CS1027b Computer Science Fundamentals II

Lab 1

Learning Outcomes

Upon completion of this lab, you should be able to do the following in Eclipse:

Create a new project containing new source files.
Create a new project from existing source files.
Import java libraries to your program.
Create a simple java program that can read input from the keyboard and perform simple calculations.

General Lab Instructions to Help Labs Run Smoothly

Read through the lab instructions before coming to the lab.
Do the pre-lab preparation.

Overview and Preparation

In this course we will use Eclipse as the Integrated Development Environment. Eclipse has been installed on the Computer Science Department machines in the Undergrad Labs used as the First Year Teaching Environment (MC 8, 10, 230, 235).

You can download Eclipse for your own computer from the Eclipse Website. Read the tutorials and information posted in the course's webpage about how to install java and Eclipse on your computer.
If you have not used Eclipse, you may want to read the Workbench User Guide in the on-line help which comes with Eclipse (on the top menu, select "Help" and then select "Help Contents").

IMPORTANT. Make sure you attend your lab session, sign the attendance sheet, show the result(s) of each exercise to your TA, and submit your .java files through OWL by 11:55pm on the same day as your lab session to get your marks for the lab.

Suggested Project Organization

In Integrated Development Environments such as Eclipse, Netbeans, VisualStudio, etc. we need to create a project in order to run a program. Most programs consist of multiple files. A project contains all the information about the program, such as a list of program files (source files, class files) and IDE settings. You will create a new project in Eclipse for every program that you wish to run.

Create a folder called (for example) Eclipse or CS1027b to hold all your Eclipse projects for this course. This folder will contain the project files themselves. The Java source files may be in this folder also (as in Exercises 1 and 3), or in some other (external) folder (as in Exercise 2).

Exercise 1: Getting Started with Eclipse

Start up Eclipse. You may get the Welcome window first; close it and you will see the Java workbench. The editor area is in the middle.
You will be asked to select a workspace location; the workspace is the area in which all your Eclipse projects will be stored. Select the folder that you previously created for this purpose.
You can also select the workspace location by selecting "File" from the top menu and then "Switch Workspace".
We will start by creating a new Java project in Eclipse. Select File, New, Java Project from the top menu. Enter the project name: HelloWorld. Note that the default selections are "Use default location" and "Create separate folders for sources and class files". (Leave these as they are.) Click on Next at the bottom of the window, and then Finish at the bottom of the next window. You should now see your HelloWorld project in the Package Explorer window.
Select project HelloWorld by clicking on it.
To create a new program, select File, New, Class from the top menu. For the name of the class enter HelloWorld.
Select "public static void main (String[] args)" from the method stubs. This will add a method called main in your class. When executing a java program the java interpreter will start execution at method main; therefore, every java program must have a main method.
Click on Finish.

Type what you need so that the following program is in the editor window:

public class HelloWorld {
    public static void main(String[] args) {
         System.out.println("Hello World!");
    }
}

Save your work by selecting File, Save, or by clicking the Save icon in the tool bar.

Add line numbers to the source view by right clicking on the editor window and selecting Preferences. Follow the link to the Text Editors page that is in the first sentence (or in the left hand section, select General, Editors, Text Editors). In the Text Editors page, check Show line numbers. Click on OK or on Apply and Close.
To properly indent your code, you can press at the same time the keys Ctrl, Shift and F in your keyboard. You can also select "Window" from the top menu and then Preferences->Java->Editor->SaveActions and check the "Format source code" option. This will format your code every time you save it.
Run your program by selecting Run, Run As, Java Application from the top menu or by selecting the Run icon (the green circle with a white triangle inside) in the tool bar. Save resources, if asked to. There should now be a Console window at the bottom of the workbench in which Hello World! appears as the output of the program.
To close your project, right click on the HelloWorld project icon in the Package Explorer window, and select Close Project.
To reopen the project again, right click on the HelloWorld project icon and select Open Project.
To bring HelloWorld.java to the editor again, click on the ">" symbol on the left of the icon for "HelloWorld" in the Package Explorer. Then click on the ">" beside the "src" icon, and then click on the ">" beside the "(default package)" icon. Finally double click on the "HelloWorld.java" icon.
Close the project again.

Exercise 2: Creating a New Project from Existing Source Files

In this exercise, you will create a new project to run the sample Social Networking application whose files are posted on the sample code section of the CS1027 Course web page. (We will not concern ourselves with what this code does at present; you will merely use the files to practice this part of the Lab.)

Create a new folder in your disk area called SocialNetworking; do not create the folder inside your workspace folder. Download the four .java files from the "Object Oriented Programming" section of the sample page, and store them into that folder.
In Eclipse, select File, New, Java Project from the top menu. Enter the project name: SocialNetworking.
Uncheck "Use default location", and browse to find the folder where you stored the above java files. Click Finish at the bottom of the window.
Go to the Package Explorer window and select the SocialNetworking project by clicking on the ">" symbol to its left. Then select "(default package)" by clicking on the ">" symbol to its left.
You will get a compiler error from MyFriends.java (the little red "X" at the bottom left corner of the icon for MyFriends.java), since the provided code does not yet have the getNumFriends() method defined in SocialNetwork.java. Double click on the MyFriends.java icon. To fix this error, comment out the offending line of code in MyFriends.java (add "//" at the beginning of the line marked with the little red "X"; this indicates that everything after the "//" is a comment)
Run the program. The results should be visible in the Console window located below the Editor window.
The output of the program should be a list of contacts and their email addresses.
Close the project.

Exercise 3: Creating a New Java Program

Create a new java project called MyName in your project folder.
Create a new class called MyName that has a main method which displays your name and email address on the screen.
Run your MyName program and make sure it works correctly.
Close the project.

Exercise 4: Creating a Simple Calculator

Create a new java project called SimpleCalculator in your project folder.
Create a new class called Calculator with a main method.
Add to your new class the line
import java.util.Scanner;
before the line
public class Calculator {
This will tell java to include the library called java.util.Scanner to your program. This library contains java code that your program can use, among other things, to read user input from the computer keyboard.
Inside the main method do the following:
- Declare two integer variables x and y and one character variable c. The syntax for declaring an integer variable is
  int variable_name;
  and for a character variable
  char variable_name;
- Initialize c so it stores the character '+'.
- Add the following code after you have declared the variables
     Scanner input = new Scanner(System.in);
  Now, to read an integer from the computer keyboard and to store it in variable x you can use this code:
     x = input.nextInt();
  To read a character from the computer keyboard and store it in variable c you can use
     c = input.next().charAt(0);
- Add the following code after the code you entered in the last step:
  while (c == '+' || c == '-') { }
- Within the curly brackets { } of the while loop add code to perform the following steps:
  - Display a message on the screen asking the user to enter a number.
  - Read a number entered from the computer keyboard and store it in variable x.
  - Display a message on the screen asking the user to enter a second number.
  - Read a number entered from the computer keyboard and store it in variable y.
  - Display a message on the screen asking the user to enter an arithmetic operator '+' or '-'.
  - Read a character entered from the computer keyboard and store it in variable c.
  - Add the following code
    if (c == '+') System.out.println("Result = "+(x+y)); else if (c == '-') System.out.println("Result = "+(x-y));
Run your Calculator program and make sure it works correctly. The program must terminate when the arithmetic operator entered is different from '+' and '-'.
Close the project.