Lesson: Inheritance and Polymorphism

 1. 

package org.example3;

public class Parent {
    public String name;
    public String surname;
    public Integer age;

    public Parent() {
    }

    public Parent(String name) {
        this.name = name;
    }

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

    public Parent(String name, String surname, Integer age) {
        this.name = name;
        this.surname = surname;
        this.age = age;
    }
}
package org.example3;

public class Child extends Parent{
    public String hobby;

    public Child() {
        super(hobby);
    }
}

Burada problem ondan ibaretdir ki, Parent class yaranmamiw Child class yarana bilmez, ve ona gore de

biz hooby state-ni iwlede bilmirik. 


2. super keyword metodlarda:

package org.example3;

public class Parent {
    public String name;
    public String surname;
    public Integer age;

    public Parent() {
    }

    public Parent(String name) {
        this.name = name;
    }

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

    public Parent(String name, String surname, Integer age) {
        this.name = name;
        this.surname = surname;
        this.age = age;
    }

    public void method() {
        System.out.println("method in Parent");
    }
}
package org.example3;

public class Child extends Parent{
    public String hobby;

    public void foo() {
        super.method();
    }

    public void method() {
        System.out.println("method in Child");
    }
}
package org.example3;

public class Main {
    public static void main(String[] args) {
        Child child = new Child();
        child.method();
        child.foo();
    }
}

-- diger versiya

package org.example3;

public class Child extends Parent {
    public String hobby;

    public void foo() {
        method();
    }
}


-- 

package org.example3;

public class Main {
    public static void main(String[] args) {
        Child child = new Child();
        child.name = "Ali";
        child.surname = "Aliyev";
        child.age = 12;
        foo(child);
    }

    public static void foo(Parent parent) {
        System.out.println(parent.name);
        System.out.println(parent.surname);
        System.out.println(parent.age);
    }
}


-- instanceOf:

package org.example3;

public class Grandchild extends Child{
    public String toy;
}
package org.example3;

public class Main {
    public static void main(String[] args) {
        Grandchild grandchild = new Grandchild();
        System.out.println(grandchild instanceof Grandchild);
        System.out.println(grandchild instanceof Child);
        System.out.println(grandchild instanceof Parent);
    }

    public static void foo(Parent parent) {
        System.out.println(parent.name);
        System.out.println(parent.surname);
        System.out.println(parent.age);
    }
}


-- problem1:

package org.example3;

public class Child2 extends Parent{
    public boolean agression;
}
package org.example3;

public class Main {
    public static void main(String[] args) {
        Child2 child2 = new Child2();
        foo(child2);
    }

    public static void foo(Parent parent) {
        Child child = (Child) parent;
        System.out.println(child.hobby);
    }
}

-- solution:

package org.example3;

public class Main {
    public static void main(String[] args) {
        Child2 child2 = new Child2();
        foo(child2);
    }

    public static void foo(Parent parent) {
        if (parent instanceof Child) {
            Child child = (Child) parent;
            System.out.println(child.hobby);
        } else {
            Child2 child2 = (Child2) parent;
            System.out.println(child2.agression);
        }
    }
}


-- Using polymorphism in methods:

package org.example4;

public class Parent {
    public void sayHi() {
        System.out.println("Parent saying hi...");
    }
}
package org.example4;

public class Child1 extends Parent{
}
package org.example4;

public class Child2 extends Parent{
}
package org.example4;

public class Main {
    public static void main(String[] args) {
        Parent[] parents = {new Child1(), new Child2()};
        callAllParents(parents);
    }

    public static void callAllParents(Parent[] parents) {
        for (int i = 0; i < parents.length; i++) {
            Parent parent = parents[i];
            parent.sayHi();
        }
    }
}

--- Normal situation

package org.example4;

public class Parent {

    public int i = 0;
    public void sayHi() {
        System.out.println("Parent saying hi...");
    }
}
package org.example4;

public class Child1 extends Parent{

    public int i = 1;

    public void sayHi() {
        System.out.println("Child1 saying hi...");
    }
}
package org.example4;

public class Child2 extends Parent {

    public int i = 2;

    public void sayHi() {
        System.out.println("Child2 saying hi...");
    }
}
package org.example4;

public class Main {
    public static void main(String[] args) {
        Parent parent = new Parent();
        parent.sayHi();
        System.out.println(parent.i);

        Child1 child1 = new Child1();
        child1.sayHi();
        System.out.println(child1.i);

        Child2 child2 = new Child2();
        child2.sayHi();
        System.out.println(child2.i);
    }
}


-- Seems to be abnormal situation:

package org.example4;

public class Main {
    public static void main(String[] args) {
        Child1 child1 = new Child1();
        child1.sayHi();
        System.out.println(child1.i);

        Parent p = child1;
        p.sayHi();
        System.out.println(p.i);
    }
}

But it is pretty reasonable if we pay attention to reference, and its place in heap memory.

It is called override!


-- Another problem:

package org.example5;

public class A {

    public B foo() {
        System.out.println("foo in A");
        return new B();
    }
}
package org.example5;

public class B extends A {

    public A foo() {
        System.out.println("foo in B");
        return new A();
    }
}
package org.example5;

public class Main extends A{
    public static void main(String[] args) {
        A[] as = {new A(), new B()};
        method(as);
    }

    public static void method(A[] as) {
        for(int i = 0; i < as.length; i++) {
            A a = as[i];
            a.foo();
        }
    }
}


-- Interesting case:

package org.example6;

public class Father {

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

    public void method() {
        this.foo();
    }
}
package org.example6;

public class Son extends Father{

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

    public void fooSuper() {
        super.foo();
    }
}
package org.example6;

public class Main {
    public static void main(String[] args) {
        Father father = new Son();
        father.foo();
        father.method();
    }
}


-- Upcasting and Downcasting izahi:


------------------------------------------------------------------------------------------------------------------------------

                                                            Equals and HashCode

package org.example6;

public class Main {
    public static void main(String[] args) {
        Object o1 = new Object();
        Object o2 = new Object();
        System.out.println(o1 == o2);
        System.out.println(o1.equals(o2));
        
        String one = new String("test");
        String two = new String("test");

        System.out.println(one == two);
        System.out.println(one.equals(two));
        
        Object oOne = one;
        Object oTwo = two;
        System.out.println(one == two);
        System.out.println(one.equals(two));
    }
}


-----------------------------------------------------------------------------------------------------------------------------

package org.lesson11;

public class Employee {
    protected int no;
    protected String name;
    protected int year;
    protected String department;
    public static final int BASE_SALARY = 500;

    public Employee(int no, String name, int year, String department) {
        this.no = no;
        this.name = name;
        this.year = year;
        this.department = department;
    }

    public void work() {
        System.out.println("Employee is working...");
    }

    public double calculateSalary() {
        return year * BASE_SALARY;
    }

    public void printInfo() {
        System.out.println("\nNo: " + no);
        System.out.println("Name: " + name);
        System.out.println("Year: " + year);
        System.out.println("Department: " + department);
    }
}
package org.lesson11;

public class Manager extends Employee{
    protected String departmentManaged;
    public static final int MANAGEMENT_PAYMENT = 6000;

    public Manager(int no, String name, int year, String department, String departmentManaged) {
        super(no, name, year, department);
        this.departmentManaged = departmentManaged;
    }

    public void work() {
        System.out.println("Manager is working...");
        manage();
    }

    public void manage() {
        System.out.println("Manager manages department: " + departmentManaged);
    }

    public double calculateSalary() {
        return super.calculateSalary() + MANAGEMENT_PAYMENT;
    }

    public void printInfo() {
        super.printInfo();
        System.out.println("Managing Department: " + departmentManaged);
    }
}
package org.lesson11;

public class Director extends Manager{
    protected double bonus;

    public Director(int no, String name, int year, String department, String departmentManaged, double bonus) {
        super(no, name, year, department, departmentManaged);
        this.bonus = bonus;
    }

    public void work() {
        System.out.println("Director is working...");
        manage();
    }

    public void manage() {
        System.out.println("Director manages whole company");
        makeStrategicPlan();
    }

    public void makeStrategicPlan() {
        System.out.println("Directors makes a strategic plan for the company");
    }

    public double calculateSalary() {
        return super.calculateSalary() + bonus;
    }
}
package org.lesson11;

public class Main {
    public static void main(String[] args) {
        Employee e1 = new Employee(1, "Ali", 8, "Production");
        e1.printInfo();
        System.out.println("Salary: " + e1.calculateSalary());
        e1.work();

        System.out.println("--------------------------------------------------------");

        Manager m1 = new Manager(2, "Vali", 3, "Production", "Production");
        m1.printInfo();
        System.out.println("Salary: " + m1.calculateSalary());
        m1.work();
        m1.manage();

        System.out.println("---------------------------------------------------------");

        Director d1 = new Director(4, "Test", 28, "Management", "Management", 3000);
        d1.printInfo();
        System.out.println("Salary: " + d1.calculateSalary());
        d1.work();
        d1.makeStrategicPlan();
    }
}

-----------

package org.lesson11;

public class HR {

    public Employee getAnEmployee() {
        return new Employee(1, "Ali", 8, "Production");
    }
}
package org.lesson11;

public class HRForManagers extends HR{

    public Manager getAnEmployee() {
        return new Manager(2, "Vali", 3, "Production", "Production");
    }
}


*** Covariant return type ***

package org.lesson11;

public class HR {

    public Employee getAnEmployee() {
        return new Employee(1, "Ali", 8, "Production");
    }
}
package org.lesson11;

public class HRForManagers extends HR{

    public Manager getAnEmployee() {
        return new Manager(2, "Vali", 3, "Production", "Production");
    }
}


------------------------------------------------------------------------------------------------------------------------------

toString() metodu

Mes: Car car = new Car(...);

System.out.println(car);

System.out.println(car.toString());

Bu iki method ayni iwi gorur.




















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