My First Program Eclipse

Laboratory 1 Prepared by: Dr. Constandinos X. Mavromoustakis

Date: 2011

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University of Nicosia, Cyprus COMP 212- Object Oriented Programming

Fall 2011

Title and objective of the Laboratory:

Creating your first Java project and your first program


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Creating your first Java project and your

first program

The following will describe how to create a minimal Java program using Eclipse. It will

be the classical "Hello World" program. Our program will write "Hello Eclipse!" to the

console.

Create project

Select from the menu File -> New-> Java project. Maintain a sample name

"de.vogella.eclipse.ide.first" as the project name. Select "Create separate source and

output folders".


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Press finish to create the project. A new project is created and displayed as a folder. You

can now open the folder "de.vogella.eclipse.ide.first"

Create package

Create now a package. A good convention is to use the same name for the top package as

the project. Create therefore the package "de.vogella.eclipse.ide.first".


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Select the folder src, right mouse click on it and select New -> Package.

Create Java class

Right click on your package and select New -> Class

Create MyFirstClass, select the flag "public static void main (String[] args)"

first.program/src

first.program


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Write down now the following code:

package first.program;

public class MyFirstClass {

public static void main(String[] args) {

System.out.println("Hello Eclipse!");

}

}

first.program/src

first.program


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Run your project in Eclipse

Now run your code. Right click on your Java class and select Run-as-> Java application

Done! You should see the output in the console of eclipse.

first.program


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Multiple choice exercise

Given:

2. public class Choosy {

3. public static void main(String[] args) {

4. String result = "";

5. int x = 7, y = 8;

6. if(x == 3) { result += "1"; }

7. else if (x > 9) { result += "2"; }

8. else if (y < 9) { result += "3"; }

9. else if (x == 7) { result += "4"; }

10. else { result += "5"; }

11. System.out.println(result);

12. }

13. }

What is the result? (Choose all that apply.)

(circle the correct answer)

A. 3

B. 34

C. 35

D. 345

E. Compilation fails due to an error on line 5.

F. Compilation fails due to errors on lines 8 and 9.


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G. Compilation fails due to errors on lines 7, 8, and 9.

Another Programming exercise Lab #1 File name: GalToLit.java

Converting Gallons to Liters

Although the preceding sample programs illustrate several important features of the Java

language, they are not very useful. Even though you do not know much about Java at this

point, you can still put what you have learned to work to create a practical program. In

this project, we will create a program that converts gallons to liters. The program will

work by declaring two double variables. One will hold the number of the gallons, and the

second will hold the number of liters after the conversion. There are 3.7854 liters in a

gallon. Thus, to convert gallons to liters, the gallon value is multiplied by 3.7854. The

program displays both the number of gallons and the equivalent number of liters.

Step by Step

1. Create a new file called GalToLit.java.

2. Enter the following program into the file:

/* Project 1-1 This program converts gallons to liters.

Call this program GalToLit.java.

*/

class GalToLit {

public static void main(String args[]) {

double gallons; // holds the number of gallons

double liters; // holds conversion to liters


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gallons = 10; // start with 10 gallons

liters = gallons * 3.7854; // convert to liters

System.out.println(gallons + " gallons is " + liters + " liters.");

}

}

3. Compile the program using the following command line:

C>javac GalToLit.java

4. Run the program using this command:

C>java GalToLit

You will see this output:

10.0 gallons is 37.854 liters.

5. As it stands, this program converts 10 gallons to liters. However, by changing the

value assigned to gallons, you can have the program convert a different number of

gallons into its equivalent number of liters.

Another Programming exercise Lab #1 File name: GalToLitTable.java

Improving the Gallons-to-Liters Converter

You can use the for loop, the if statement, and code blocks to create an improved version

of the gallons-to-liters converter that you developed in the first project. This new version

will print a table of conversions, beginning with 1 gallon and ending at 100 gallons. After

every 10 gallons, a blank line will be output. This is accomplished through the use of a


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variable called counter that counts the number of lines that have been output. Pay special

attention to its use.

Step by Step

1. Create a new file called GalToLitTable.java.

2. Enter the following program into the file.

/*

This program displays a conversion table of gallons to liters. Call this program

"GalToLitTable.java". */

class GalToLitTable {

public static void main(String args[]) {

double gallons, liters;

int counter;

counter = 0;

for(gallons = 1; gallons <= 100; gallons++) {

liters = gallons * 3.7854; // convert to liters

System.out.println(gallons + " gallons is " + liters + " liters.");

counter++;

// every 10th line, print a blank line

if(counter == 10) {

System.out.println();

counter = 0; // reset the line counter

}

}

}


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}

3. Compile the program using the following command line:

C>javac GalToLitTable.java

4. Run the program using this command:

C>java GalToLitTable

Here is a portion of the output that you will see:




















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Another multiple choice exercise

Which of the following variable names is invalid?

A. count

B. $count

C. count27

D. 67count

Write a Java program where you prove each one of the above variables’ validity.

Next lab session: Read from Keyboard and user-inputer and interaction

My First Program Eclipse

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