Encapsulation and Get and Set methods

Question

I am continuing my studies in object-oriented Java programming.

I am currently studying encapsulation and methods get and set and I came across the following exercise:

Encapsulate the value attribute of the Boleto class.

This attribute must not be set directly. The class user informs the value and the student. If the student is approved a 10% discount is granted on the amount of the ticket and the get method must display the amount with the discount granted.

And I created this code:

Pupil Class:

package Academico;

public class Aluno {

    public String nome;
    private String matricula;
    private String curso;
    protected Disciplina disciplina[];

}

Classe Disciplina:

package Academico;

public class Disciplina {

    String nome;
    double nota1, nota2, nota3, nota4;
   
}

Boleto class:

package Financeiro;

import Academico.*;

public class Boleto {

    private Aluno aluno;
    private String referencia;
    private double valor;
    
    public Boleto(Aluno aluno, String referencia, double valor){
        this.aluno = aluno;
        this.referencia = referencia;
        this.valor = valor;
    }
    
    public double desconto() {
        disciplina = new Disciplina[3];
        if(disciplina == true){
            this.valor = this.valor-(this.valor*0.1);
            return this.valor;
        }
    }
    
    public double getValorDesconto() {
        return this.valor;
    }

}

There is some error in code construction, encapsulation and methods Get and Set?

Answer 1

The question was edited, I made based on the original code posted

The exercise already seems to be well defined. So it is even difficult to say what is right. Without more accurate information you can’t say or help do right, you can’t say what’s right.

Not to be unanswered I will give a slight improvement and ask questions:

package Financeiro;

import Academico.Disciplina;

public class Boleto {
    private Aluno aluno;
    private String referencia; //o exercício não fala disto
    private double valor; //seria melhor usar um BigDecimal, mas para exercício ok

    public Boleto(Aluno aluno, String referencia, double valor){
        this.aluno = aluno;
        this.referencia = referencia;
        this.valor = valor;
    }

    public Aluno getAluno() { return aluno; }

    public String getReferencia() { return referencia; }

    public double getValor() { return valor; }

    public double desconto() { //isto faz e retorna o desconto, o nome não é bom
        disciplina = new Disciplina[3]; //isto não parece fazer o menor sentido,nem compila
        if (disciplina) { //onde está a verificação de aprovação?
            valor -=  valor * 0.1;
            return valor;
        }
    }

    public double getValorDesconto() { //qual o intuito disto? O requisito não pede
        return valor; //isto parece estar errado se o método faz sentido existir
    }
}

I put in the Github for future reference.

Possibly lacking methods set, but I don’t know if I should do this. The fact that I say the attribute should not be setate directly is that it should not be public and, in theory, can be setate indirectly through a method setXXX().

What’s to stop calling the discount several times and even reset the value? I know for an exercise this shouldn’t be very important, but it’s something to think about.

I think the discount calculation should be done in the builder and there is no method desconto, then I think you’ll solve it better.

A code possibly a little better:

public class Boleto {
    private Aluno aluno;
    private String referencia;
    private double valor;

    public Boleto(Aluno aluno, String referencia, double valor) {
        this.aluno = aluno;
        this.referencia = referencia;
        this.valor = valor * (aluno.ÉAprovado() ? 0.9 : 1;
    }
    public double getValor() { return valor; }
}

Obviously the method ÉAprovado() is part of the class Aluno, after all this is a student property and should be defined there. Boleto is only a consumer of student information. Each class has its own responsibility. It will have an algorithm looking through the student’s grades in the disciplines and will return a boolean indicated the student’s condition. The approval could even be defined by a policy class, but that is not necessary for this algorithm.