(JAVA) Bài 4: Khai báo và nhập trị cho biến

package sudungbien;

import java.util.Scanner; // KHAI BAO THU VIEN NHAP LIEU

public class SuDungBien {

    public static void main(String[] args) {
       
    final String dongke    ="-----------------------------------";
    final String tieude = "CHUONG TRINH KHAI BAO-NHAP TRI CHO BIEN";

    Scanner nhap = new Scanner(System.in);
   
    System.out.println(tieude);
    System.out.println(dongke);
    System.out.println("1. HINH VUONG");
    int canh;
    System.out.print("Nhap vao so da canh hinh vuong: ");
    canh=nhap.nextInt();

    int cvV=canh*4;
    int dtV=canh*canh;
    System.out.println("Chu vi hinh vuong: "+cvV);
    System.out.println("Dien tich hinh vuong: "+dtV);
    System.out.println(dongke);
    System.out.println("2. HINH CHU NHAT");

    float dai,rong,cvCN,dtCN;
    System.out.print("Nhap chieu dai hinh chu nhat: ");
    dai=nhap.nextFloat();
     
    System.out.print("Nhap chieu rong hinh chu nhat: ");
    rong=nhap.nextFloat();

    cvCN=(dai+rong)*2;
    dtCN=dai*rong;
    System.out.format("Chu vi hinh chu nhat: %.2f%n",cvCN);
    System.out.format("Dien tich hinh chu nhat: %.2f%n",dtCN);
    System.out.println(dongke);

    System.out.println("3. HINH TAM GIAC");
    double a,b,c,cvTG,dtTG;
    System.out.println("Nhap vao 3 canh tam giac: ");
    System.out.print("Canh thu 1: ");
    a=nhap.nextDouble();
    System.out.print("Canh thu 2: ");
    b=nhap.nextDouble();
    System.out.print("Canh thu 3: ");
    c=nhap.nextDouble();
    cvTG=a+b+c;
    double p=cvTG/2;
    dtTG=Math.sqrt(p*(p-a)*(p-b)*(p-c));
    System.out.format("Dien tich tam giac: %.2f%n",dtTG);

    System.out.println(dongke);

    System.out.println("4. HINH TRON");
    final double PI=3.14159f;
    double dk,cvHT,dtHT;
    System.out.print("Nhap vao duong kinh hinh tron: ");
    dk=nhap.nextFloat();
    cvHT=dk*PI;
    dtHT=Math. pow (dk/2,2)*PI;
    System.out.format("Chu vi hinh tron: %.3f%n",cvHT);
    System.out.format("Dien tich hinh tron: %.3f%n",dtHT);

    System.out.println(dongke); 
       }
}