Java程序辅导

  
 
Laboratory 1 
Prepared by: Dr. Constandinos X. Mavromoustakis 
Date:  
2011 
1 
 
 
 
 
 
 
 
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 
 
 
  
 
Laboratory 1 
Prepared by: Dr. Constandinos X. Mavromoustakis 
Date:  
2011 
2 
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". 
  
 
Laboratory 1 
Prepared by: Dr. Constandinos X. Mavromoustakis 
Date:  
2011 
3 
 
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". 
  
 
Laboratory 1 
Prepared by: Dr. Constandinos X. Mavromoustakis 
Date:  
2011 
4 
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 
  
 
Laboratory 1 
Prepared by: Dr. Constandinos X. Mavromoustakis 
Date:  
2011 
5 
 
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 
  
 
Laboratory 1 
Prepared by: Dr. Constandinos X. Mavromoustakis 
Date:  
2011 
6 
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 
  
 
Laboratory 1 
Prepared by: Dr. Constandinos X. Mavromoustakis 
Date:  
2011 
7 
 
 
 
  
 
Laboratory 1 
Prepared by: Dr. Constandinos X. Mavromoustakis 
Date:  
2011 
8 
 
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. 
  
 
Laboratory 1 
Prepared by: Dr. Constandinos X. Mavromoustakis 
Date:  
2011 
9 
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 
  
 
Laboratory 1 
Prepared by: Dr. Constandinos X. Mavromoustakis 
Date:  
2011 
10 
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 
  
 
Laboratory 1 
Prepared by: Dr. Constandinos X. Mavromoustakis 
Date:  
2011 
11 
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 
       } 
   } 
} 
  
 
Laboratory 1 
Prepared by: Dr. Constandinos X. Mavromoustakis 
Date:  
2011 
12 
} 
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: 
1.0 gallons is 3.7854 liters. 
2.0 gallons is 7.5708 liters. 
3.0 gallons is 11.356200000000001 liters. 
4.0 gallons is 15.1416 liters. 
5.0 gallons is 18.927 liters. 
6.0 gallons is 22.712400000000002 liters. 
7.0 gallons is 26.4978 liters. 
8.0 gallons is 30.2832 liters. 
9.0 gallons is 34.0686 liters. 
10.0 gallons is 37.854 liters. 
11.0 gallons is 41.6394 liters. 
12.0 gallons is 45.424800000000005 liters. 
13.0 gallons is 49.2102 liters. 
14.0 gallons is 52.9956 liters. 
15.0 gallons is 56.781 liters. 
16.0 gallons is 60.5664 liters. 
17.0 gallons is 64.3518 liters. 
18.0 gallons is 68.1372 liters. 
  
 
Laboratory 1 
Prepared by: Dr. Constandinos X. Mavromoustakis 
Date:  
2011 
13 
19.0 gallons is 71.9226 liters. 
20.0 gallons is 75.708 liters. 
21.0 gallons is 79.49340000000001 liters. 
22.0 gallons is 83.2788 liters. 
23.0 gallons is 87.0642 liters. 
24.0 gallons is 90.84960000000001 liters. 
25.0 gallons is 94.635 liters. 
26.0 gallons is 98.4204 liters. 
27.0 gallons is 102.2058 liters. 
28.0 gallons is 105.9912 liters. 
29.0 gallons is 109.7766 liters. 
30.0 gallons is 113.562 liters. 
 
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