Java Basic- OOP - Chu vi và diện hình hình tròn & hình chữ nhật

#Circle.java

/*
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 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package bt985;

import java.util.Scanner;

/**
 *
 * @author std
 */
public class Circle {
    float r;

    public Circle() {
    }

    public Circle(float r) {
        this.r = r;
    }
    
    public void input() {
        Scanner scan = new Scanner(System.in);
        
        System.out.println("Nhap ban kinh: ");
        r = Float.parseFloat(scan.nextLine());
    }
    
    public double tinhChuVi() {
        return 2 * Math.PI * r;
    }
    
    public double tinhDienTich() {
        return Math.PI * r * r;
    }
}

#HinhChuNhat.java

/*
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 * To change this template file, choose Tools | Templates
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 */
package bt985;

import java.util.Scanner;

/**
 *
 * @author std
 */
public class HinhChuNhat {
    double width, height;

    public HinhChuNhat() {
    }

    public HinhChuNhat(double width, double height) {
        this.width = width;
        this.height = height;
    }
    
    public void input() {
        Scanner scan = new Scanner(System.in);
        
        System.out.println("Nhap chieu dai: ");
        width = Double.parseDouble(scan.nextLine());
        System.out.println("Nhap chieu cao: ");
        height = Double.parseDouble(scan.nextLine());
    }
    
    public double tinhChuVi() {
        return (width + height) * 2;
    }
    
    public double  tinhDienTich() {
        return width * height;
    }
}

#Main.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 bt985;

import java.util.Scanner;

/**
 *
 * @author std
 */
public class Main {
    public static void main(String[] args) {
        Circle circle = new Circle();
        HinhChuNhat hcn = new HinhChuNhat();
        
        Scanner scan = new Scanner(System.in);
        int choose;
        
        do {
            showMenu();
            choose = Integer.parseInt(scan.nextLine());
            
            switch(choose) {
                case 1:
                    circle.input();
                    break;
                case 2:
                    System.out.println("Chu vi hinh tron: " + circle.tinhChuVi());
                    break;
                case 3:
                    System.out.println("Dien tich hinh tron: " + circle.tinhDienTich());
                    break;
                case 4:
                    hcn.input();
                    break;
                case 5:
                    System.out.println("Chu vi hcn: " + hcn.tinhChuVi());
                    break;
                case 6:
                    System.out.println("Dien tich hcn: " + hcn.tinhDienTich());
                    break;
                case 7:
                    System.out.println("Thoat!!!");
                    break;
            }
        } while(choose != 7);
    }
    
    static void showMenu() {
        System.out.println("1. Nhap thong tin hinh tron");
        System.out.println("2. Chu vi");
        System.out.println("3. Dien tich");
        System.out.println("4. Nhap thong tin HCN");
        System.out.println("5. Chu vi");
        System.out.println("6. Dien tich");
        System.out.println("7. Thoat");
        System.out.println("Chon: ");
    }
}