Java Arrays, Objects, Methods

CS 161 - Java

Saving Multiple Student Objects

Source: examples/CSClass.java



/** A class that will make use of another class.

 **/

public class CSClass {

 

  public static void main(String[] args) {

    if (args.length == 0) {

      System.out.println("usage java CSClass [student names]");

    }

    else {

      int numberOfStudents = args.length;

      CSClass cs161 = new CSClass( numberOfStudents );

      cs161.enroll( args );

      cs161.assignLabPartners();

      cs161.listRoster();

    }

  }

 

  // Instance fields

  CSStudent students[] = null;

  int last = 0;

 

  public CSClass( int number ) {

    students = new CSStudent[ number ];

  }

 

  public void enroll(String[] names) {

    int numberOfStudents = names.length;

    int id = 0;

 

    for (int arg = 0; arg < numberOfStudents; arg++) {

 

      String name = names[arg];

 

      id++;                             // assign next id

      String idString = String.valueOf(id); // as a String

 

      CSStudent aStudent = new CSStudent( name, idString);

 

      aStudent.setGrade(100);

 

      // save the reference to the current student in the next array slot

      students[last] = aStudent;

      last++;

    }

  }

 

  public void assignLabPartners() {

 

    // Assign every other pair of students as lab partners

    int next = 0;

    int pairs = last / 2;

    while (pairs > 0) {

        students[next].setLabPartner( students[next+1] );

        students[next+1].setLabPartner( students[next] );

        next += 2;

        pairs--;

    }

 

    // If there were an odd number of students in the array the

    // last one won't have a lab partner.

  }

 

  public void listRoster() {

    for (int i = last - 1; i >= 0; i--) {

      //  Ask each Student to identify itself, last to first

      System.out.println(students[i]);

    }

  }

}

Source: examples/CSStudent.java



/** Encapsulate information relating to a single student.

 ** @author: Jonathan Doughty

 **/

 

public class CSStudent {

 

  // Instance variables (fields) that will be associated with

  // each student

 

  private String GMU_Id;

  private String name;

  private int    homeworkGrade;

  private CSStudent labPartner;

 

  // Constructors for the class

 

  private CSStudent() { // why do you think this is?

  }

 

  public CSStudent( String name, String id) {

    this.name = name;

    GMU_Id = id;

  }

 

  // An accessor method to set the Student's name field; not

  // needed any more but left in because a student's name could

  // change.

  public void setName( String studentName ) {

    name = studentName;

  }

 

  // An accessor method to return this Student's name

  public String getName() {

    return name;

  }

 

  // An accessor method to set the Student's GMU_Id field (probably

  // no longer necessary)

  public void setId( String id ) {

    GMU_Id = id;

  }

 

  // An accessor method to set the Student's homeworkGrade field

  public void setGrade( int grade ) {

    homeworkGrade = grade;

  }

 

  // An accessor method to assign this Student's lab partner

  public void setLabPartner( CSStudent s ) {

    labPartner = s;

  }

 

  // Using the toString method to enable an instance of an

  // object to identify itself usefully.

  public String toString() {

 

    // Since I'm going to be returning a String made up of various

    // pieces, I build up those pieces in a StringBuffer.

 

    StringBuffer sb = new StringBuffer();

    sb.append(name);

    sb.append(" Id# ");

    sb.append(GMU_Id);

    if (labPartner != null) {

      // Notice I don't just use labPartner.toString().  If I did

      // I would create an infinite loop: each lab partner calls

      // its lab partner's toString() which calls's its lab

      // partner's toString() ...  Instead, I just get and append

      // the lab partner's name.

      sb.append(" lab partner=");

      sb.append( labPartner.getName());

    }

    return sb.toString();

  }

}

jwd