Java Basic- OOP - Interface - Hình chữ nhật trong java

#HinhChuNhat.java

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package bt995;

/**
 *
 * @author Diep.Tran
 */
public class HinhChuNhat implements HCNInterface{
    double chieudai, chieurong;
    
    @Override
    public double dientichHCN() {
        return chieudai * chieurong;
    }

    @Override
    public double getChieuDai() {
        return chieudai;
    }

    @Override
    public double getChieuRong() {
        return chieurong;
    }

    @Override
    public void setDaiRong(double cd, double cr) {
        chieudai = cd;
        this.chieurong = cr;
    }
    
}

#HCNTest.java

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package bt995;

import java.util.Collections;
import java.util.Scanner;

/**
 *
 * @author Diep.Tran
 */
public class HCNTest {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        
        System.out.println("Nhap so HCN = ");
        int n = Integer.parseInt(scan.nextLine());
        
        HinhChuNhat[] hcnList = new HinhChuNhat[n];
        
        //Nhap thong tin N HCN
        double cd, cr;
        for (int i = 0; i < n; i++) {
            System.out.println("Nhap chieu dai: ");
            cd = Double.parseDouble(scan.nextLine());
            System.out.println("Nhap chieu rong: ");
            cr = Double.parseDouble(scan.nextLine());
//            HinhChuNhat hcn = new HinhChuNhat();
//            hcn.setDaiRong(cd, cr);
//            hcnList[i] = hcn;
            hcnList[i] = new HinhChuNhat();
            hcnList[i].setDaiRong(cd, cr);
        }
        
        
        System.out.println("Thong tin N HCN");
        for (HinhChuNhat hcn : hcnList) {
            System.out.println("Chieu dai: " + hcn.getChieuDai() + 
                    ", chieu rong: " + hcn.getChieuRong() + 
                    ", dien tich: " + hcn.dientichHCN()
            );
        }
        
        //Tim HCN co dien max
        int maxIndex = 0;//Vi tri phan tu co dien tich max
        double maxDientich = hcnList[maxIndex].dientichHCN();
        for (int i = 1; i < hcnList.length; i++) {
            double dt = hcnList[i].dientichHCN();
            if(maxDientich < dt) {
                maxIndex = i;
                maxDientich = dt;
            }
        }
        
        System.out.println("Thong tin HCN max: ");
        HinhChuNhat hcn = hcnList[maxIndex];
        System.out.println("Chieu dai: " + hcn.getChieuDai() + 
                    ", chieu rong: " + hcn.getChieuRong() + 
                    ", dien tich: " + hcn.dientichHCN()
            );
    }
}

#HCNInterface.java

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package bt995;

/**
 *
 * @author Diep.Tran
 */
public interface HCNInterface {
    double dientichHCN();
    
    double getChieuDai();
    double getChieuRong();
    
    void setDaiRong(double cd, double cr);
}