from a file:

    Highlight the text in BlueJ that you want to delete: Press the backspace key You can also press the delete key or control-X Result:

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• Inserting text into a file
  • How to insert text from a file:

    Use the scroll bar on the right to find the location in the file where you want to insert text. Left click at the insert location Then type in the new text. Example:

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• Insert text by copy and paste
  • You can insert text from another window into the document in BlueJ by using the copy and paste facility:

    Highlight any text in a window (e.g., from a webpage) The highlighted text is automatically copied in UNIX (On a Windows-based PC, you need to type control-C to copy) Now click in the BlueJ window at the position where you want to insert the highlighted text Type control-V (for paste)

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• Replacing some text
  • How to replace text:

    Delete the text Insert new text

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• Undo a change
  • When you make a edit mistake, you can undo the last change with the undo-command:

    control-Z

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  • Undo earlier changes:

    You can undo earlier changes by pressing control-Z multiple time The maximum number of changes can be undo is 25

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• Undo an "undo"
  • Suppose you have undone a change that was in fact correct

  • You can undo an undo operation using:

    control-Y (this is called a Redo operation)

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• Goto a certain line in the file
  • A feature that is very useful when you write computer programs is:

    Goto a certain line in a file

    That is because compilers (an application that translates a program written in a high level language into machine code) always report an error along with the location (as a line number) in the file.

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  • How to go to line number n in a file:

    Left click on the Tools tab Then left click on the Go to Line tab Example: After this, a window will pop up and you can enter the desired line number

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  • Keyboard shortcut:

    The keyboard shortcut for the Go to Line function is control-L

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• Search for a text pattern
  • Finding the next occurrence of a pattern in a file:

    Left click on the Find tab The lower portion of the BlueJ window will change to the Find menu Example: Enter the search text pattern and click Next: The text highlighted in yellow is the next matching pattern All other matching patterned are highlighted in blue

    Left click on the Next button to find the subsequent matching pattern

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  • Search forward:

    Left click on the Prev button to search forward

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• Search and Replace
  • Finding the next occurrence of a text pattern in a file and replace it with some other pattern:

    Left click on the Replace tab The lower portion of the BlueJ window will change to the Replace menu Example: Enter the replacement pattern in the Replace field: Click on the Once button to replace the current occurrence (in yellow): You can replace the next occurrence by clicking on Once another time. Click on All to replace every occurrence

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  • Hint:

    If you do not want to replace the current occurrence and want to continue the Search and Replace operation, then do the following: Click on the text immediately after the current occurrence Click Next (to find the next occurrence) Continue with replace if desire Example: Click on the text immediately after the current occurrence Click Next Continue with the Replace operation if so desired.

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• Saving the changes
  • Auto saving:

    You do not need to save your work. When you quit (close) the BlueJ window, it saves your works automatically

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  • Save your work explicitly:

    You can choose to save your work explicit by clicking of Class and then Save:

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• Quit without saving your work...
  • You do not have this option in BlueJ

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• Exit BlueJ
  • Before you exit BlueJ, I would recommend that you save all your changes explicitly

    You have learned saving your work above !!!

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  • Exiting BlueJ:

    To exit BlueJ, click Project in the BlueJ's main window and select Quit:

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