Microsoft Word - Lab_6.docxMicrosoft Word - Lab_6.docx

Files Lab Six in Java

 

Microsoft Word - Lab_6.docx

Problem description

You are given a text file called 'Students.txt' that contains information on many students. Your program reads the file, creating many Student objects, all of which will bestoredintoanarraylistofStudentobjects,intheStudentsclass. TheTesterclass controls everything, calling many Students class methods to produce lots of different outputs. The program must write the output to an output file and to the Terminal Window.

File and class specifications

Students.txt file format
Information for each student is stored in the file as 3 lines of text:

name age GPA

e.g. the following shows data for two students:

Name0
22
1.2
Name1
22
2.71

 

Student class
The Student class has instance variables and methods to represent one single student.

Your Student class must have exactly and only the following instance variables:

private String name;
private int age;
private double gpa;

Microsoft Word - Lab_6.docx

Design appropriate constructors and other methods for your Student class, including: + toString() – returns a String containing the 3 instance variables e.g.

Name0 22 1.2

 

Students class
Very importantly, the Students class is used to store and process many Student objects. It will have an instance variable to store many Student objects. Methods intended to process many Student objects belong in this Students class.

Your Students class must have exactly and only the following instance variable: private ArrayList<Student> students;

students here is an array list of Student objects, in which all of the Student objects are stored.

Students must have appropriate constructors and methods, including the following: + readFile() – opens the data file, reads the data, creates Student objects, and adds

them to the students array list
+ toString() – returns a String containing a line of information for each Student in

thestudentsarraylist. WillcallStudent'stoString()todothis. Forexample:

1. Name0  22 1.2
2. Name1  22 2.71

Many other methods for processing a Students object. Most of the code you write will

be in this class.

 

Reading the data file
Your program will use the Scanner class to read from the data file, as demonstrated during the Week 13. Files lecture.

 

Writing the output file
Your program must use the PrintWriter class to save all its output to the output.txt file, as demonstrated during the Week 13. Files lecture. It will also send the same output to the BlueJ Terminal Window, as usual.

 

Tester class

The Tester class controls everything. Tester does not have any instance variables. You have to write the Tester class.

Tester contains only a main() method, which first creates a single Students object (and aPrintWriterobject). TheStudentsobjectthencallsaseparateStudentsmethodto do each of the 6 different tasks below. You must design appropriate parameters and return values, in particular so that all program output to Terminal Window and output.txtisdonefrommain(). Inpseudocode:

+ main()
create an empty Students object
create a new PrintWriter object to create the ‘output.txt’ output file

read data file into Students
print all Student objects from Students
print the Student with the best GPA
calculate and print the average GPA
print the youngest Student who has a GPA below average print just the names of all the students

 

Hints

• -  the Students.txt data file is available at Blackboard, Course Documents, Week 14 folder, Example programs. You must copy it into your Lab 6 BlueJ project folder
• -  you will need to add throws IOException to your Tester class main() method headerandtheStudentsclassreadFile()methodheader. For example, in Tester:

     public static void main(String args[]) throws IOException

  This prevents a file handling syntax error: “unreported exception java.io.IOException; must be caught or declared to be thrown”
• -  (you may want to review array lists from Blackboard, Course documents, Week 7 Arrays and array lists)
• -  it is important in this lab always to keep in mind that each element in the Students class array list is itself an entire Student object...
• -  it is essential that you draw pictures of the objects involved in your program, so that you are always aware of the data type you are working with

Microsoft Word - Lab_6.docx

• - the 6 different actions above will each be implemented as a separate public Students method, called from main() by the Students object, using appropriate parameters and return types
• -  (by the way, there is no inheritance in this lab)

 

Microsoft Word - Lab_6.docxSyntax for processing an array list of objects

- the syntax for processing an array list of Student objects is exactly as you would

expect. For example, here’s a method that prints all the Students with GPAs above the average

• - first, the method call in main(). Since we must do all printing from main(), we design aboveAverage() to return a new Students object:

Microsoft Word - Lab_6.docx

• System.out.printf("nGPAs above the average of %.2fn", gpa);
        ot.printf("nGPAs above the average of %.2fn", gpa);
        System.out.println(students.aboveAverage(gpa).toString());
        ot.println(students.aboveAverage(gpa).toString());

• -  since aboveAverage() deals with many students, it would be part of the Students class. It creates a new Students object in which to return many Student objects:

Microsoft Word - Lab_6.docx

public Students aboveAverage(double avgGPA)

       {
           Students aboveAverage = new Students();

           for (int i = 0; i < students.size(); ++i) {
               if (students.get(i).getGPA() > avgGPA)

               aboveAverage.add(students.get(i));
           }

Microsoft Word - Lab_6.docx

return aboveAverage;
}

Microsoft Word - Lab_6.docx

•          
•   see that it calls a method getGPA(), that must directly return the GPA of a student. SogetGPA()wouldbepartoftheStudentclass: 

     public double getGPA()

• { return gpa; } 

           
•   it also calls a method add(), that takes a Student object and adds it to a Studentsobject. So add()would be part of the Students class:

Microsoft Word - Lab_6.docx

public void add(Student s)

{
    students.add(s);

}Microsoft Word - Lab_6.docx

Designing method return types
 the natural unit of an object-oriented program is an object. So methods returning

results tend to return entire objects. Some hypothetical examples to illustrate this:

•   e.g. bestStudent() returns a single student, so would return a Student object. Method header would be something like:

        public Student bestStudent(~~~~~~)
  

•   e.g. studentsAboveAverage() returns many students, so would return a Students object. Method header would be something like: public Students studentsAboveAverage(~~~~~~)
•   (of course methods can also return non-object data types if that is appropriate) e.g. averageGPA() returns the average GPA, so method header would be something like:

        public double averageGPA()