How to make a program calculate the area of several objects separately using the values given by the user (scanner)

Question

I am new here and new in programming, I believe that the best way to establish the concepts and learn is in practice.

So I tried to do some basic programming on Eclipse (also use Intellij) and at first it worked, I wanted to use the Scanner of java I couldn’t get it right and I’m in it on time...

I believe it’s quite simple, the program consists of calculate to object area (triangle and trapezoid I inserted, just to test) with the value given by the user for example:

The formula of the area of a triangle is A = (b*h)/2 being b = base and h = altura.

The values of b and h who will give is the user in the console and so the program will calculate and return the value of the area (A) of settlement with the chosen geometric object.

But the problem is not in the resolution of the account, this part is all right.

The problem is time to make the user choose which geometric object (triangle or trapezoid) he wants to know the area for the program to calculate and execute only the block of code of that object, ignoring the other since it was not chosen.

My program asks for the value of both and regardless of what I do it does not execute only one of them, can be several mistakes I made and as a layman in this subject I ask for help to solve, either by a totally new code or reusing mine.

Follow the code below:

package Course;

import java.util.Scanner;

public class Utilizandoscanner1 {

public static void main(String[] args) {
    /*Descubra a área do que o usuário passar
     * Trapézio: A = ((B + b)/2) * h
     * B = Base maior, b = base menor, h = altura
     * 
     * Triângulo: A = (B*h)/2
     * B = Base, h = altura
     */


    System.out.println("Bem-vindo ao calculador de área!");
    System.out.println("Informe qual objeto quer calcular: ");

    Scanner input = new Scanner(System.in);

    boolean trapézio = true, triângulo = true;

    if(trapézio){
        Double B,b,h,A;
        //coletando os valores do usuário
        System.out.println("Informe o valor de B = base maior: ");
        B = input.nextDouble();
        System.out.println("Informe o valor de b = base menor: ");
        b = input.nextDouble();
        System.out.println("Informe o valor de h = altura");
        h = input.nextDouble();
        //calculando
        A = ((B + b)/2)*h;
        System.out.println("O valor dado é B: "+B+" b: "+b+" h: "+h);
        System.out.println("A área do trapézio é: "+A);
        input.close();
    }
    if(triângulo){
        Double B,h,A;
        //coletando valores do usuário
        System.out.println("Informe o valor de B = base: ");
        B = input.nextDouble();
        System.out.println("Informe o valor de h = altura: ");
        h = input.nextDouble();
        //calculando
        A = (B*h)/2;
        System.out.println("O valor dado é B: "+B+" h: "+h);
        System.out.println("A área do triângulo é: "+A);
        input.close();
    }   


}

}

Answer 1

    public static void main(String[] args) {
        /*Descubra a área do que o usuário passar
         * Trapézio: A = ((B + b)/2) * h
         * B = Base maior, b = base menor, h = altura
         *
         * Triângulo: A = (B*h)/2
         * B = Base, h = altura
         */

        boolean trapezio = false, triangulo = false;

        System.out.println("Bem-vindo ao calculador de área!");
        System.out.println("Informe qual objeto quer calcular: ");

        Scanner input = new Scanner(System.in);

        String escolhaDoUsuario = new String();
        escolhaDoUsuario = input.next();

        if(escolhaDoUsuario.equals("trapezio")) {
            trapezio = true;
        } else if(escolhaDoUsuario.equals("triangulo")) {
            triangulo = true;
        }

        if(trapezio){
            Double B,b,h,A;
            //coletando os valores do usuário
            System.out.println("Informe o valor de B = base maior: ");
            B = input.nextDouble();
            System.out.println("Informe o valor de b = base menor: ");
            b = input.nextDouble();
            System.out.println("Informe o valor de h = altura");
            h = input.nextDouble();
            //calculando
            A = ((B + b)/2)*h;
            System.out.println("O valor dado é B: "+B+" b: "+b+" h: "+h);
            System.out.println("A área do trapézio é: "+A);
            input.close();
        }
        if(triangulo){
            Double B,h,A;
            //coletando valores do usuário
            System.out.println("Informe o valor de B = base: ");
            B = input.nextDouble();
            System.out.println("Informe o valor de h = altura: ");
            h = input.nextDouble();
            //calculando
            A = (B*h)/2;
            System.out.println("O valor dado é B: "+B+" h: "+h);
            System.out.println("A área do triângulo é: "+A);
            input.close();
        }
    }

This is a very naive implementation, but the idea was just to finish it using the logic you developed. A "version 2.0" could have several improvements:

• And if the user type "TRIANGLE"?
• Use methods instead of code blocks.
• What if the user types a geometric shape not foreseen by the program? What if he does not type anything?
• Ask the user if he wants to calculate another figure instead of the program simply exiting after running once.
• Use only a structure of if.
• Eliminate the booleans.

The list could be even bigger. It remains for you to study repetition structures like while, flow structures such as the switch, investigate the method equals() I used etc.