Check string value

Question

I wanted you to check if the entered value is vegetarian, and if it is, print on the user’s screen is vegetarian as follows the code, but when I type vegetarians or anything else it warns that it is not.

import java.util.Scanner;
public class Alimentos {
    public static void main(String args[]){
        Scanner in = new Scanner(System.in);
        System.out.println("\nDigite o Alimento (Vegetariano, Peixe, Frango ou Carne): ");
        String alimento = in.nextLine();
        if(alimento == "Vegetarianos"){
        System.out.println("É Vegetariano");
    } else {
        System.out.println("nao é vegetariano");
    }
    }
}

Answer 1

The code has some problems. You are asking to type in the singular and comparing with the plural. And worse, it has to be with the first letter capitalized. Besides this you are not comparing two contents string but two references to strings that will obviously always be different:

import java.util.Scanner;

class Main {
    public static void main(String args[]){
        Scanner in = new Scanner(System.in);
        System.out.println("\nDigite o Alimento (Vegetariano, Peixe, Frango ou Carne): ");
        String alimento = in.nextLine();
        System.out.println(alimento.equals("Vegetariano") ? "É Vegetariano" : "nao é vegetariano");
    }
}

Behold working in the ideone. And in the repl it.. Also put on the Github for future reference.

The solutions:

• Use equals() to compare the content and not the reference. The operator == only compares if both refer to the same memory location, which is impossible in this case.

• Optionally you can make the string all to lower case before comparing to avoid slips in typing. The more normalized the text is, the easier it is to compare. For this it is possible to use the method toLowerCase() before comparing the content, or equalsIgnoreCase(), so kill both at once. So:

    alimento.toLowerCase().equals("vegetariano") // OU
    alimento.equalsIgnoreCase("Vegetariano")
  

• Optionally compare with everything in lowercase and not have the discrepancy of uppercase V and S at the end. If it is written in a specific way, it should always be typed that way. If it won’t normalize, then you should compare it exactly to the text you ask to type. If the V is capitalized, it should be in both places, if it is in the singular, it should be in both places.

• Ideally it should have an easier way of data entry to check and avoid errors. Asking someone to type a text to make a decision is asking for an error to happen. In these cases, a menu of options is used and the user enters a number, which is easier to compare.

Answer 2

I imagine that it is a school exercise or something like, after all, present options for user choice textual way is not usually ideal for practical use.

As the question problem has already been solved by @Maniero, it follows by joke (by exaggeration factor) an answer based on distance from Levenshtein, who will find things with little differences of spelling:

import java.util.*;
import java.lang.*;
import java.io.*;

class Alimentos {

    //http://rosettacode.org/wiki/Levenshtein_distance#Java
    public static int distance(String a, String b) {
        a = a.toLowerCase();
        b = b.toLowerCase();
        int [] costs = new int [b.length() + 1];
        for (int j = 0; j < costs.length; j++)
            costs[j] = j;
        for (int i = 1; i <= a.length(); i++) {
            costs[0] = i;
            int nw = i - 1;
            for (int j = 1; j <= b.length(); j++) {
                int cj = Math.min(
                    1 + Math.min(costs[j], costs[j - 1]),
                    a.charAt(i - 1) == b.charAt(j - 1) ? nw : nw + 1
                );
                nw = costs[j];
                costs[j] = cj;
            }
        }
        return costs[b.length()];
    }

    public static void main(String args[]){
        String[] alimentos = new String[4];
        alimentos[0] = "Vegetariano";
        alimentos[1] = "Peixe";
        alimentos[2] = "Frango";
        alimentos[3] = "Carne";
        String alimento;
        String resultado;
        int distancia;
        int prevDistancia;

        Scanner in = new Scanner(System.in);
        System.out.println("Digite o Alimento (Vegetariano, Peixe, Frango ou Carne): ");
        while ( in.hasNext() ) {
            alimento = in.nextLine();
            prevDistancia = 99999; // Valor maior do que qq distancia possivel aqui
            resultado = "";
            for ( String item : alimentos ) {
                distancia = distance( item, alimento );
                if ( prevDistancia > distancia ) {
                    prevDistancia = distancia;
                    resultado = item;
                }
            }
            System.out.println("Alimento: "+resultado );
        }
    }
}

Taking advantage, I modified the code to accept several entries then, until the user leaves the line blank, and in the output appear the four options, not just Vegetarian.

Example entries, purposely spelled differently from code:

Framgo
Pexe
Vegetais
Carnes

Results:

Digite o Alimento (Vegetariano, Peixe, Frango ou Carne): 
Alimento: Frango
Alimento: Peixe
Alimento: Vegetariano
Alimento: Carne

See working on IDEONE.