- Tính chất trong lập trình hướng đối tượng (OOP)
	- Tính chất đóng gói => OK
	- Tính kế thừa => OK
		- override
		- overloading
	- Tính đa hình
	- Tính trừu tượng
- Interface
======================================================
Mini Project:
Viết chương trình quản lý công dan + sinh viên + xe cộ + động vật trong thành phố.

Yêu cầu:
1) Xây dựng lớp đối tượng công dân + sinh viên
- Citizen:
	- Thuộc tính: Tên, tuổi, địa chỉ, cmtnd
	- Hành động:
		- input & display -> Nhập & hiển thị thông tin
		- running
- Student
	- Thuộc tính: Tên, tuổi, địa chỉ, cmtnd, rollno, email
	- Hành động:
		- input & display -> Nhập & hiển thị thông tin
		- running
		- learning

2) Triển khai dự án

#Test.java

/*
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package lesson04;

/**
 *
 * @author Diep.Tran
 */
public class Test {
    public static void main(String[] args) {
        Dog dog = new Dog();
        dog.showSound();
        
        Cat cat = new Cat();
        cat.showSound();
        
        //Xay dung chuong trinh -> Su dung 1 list quan ly toan bo doi tuong Car, Citizen, Student, Dog, Cat...
        //Quan ly hanh dong running() cho class object nay.
        //Giai phap la gi???
    }
}

#Student.java

/*
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 */
package lesson04;

import java.util.Scanner;

/**
 * Student: Child class -> lop con.
 * @author Diep.Tran
 */
public class Student extends Citizen{
    String rollno, email;

    public Student() {
    }

    public Student(String rollno, String email, String fullname, String address, String cmtnd, int age) {
        super(fullname, address, cmtnd, age);
        this.rollno = rollno;
        this.email = email;
    }

    public String getRollno() {
        return rollno;
    }

    public void setRollno(String rollno) {
        this.rollno = rollno;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }
    
    @Override
    public void input() {
        super.input();
        
        Scanner scan = new Scanner(System.in);
        
        System.out.println("Nhap rollno: ");
        rollno = scan.nextLine();
        
        System.out.println("Nhap email: ");
        email = scan.nextLine();
    }
    
    @Override
    public void display() {
        super.display();
        System.out.printf(", rollno: %s, email: %s\n", rollno, email);
    }
    
    public void learning() {
        System.out.println(fullname + " dang hoc bai!!!");
    }
    
    public void learning(String msg) {
        System.out.println(fullname + " dang hoc bai!!! -> " + msg);
    }
    
    public void learning(String msg, String msg2) {
        System.out.println(fullname + " dang hoc bai!!! -> " + msg + " -> " + msg2);
    }
}

#Main.java

/*
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package lesson04;

import java.util.ArrayList;

/**
 *
 * @author Diep.Tran
 */
public class Main {
    public static void main(String[] args) {
//        Student std = new Student();
//        std.input();
//        
//        std.display();
//        std.learning();
//        
//        std.learning("12345");
        
        //Tinh chat da hinh
//        Citizen citizen = new Citizen();
//        citizen.input();
//        citizen.display();

//        Citizen c = new Student();//Goi la tinh chat da hinh.
//        c.input();
//        c.display();
//        
//        if(c instanceof Student) {
//            ((Student) c).learning();
//        }
        
        //Ung dung trong lap trinh su dung tinh chat da hinh
        ArrayList<Citizen> list = new ArrayList<>();
//        ArrayList<Student> list2 = new ArrayList<>();
        
        //Quan ly nhap & hien thong tin du lieu cua Citizen va Student
        //Cach thong thuong -> su dung -> 2 Array de quan ly du lieu cua Citizen va Student
        //Co cach khac -> su dung chi 1 Array de quan ly ca Citizen & Student hay ko
        Citizen ci = new Citizen();
        list.add(ci);
        
        ci = new Student();
        list.add(ci);
        
        for (Citizen citizen : list) {
            citizen.input();
        }
        
        for (Citizen citizen : list) {
            citizen.display();
        }
    }
}

#Dog.java

/*
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 */
package lesson04;

/**
 *
 * @author Diep.Tran
 */
public class Dog extends Animal{

    @Override
    public void showSound() {
        System.out.println("Go .. go ..");
    }
    
}

#Citizen.java

/*
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package lesson04;

import java.util.Scanner;

/**
 * Citizen -> parent class & lop cha.
 * @author Diep.Tran
 */
public class Citizen {
    String fullname, address, cmtnd;
    int age;

    public Citizen() {
    }

    public Citizen(String fullname, String address, String cmtnd, int age) {
        this.fullname = fullname;
        this.address = address;
        this.cmtnd = cmtnd;
        this.age = age;
    }

    public String getFullname() {
        return fullname;
    }

    public void setFullname(String fullname) {
        this.fullname = fullname;
    }

    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public String getCmtnd() {
        return cmtnd;
    }

    public void setCmtnd(String cmtnd) {
        this.cmtnd = cmtnd;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        if(age >= 0) {
            this.age = age;
        } else {
            System.out.println("Yeu cau age >= 0");
        }
    }
    
    public void input() {
        Scanner scan = new Scanner(System.in);
        
        System.out.println("Nhap ten: ");
        fullname = scan.nextLine();
        
        System.out.println("Nhap dia chi: ");
        address = scan.nextLine();
        
        System.out.println("Nhap CMTND: ");
        cmtnd = scan.nextLine();
        
        System.out.println("Nhap tuoi: ");
        setAge(Integer.parseInt(scan.nextLine()));
    }
    
    public void display() {
        System.out.printf("\nTen: %s, age: %d, dia chi: %s, cmtnd: %s", fullname, age, address, cmtnd);
    }
    
    public void running() {
        System.out.println("Citizen is running");
    }
}

#Cat.java

/*
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 */
package lesson04;

/**
 *
 * @author Diep.Tran
 */
public class Cat extends Animal{

    @Override
    public void showSound() {
        System.out.println("Meo .. meo ..");
    }
    
}

#Car.java

/*
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package lesson04;

/**
 *
 * @author Diep.Tran
 */
public class Car {
    public void running() {
        System.out.println("Car is running ...");
    }
}

#Animal.java

/*
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 */
package lesson04;

/**
 *
 * @author Diep.Tran
 */
public abstract class Animal {
    String name, color;

    public Animal() {
    }

    public Animal(String name, String color) {
        this.name = name;
        this.color = color;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getColor() {
        return color;
    }

    public void setColor(String color) {
        this.color = color;
    }
    
    public void input() {
        System.out.println("Nhap thong tin Animal");
    }
    
    public void display() {
        System.out.println("Hien thi thong tin Animal");
    }
    
    public abstract void showSound();
    
    public void running() {
        System.out.println("Animal running ...");
    }
}