Inheritance, polymorphism and access to methods

Question

I have 3 classes and 1 enum:

public class Pessoa {
        private TipoPessoa tipo;
        public TipoPessoa getTipo() {
            return tipo;
        }
        public void setTipo(TipoPessoa tipo) {
            this.tipo = tipo;
        }
      }



public class PessoaF  extends Pessoa{
                private String cpf;
                public String getCpf() {
                    return cpf;
                }
            public void setCpf(String cpf) {
                this.cpf = cpf;
            }
         }



public class PessoaJ extends Pessoa{
            private String cnpj;
            public String getCnpj() {
                return cnpj;
            }
            public void setCnpj(String cnpj) {
                this.cnpj = cnpj;
            }
        }



public enum TipoPessoa {
            PESSOAFISICA, PESSOAJURIDICA;
        }

I want you to be able to create an instance equivalent to the enumerator applied to the type:

For example, if I was able to access the members (attributes, fields and methods) of the Personal class, I could access it, because it would call the correct constructor:

Pessoa p1 = new PessoaF();
p1.setCpf = 32443265332;

But with inheritance I cannot access the members of a daughter class through an instance created from a parent class. So how to proceed?

I modified Enum, implementing an abstract method that returns me the constructor I want to use according to the type of person set:

public enum TipoPessoa {
    PESSOAFISICA (0, "Pessoa Fisica") {
        @Override
        public Pessoa obterPessoa() {
            return new PessoaF();
        }
    },
    PESSOAJURIDICA (1, "Pessoa Juridica") {
        @Override
        public Pessoa obterPessoa() {
            return new PessoaJ();
        }
    };



    public abstract Pessoa obterPessoa();


    private TipoPessoa(){}
    private TipoPessoa(Integer cod, String desc) {
        this.cod = cod;
        this.desc = desc;
    }

    private Integer cod;
    private String desc;
    public Integer getCod() {
        return cod;
    }
    public void setCod(Integer cod) {
        this.cod = cod;
    }
    public String getDesc() {
        return desc;
    }
    public void setDesc(String desc) {
        this.desc = desc;
    }
 }

with this modification I am creating the object as follows:

Pessoa p1 = TipoPessoa.PESSOAFISICA.obterPessoa();

When I ask him to print the type of the created object he tells me he created it correctly:

 System.out.println(p1.getClass());
 Retorno : class Pessoas.PessoaF

But I still can’t access the method setCpf() that is within the class PessoaF.

I want to create a person and according to the value set in the type attribute. And that this created object can access members according to the selected enumerator option. How to proceed?

Answer 1

I think you want to create a instance and not a resort.

I don’t like the term attribute, I prefer field.

You can access all public members of the object type at that time. You cannot access members of a type that is part of that object, but is not the type being used at that time. If the type is the father, can only access its members, can not access the members of the child type.

If you can guarantee that the object is of the child type can make a cast, which is a type conversion (it doesn’t necessarily change something in the data, it just tells the compiler that it wants to use a more specialized type. There it is allowed to access the members of the type son, and of the father also because the son always has everything the father has.

In general if the cast failed will generate an error or the result will be null. There are cases where the compiler can identify that it is not possible to compile or let compile.

In this example it doesn’t make much sense to declare p1 as Pessoa if you know you need it like PessoaFisica, but it is possible, then you can write:

((PessoaFisica)p1).cpf

I put in the Github for future reference.

Performance will be worse if there is no optimization the compiler is prepared to perform.

It can also be done with reflection, but it is absurdly worse and unreasonable.

Just because a tool solves what you wanted doesn’t mean it’s right to use it.