SE_21_Lesson_10: Encapsulation, Inheritance

-> Encapsulation:

Problem1:

package org.example;

public class Rectangle {
    public double width;
    public double length;
}

package org.example;

public class Main {
    public static void main(String[] args) throws Exception {
        Rectangle r1 = new Rectangle();
        r1.length = 5;
        r1.width = 3;

        Rectangle r2 = new Rectangle();
        r2.length = 7;
        r2.width = 2;
    }

} 

Buradaki problem ondan ibaretdir ki, Rectangle klasinin icindeki field adi deyishilse butun yaratdigimiz obyektlerde de deyishiklikler aparmaliyiq.

Solution:

package org.example;

public class Rectangle {
    private double width;
    private double length;

    public double getWidth() {
        return width;
    }

    public void setWidth(double width) {
        this.width = width;
    }

    public double getLength() {
        return length;
    }

    public void setLength(double length) {
        this.length = length;
    }
}

package org.example;

public class Main {
    public static void main(String[] args) throws Exception {
        Rectangle r1 = new Rectangle();
        r1.setLength(5);
        r1.setWidth(3);

        Rectangle r2 = new Rectangle();
        r2.setLength(7);
        r2.setWidth(2);
    }
}

Adi deyishse bele biz sadece klasin icinde bir nece yerde deyishiklikler aparacayiq.

Problem 2:

package org.example;

public class Main {
    public static void main(String[] args) throws Exception {
        Rectangle r1 = new Rectangle();
        r1.length = -5;
        r1.width = 3;
    }
}

Burada biz menfi deyer menimsetdik, bu ise yol verilmezdir.

Solution:

package org.example.Lesson10;

public class Rectangle {
    private double width;
    private double length;

    public double getWidth() {
        return width;
    }

    public void setWidth(double width) {
        if (width < 0) {
            throw new RuntimeException("Menfi deyer olmaz");
        }
        this.width = width;
    }

    public double getLength() {
        return this.length;
    }

    public void setLength(double length) {
        if (length < 0) {
            throw new RuntimeException("Menfi deyer olmaz");
        }
        this.length = length;
    }
}

-> Inheritance:

package org.example;

public class Person {
    public String name;
    public String surname;
}

package org.example;

public class Student {
    public String name;
    public String surname;
}

package org.example;

public class Teacher {
    public String name;
    public String surname;
}

Burada gorduyumuz kimi kod tekrarlanir. 

package org.example;

public class Person {
    public String name;
    public String surname;
}

package org.example;

public class Student extends Person{
    public String studentCard;
}

package org.example;

public class Teacher extends Person{
    public String jobTitle;
}

Burada Student is a Person ve Teacher is a Person. Buna Is a relationship deyilir.

Has a relationship ise obyekti ozunde saxladiqda deyilir.

-> Super class-da constructor ishletdikde lakin child class-da ishletmedikde ne olur?

package org.example;

public class Person {
    public String name;
    public String surname;

    public Person(String name, String surname) {
        this.name = name;
        this.surname = surname;
    }
}

Sebeb ondadir ki, child klaslarin konstructorlarinin birinci setrinde default shekilde super() keyword var. Yeni extend elediyim klasin parametrsiz constructor-unu cagir, lakin super klasda parametrsiz constructor olmadigi ucun xeta aliriq.

-> this ve super keywordlerini bir arada ishletmek

package org.example;

public class Student extends Person{
    public String studentCard;

    public Student(String name, String surname, String studentCard) {
        this(name, surname);
        this.studentCard = studentCard;
    }

    public Student(String name, String surname) {
        super(name, surname);
    }
}

-> Super class yaranmamish Subclass-daki fieldlari ishlede bilmerik eks halda xeta aliraq

package org.example;

public class Teacher extends Person{
    public String jobTitle;

    public Teacher(String name, String surname) {
        super(name, surname);
    }

    public Teacher() {
        super(jobTitle);
    }
}

-> Hem base hem subclass-da eyni signature-i metodlar olduqda, super keywordunu metodda ishletmek

package org.example;

public class Person {
    public String name;
    public String surname;

    public Person(String name, String surname) {
        this.name = name;
        this.surname = surname;
    }

    public void foo() {
        System.out.println("foo in Person");
    }
}

package az.main;

public class Student extends Person {

    public String studentCard;

    public Student(String name, String surname, String studentCard) {
        super(name, surname);
        this.studentCard = studentCard;
    }

    public void foo() {
        System.out.println("foo in Student");
    }

    public void foo2() {
        super.foo();
        System.out.println("foo2 in Student");
    }

}

-> Super classdaki metodu subclassda this keywordu ile cagirmaq. (Bu zaman hidden shekilde sanki subclass-da olur)

package org.example.lesson_13;

public class A {
    public void methodInA() {
        System.out.println("You called methodInA in class A");
    }
}

package org.example.lesson_13;

public class B extends A{
    public void foo() {
        this.methodInA();
    }
}