5.8 Άσκηση Αντικειμενοστραφούς Προγραμματισμού (συνέχεια)

© Γιάννης Κωστάρας

< Δ

Πλέον μπορούμε να εφαρμόσουμε όσα μάθαμε στα μαθήματα αυτής της εβδομάδας ώστε να απλοποιήσουμε την υλοποίηση του έργου School.

Υλοποίηση με το NetBeans

  1. Ανοίξτε το έργο School που δημιουργήσαμε στην προηγούμενη άσκηση από το μενού File -> Open Project ή File -> Open Recent Project αν δεν το έχετε ήδη ανοικτό.

Επαναλαμβάνουμε εδώ τον κώδικα των κλάσεών μας.

package school.validation;
/**
 * An Utility Validation class.
 */
public final class Validation {
    /** Max size for names. */
    private static final int MAX_SIZE = 20;
    /** Classroom name length. */
    private static final int CLASSROOM_NAME_LENGTH = 2;
    /** Classroom min size. */
    private static final int CLASSROOM_MIN_SIZE = 10;
    /** Classroom default/max size. */
    public static final int CLASSROOM_MAX_SIZE = 30;
    /** Identity length. */
    private static final int ID_LENGTH = 8;

    /**
     * No instance of this class are allowed.
     */
    private Validation() {
    }

    /**
     * A {@code name} is valid if it is neither {@code null} nor empty and 
     * not more than {@code MAX_SIZE}.
     * @param name a name
     * @return {@code true} if {@code name} is valid
     * @see MAX_SIZE
     */
    public static boolean isNameValid(String name) {
        return name != null && !name.isBlank() && name.length() <= MAX_SIZE;
    }
    
    /**
     * A valid age is between 15 and 18 years old. 
     * 
     * @param inAge an age
     * @return {@code true} if {@code inAge} is between the limits
     */
    public static boolean isAgeValid(int inAge) {
        return inAge >= 15 && inAge <= 18;
    }

    /**
     * A valid classroom size is between 10 and 30 pupils.
     * 
     * @param inSize classroom size
     * @return {@code true} if {@code inSize} is between the limits
     * @see CLASSROOM_MIN_SIZE
     * @see CLASSROOM_MAX_SIZE
     */
    public static boolean isSizeValid(int inSize) {
        return inSize >= CLASSROOM_MIN_SIZE && inSize <= CLASSROOM_MAX_SIZE;
    }

    /**
     * A valid classroom name should start with one of the letters {@code Α, Β, Γ}
     * and end with a number. E.g. {@code Γ1}.
     * @param classRoom a classroom name
     * @return {@code true} if {@code classRoom} is valid
     * @see CLASSROOM_NAME_LENGTH
     */
    public static boolean isClassRoomNameValid(String classRoom) {
        return classRoom != null && !classRoom.isBlank()
                && classRoom.length() == CLASSROOM_NAME_LENGTH
                && (classRoom.startsWith("Α")
                || classRoom.startsWith("Β")
                || classRoom.startsWith("Γ"))
                && classRoom.charAt(1) >= '1'
                && classRoom.charAt(1) <= '9';
    }
    
    /**
     * A valid Hellenic ID consists of two letters and six numbers. E.g. {@code XY123456}.
     * @param id a Hellenic ID number (ΑΔΤ)
     * @return {@code true} if the {@code id} is valid
     * @see ID_LENGTH
     */
    public static boolean isIdValid(String id) {
        return id != null && !id.isBlank() && id.length() == ID_LENGTH
                && isCapitalLetter(id.charAt(0))
                && isCapitalLetter(id.charAt(1))
                && isNumber(id.charAt(2))
                && isNumber(id.charAt(3))
                && isNumber(id.charAt(4))
                && isNumber(id.charAt(5))
                && isNumber(id.charAt(6))
                && isNumber(id.charAt(7));
    }

    /**
     * Check if {@code c} is a capital letter.
     * @param c character to check
     * @return {@code true} if {@code c} is capital letter.
     */
    public static boolean isCapitalLetter(char c) {
        return c >= 'A' && c <= 'Ω';
    }
    
    /**
     * Check if {@code c} is a number.
     * @param c character to check
     * @return {@code true} if {@code c} is a number.
     */
    public static boolean isNumber(char c) {
        return c >= '0' && c <= '9';
    }
}

package school;

import school.validation.Validation;

/**
 * Parent class of any person.
 */
public abstract class Person {
    /** The empty string used in case no name has been given. */
    static final String NONE = "<Κενό>";
    /** Person's first name. */
    protected String firstName = NONE;
    /** Person's last name. */
    protected String lastName = NONE;

    /**
     * Creates a new person. Is only called by subclasses.
     * 
     * @param firstName first name
     * @param lastName last name
     * @see school.validation.Validation#isNameValid
     */
    Person(String firstName, String lastName) {
        if (Validation.isNameValid(firstName)) {
            this.firstName = firstName.trim();
        }
        if (Validation.isNameValid(lastName)) {
            this.lastName = lastName.trim();
        }
    }

    /**
     * @return person's first name 
     */
    public String getFirstName() {
        return firstName;
    }

    /**
     * Set person's first name. 
     * 
     * @param firstName a new first name
     * @see school.validation.Validation#isNameValid
     */
    public void setFirstName(String firstName) {
        this.firstName = Validation.isNameValid(firstName) ? firstName.trim() : NONE;
    }

    /**
     * @return person's last name 
     */
    public String getLastName() {
        return lastName;
    }
    
    /**
     * Set person's last name. 
     * 
     * @param lastName a new last name
     * @see school.validation.Validation#isNameValid
     */
    public void setLastName(String lastName) {
        this.lastName = Validation.isNameValid(lastName) ? lastName.trim() : NONE;
    }

    @Override
    public String toString() {
        return ", firstName=" + firstName + ", lastName=" + lastName;
    }
}

package school;

import school.validation.Validation;

/**
 * A student of the school.
 */
public class Student extends Person {
    /** Automatic counter to set AM. */
    private static int amCounter = 0;
    /** Student's registration number (AM).*/
    private final int am;
    /** Student's age. -1 means age has not been set. */
    private int age = -1;  // 15-18
    /** Student's classroom. */
    private ClassRoom classRoom;

    /**
     * Constructor.
     * 
     * @param firstName student's first name
     * @param lastName student's last name
     * @param age student's age must be between 15 and 18 years old
     * @see school.validation.Validation#isAgeValid(int) 
     */
    public Student(String firstName, String lastName, int age) {
        super(firstName, lastName);
        am = ++amCounter;
        if (Validation.isAgeValid(age)) {
            this.age = age;
        }
    }

    /**
     * Student's AM is calculated automatically.
     * @return student's AM
     */
    public int getAm() {
        return am;
    }
    
    /**
     * @return student's age 
     */
    public int getAge() {
        return age;
    }

    /**
     * Set student's age. It increases every year.
     * @param age student's age.
     * @see school.validation.Validation#isAgeValid(int) 
     */
    public void setAge(int age) {
        this.age = Validation.isAgeValid(age) ? age : -1;
    }

    /**
     * @return the classroom the student is in.
     */
    public ClassRoom getClassRoom() {
        return classRoom;
    }

    /**
     * Set student's classroom.
     * @param classRoom new classroom for student.
     */
    void setClassRoom(ClassRoom classRoom) {
        this.classRoom = classRoom;
    }

    @Override
    public int hashCode() {
        int hash = 7;
        hash = 41 * hash + this.am;
        return hash;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj == null) {
            return false;
        }
        if (getClass() != obj.getClass()) {
            return false;
        }
        final Student other = (Student) obj;
        return this.am == other.am;
    }
    
    @Override
    public String toString() {
        return "Student{" + "am=" + am + super.toString() + ", age=" + age + ", classRoom=" + classRoom + '}';
    }
}

package school;

import java.util.Arrays;
import java.util.Objects;
import school.validation.Validation;

/**
 * A school teacher.
 */
public class Teacher extends Person {
    /** Max number of lessons a teacher can teach in the school. */
    private static final int MAX_LESSONS = 3;
    /** No ID number. */
    private String id = NONE;  // ΑΔΤ
    /** Lessons the teacher can teach. */
    private String[] lessons;
    /** How many lessons the teacher teaches. */
    private int index = 0;

    /**
     * Constructor.
     * 
     * @param id teacher's ID number
     * @param firstName teacher's first name
     * @param lastName teacher's last name
     * @param lessons a teacher can teach up to 3 lessons
     * @see MAX_LESSONS
     * @see school.validation.Validation#isIdValid(java.lang.String) 
     */
    public Teacher(String id, String firstName, String lastName, String... lessons) {
        super(firstName, lastName);
        if (Validation.isIdValid(id)) {
            this.id = id;
        }
        if (lessons != null && lessons.length > 0) { // αντιγράφουμε μόνο τα 3 πρώτα μαθήματα
            int length = lessons.length > MAX_LESSONS ? MAX_LESSONS : lessons.length;
            this.lessons = Arrays.copyOfRange(lessons, 0, length);
        } else {
            this.lessons = new String[MAX_LESSONS];
        }
    }

    /**
     * @return the teacher's ID number
     */
    public String getId() {
        return id;
    }

    /**
     * Set the teacher's id.
     * 
     * @param id the new ID number. It shouldn't be null.
     * @see school.validation.Validation#isIdValid(java.lang.String)
     */
    public void setId(String id) {
        this.id = Validation.isIdValid(id) ? id : NONE;
    }

    /**
     * Add a new lesson that this teacher teaches. If the number of lessons
     * that a teacher can teach is reached, the lesson is ignored.
     * @param lesson lesson to add
     */
    public void addLesson(String lesson) {
        if (lesson != null && index < MAX_LESSONS) {
            lessons[index++] = lesson;
        }
    }
    /**
     * Remove the lesson from the lessons that this teacher teaches. If the 
     * lesson is not teached by this teacher, it is ignored.
     * @param lesson lesson to remove
     */
    public void removeLesson(String lesson) {
        if (lesson != null) {
            remove(contains(lessons, lesson));
        }
    }
    
    /**
     * Checks if the teacher teaches this lesson.
     * @param les lesson to search for
     * @return {@code true} if the teacher teaches this lesson.
     */
    public boolean contains(String les) {
        return les == null ? false : contains(this.lessons, les) >= 0;
    }
    
    /**
     * @return the lessons that this teacher teaches. 
     */
    public String[] getLessons() {
        return Arrays.copyOf(lessons, index);
    }    

    @Override
    public int hashCode() {
        int hash = 3;
        hash = 59 * hash + Objects.hashCode(this.id);
        return hash;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj == null) {
            return false;
        }
        if (getClass() != obj.getClass()) {
            return false;
        }
        final Teacher other = (Teacher) obj;
        return Objects.equals(this.id, other.id);
    }

    @Override
    public String toString() {
        return "Teacher{" + "id=" + id + super.toString() + ", lessons=" + Arrays.toString(lessons) + '}';
    }    
    
    /**
     * Checks to see if {@code les} exists in the list of lessons
     * @param lessons array of lessons
     * @param les lesson to search for
     * @return {@code true} if {@code les} is found in {@code lessons}
     */
    private int contains(String[] lessons, String les) {
        for (int i = 0; i < index; i++) {
            String lesson = lessons[i];
            if (lesson != null && lesson.equalsIgnoreCase(les)) {
                return i;
            }
        }
        return -1;
    }

    /**
     * Remove index {@code indx} from {@code lessons}
     * @param indx index
     * @return {@code true} if the lesson was successfully removed.
     */
    private boolean remove(int indx) {
        if (indx < 0 || indx >= this.lessons.length) {
            return false;
        }
        String[] newLessons = new String[this.lessons.length - 1];
        // αντιγραφή από το 0 μέχρι το lessons[index-1]
        System.arraycopy(this.lessons, 0, newLessons, 0, indx);
        // αντιγραφή από lessons[index+1] μέχρι lessons[lessons.length-1]
        System.arraycopy(this.lessons, indx + 1, newLessons, indx, this.lessons.length - indx - 1);
        this.lessons = newLessons;
        index--;
        return true;
    }
}

package school;
import java.util.Arrays;
import java.util.Objects;
import school.validation.Validation;

/**
 * A classroom has a name, a size and contains students.
 */
public class ClassRoom {
    /** Empty classroom name. */
    private static final String NO_CLASSROOM = "--";
    /** Classroom's name. */ 
    private final String name;
    /** Classroom's size. */ 
    private final int size;
    /** Classrooms' students. */ 
    private Student[] students;
    /** Classroom's number of students. */ 
    private int index = 0;

    /**
     * Constructor.
     * 
     * @param name classroom's name
     * @param size classroom's size
     * @see school.validation.Validation#isClassRoomNameValid(java.lang.String) 
     * @see school.validation.Validation#isSizeValid(int)
     * @see school.validation.Validation#CLASSROOM_MAX_SIZE
     * @see NO_CLASSROOM
     */
    public ClassRoom(String name, int size) {
        this.name = Validation.isClassRoomNameValid(name) ? name : NO_CLASSROOM;
        this.size = Validation.isSizeValid(size) ? size : Validation.CLASSROOM_MAX_SIZE;
        this.students = new Student[size];
    }

    /**
     * Constructor. Default size.
     * 
     * @param name classroom's name. 
     * @see school.validation.Validation#CLASSROOM_MAX_SIZE
     */
    public ClassRoom(String name) {
        this(name, Validation.CLASSROOM_MAX_SIZE);
    }

    /**
     * @return classroom's name
     */
    public String getName() {
        return name;
    }

    /**
     * @return classroom's size
     */
    public int getSize() {
        return size;
    }

    /**
     * Add {@code student} to the class. 
     * @param student to add
     */
    public void addStudent(Student student) {
        if (student != null && index < size) {
            students[index++] = student;
            student.setClassRoom(this);
        }
    }

    /**
     * Remove student with {@code am} from this class.
     * @param am student's reg. number.
     */
    public void removeStudent(int am) {
        int indx = contains(students, am);
        if (indx != -1) {
            Student student = students[indx];
            if (remove(indx)) {
                student.setClassRoom(null);
            }
        }
    }

    /**
     * Remove {@code student} from this class.
     * 
     * @param student student to remove from this class
     */
    public void removeStudent(Student student) {
        if (student != null) {
            removeStudent(student.getAm());
            student.setClassRoom(null);
        }
    }

    /**
     * Empty this class.
     */
    public void removeAllStudents() {
        for (int i = 0; i < index; i++) {
            students[i].setClassRoom(null);
        }
        Arrays.fill(students, null);
        index = 0;
    }
    
    /**
     * Checks if the student is in this class.
     * @param am am of student to search for
     * @return {@code true} if the student with the given {@code am} exists in this class.
     */
    public boolean contains(int am) {
        return contains(this.students, am) >= 0;
    }
    
    /**
     * @return the students of this class. 
     */
    public Student[] getStudents() {
        return Arrays.copyOf(students, index);
    }       

    /**
     * Checks to see if {@code am} exists in the list of students
     * @param students array of students
     * @param am am to search for
     * @return {@code true} if {@code am} is found in {@code students}
     */
    private int contains(Student[] students, int am) {
        for (int i = 0; i < index; i++) {
            Student student = students[i];
            if (student != null && student.getAm() == am) {
                return i;
            }
        }
        return -1;
    }

    /**
     * Remove index {@code indx} from {@code students}
     * @param indx index
     * @return {@code true} if the student was successfully removed.
     */
    private boolean remove(int indx) {
        if (indx < 0 || indx > this.index) return false;
        Student[] newStudents = new Student[this.students.length - 1];
        // αντιγραφή από το 0 μέχρι το students[index-1]
        System.arraycopy(this.students, 0, newStudents, 0, indx);
        // αντιγραφή από students[index+1] μέχρι students[students.length-1]
        System.arraycopy(this.students, indx + 1, newStudents, indx, this.students.length - indx - 1);
        this.students = newStudents;
        index--;
        return true;
    }

    @Override
    public int hashCode() {
        int hash = 7;
        hash = 29 * hash + Objects.hashCode(this.name);
        return hash;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj == null) {
            return false;
    
        }
        if (getClass() != obj.getClass()) {
            return false;
        }
        final ClassRoom other = (ClassRoom) obj;
        return Objects.equals(this.name, other.name);
    }

    @Override
    public String toString() {
        return "ClassRoom{" + "name=" + name + ", size=" + size + ", numOfStudents=" + index + '}';
    }
}

Θα τροποποιήσουμε τις κλάσεις ClassRoom και Teacher. Τι δομή θα χρησιμοποιούσατε για να αποθηκεύσετε τους μαθητές στην κλάση ClassRoom; Επειδή δεν μας ενδιαφέρει η σειρά των μαθητών και δε θα θέλαμε να καταχωρήσουμε κατά λάθος τον ίδιο μαθητή δυο φορές στην ίδια τάξη, θα χρησιμοποιήσουμε τη δομή Set. Θα κάνουμε και άλλες αλλαγές όπως φαίνεται παρακάτω:

package school;
import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.Objects;
import java.util.Set;
import school.validation.Validation;

/**
 * A classroom has a name, a size and contains students.
 */
public class ClassRoom {
    /** Empty classroom name. */
    private static final String NO_CLASSROOM = "--";
    /** Classroom's name. */ 
    private final String name;
    /** Classroom's size. */ 
    private final int size;
    /** Classrooms' students. */ 
    private final Set<Student> students;

    /**
     * Constructor.
     * 
     * @param name classroom's name
     * @param size classroom's size
     * @see school.validation.Validation#isClassRoomNameValid(java.lang.String) 
     * @see school.validation.Validation#isSizeValid(int)
     * @see school.validation.Validation#CLASSROOM_MAX_SIZE
     * @see NO_CLASSROOM
     */
    public ClassRoom(String name, int size) {
        this.name = Validation.isClassRoomNameValid(name) ? name : NO_CLASSROOM;
        this.size = Validation.isSizeValid(size) ? size : Validation.CLASSROOM_MAX_SIZE;
        this.students = new HashSet<>(size);
    }

    /**
     * Constructor. Default size.
     * 
     * @param name classroom's name. 
     * @see school.validation.Validation#CLASSROOM_MAX_SIZE
     */
    public ClassRoom(String name) {
        this(name, Validation.CLASSROOM_MAX_SIZE);
    }

    /**
     * @return classroom's name
     */
    public String getName() {
        return name;
    }

    /**
     * @return classroom's size
     */
    public int getSize() {
        return size;
    }

    /**
     * Add {@code student} to the class. 
     * @param student to add
     */
    public void addStudent(Student student) {
        if (student != null && students.size() < size) {
            students.add(student);
            student.setClassRoom(this);
        }
    }

    /**
     * Remove student with {@code am} from this class.
     * @param am student's reg. number.
     * @return the removed student
     */
    public Student removeStudent(int am) {
        Student student = contains(am);
        if (removeStudent(student)) {
           student.setClassRoom(null);
        }
        return student;
    }

    /**
     * Remove {@code student} from this class.
     * 
     * @param student student to remove from this class
     * @return {@code true} if student was removed successfully
     */
    public boolean removeStudent(Student student) {
        boolean removed = false;
        if (student != null) {
            removed = students.remove(student);
            if (removed) {
                student.setClassRoom(null);
            }
        }
        return removed;
    }

    /**
     * Empty this class.
     */
    public void removeAllStudents() {
        for (Student student : students) {
            student.setClassRoom(null);
        }
        students.clear();
    }
    
    /**
     * Checks if the student is in this class.
     * @param am am of student to search for
     * @return {@code true} if the student with the given {@code am} exists in this class.
     */
    public Student contains(int am) {
        for (Student student : students) {
            if (student.getAm() == am) {
                return student;
            }
        }
        return null;
    }
    
    /**
     * @return the students of this class. 
     */
    public Collection<Student> getStudents() {
        return Collections.unmodifiableCollection(students);
    }

    @Override
    public int hashCode() {
        int hash = 7;
        hash = 29 * hash + Objects.hashCode(this.name);
        return hash;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj == null) {
            return false;
    
        }
        if (getClass() != obj.getClass()) {
            return false;
        }
        final ClassRoom other = (ClassRoom) obj;
        return Objects.equals(this.name, other.name);
    }

    @Override
    public String toString() {
        return "ClassRoom{" + "name=" + name + ", size=" + size + ", numOfStudents=" + students.size() + '}';
    }
}

Ξεφορτωθήκαμε την index, τις private contains(), remove() και απλοποιήσαμε άλλες μεθόδους.

Παρόμοια και στην Teacher:

package school;

import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.HashSet;
import java.util.Objects;
import java.util.Set;
import school.validation.Validation;

/**
 * A school teacher.
 */
public class Teacher extends Person {
    /** Max number of lessons a teacher can teach in the school. */
    private static final int MAX_LESSONS = 3;
    /** No ID number. */
    private String id = NONE;  // ΑΔΤ
    /** Lessons the teacher can teach. */
    private final Set<String> lessons;

    /**
     * Constructor.
     * 
     * @param id teacher's ID number
     * @param firstName teacher's first name
     * @param lastName teacher's last name
     * @param lessons a teacher can teach up to 3 lessons
     * @see MAX_LESSONS
     * @see school.validation.Validation#isIdValid(java.lang.String) 
     */
    public Teacher(String id, String firstName, String lastName, String... lessons) {
        super(firstName, lastName);
        if (Validation.isIdValid(id)) {
            this.id = id;
        }
        if (lessons != null && lessons.length > 0) { // αντιγράφουμε μόνο τα 3 πρώτα μαθήματα
            int length = lessons.length > MAX_LESSONS ? MAX_LESSONS : lessons.length;
            this.lessons = new HashSet<>(Arrays.asList(Arrays.copyOfRange(lessons, 0, length)));
        } else {
            this.lessons = new HashSet<>(MAX_LESSONS);
        }
    }

    /**
     * @return the teacher's ID number
     */
    public String getId() {
        return id;
    }

    /**
     * Set the teacher's id.
     * 
     * @param id the new ID number. It shouldn't be null.
     * @see school.validation.Validation#isIdValid(java.lang.String)
     */
    public void setId(String id) {
        this.id = Validation.isIdValid(id) ? id : NONE;
    }

    /**
     * Add a new lesson that this teacher teaches. If the number of lessons
     * that a teacher can teach is reached, the lesson is ignored.
     * @param lesson lesson to add
     */
    public void addLesson(String lesson) {
        if (lesson != null && lessons.size() < MAX_LESSONS) {
            lessons.add(lesson);
        }
    }
    /**
     * Remove the lesson from the lessons that this teacher teaches. If the 
     * lesson is not teached by this teacher, it is ignored.
     * @param lesson lesson to remove
     */
    public void removeLesson(String lesson) {
        if (lesson != null) {
            this.lessons.remove(lesson);
        }
    }
    
    /**
     * Checks if the teacher teaches this lesson.
     * @param les lesson to search for
     * @return {@code true} if the teacher teaches this lesson.
     */
    public boolean contains(String les) {
        return les == null ? false : this.lessons.contains(les);
    }
    
    /**
     * @return the lessons that this teacher teaches. 
     */
    public Collection<String> getLessons() {
        return Collections.unmodifiableCollection(this.lessons);
    }    

    @Override
    public int hashCode() {
        int hash = 3;
        hash = 59 * hash + Objects.hashCode(this.id);
        return hash;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj == null) {
            return false;
        }
        if (getClass() != obj.getClass()) {
            return false;
        }
        final Teacher other = (Teacher) obj;
        return Objects.equals(this.id, other.id);
    }

    @Override
    public String toString() {
        return "Teacher{" + "id=" + id + super.toString() + ", lessons=" + lessons + '}';
    }    

}

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