OOP_1

package practice1;

/**
 *
 * @author valik888
 */
import java.io.*;
import java.util.*;

public class mainClass {
    public static void main(String[] args) throws IOException {
      System.out.println("Введите сторону квадрата: ");
      double a, answer;
      BufferedReader bf = new BufferedReader(new InputStreamReader(System.in));
      Scanner sc = new Scanner(System.in);
      /* double a = Double.parseDouble(sc.nextDouble()); */
      String str = bf.readLine();
      a = Double.parseDouble(str);
      if(a <=0 ){
          System.out.println("Ошибка ввода!");
      } else {
          answer = a * a;
          System.out.println("Площадь квадрата равна: " + answer);
      }

    }
}