Class that implements Comparable must compare by a String field in lexicographic order

Question

How do I order a list of people by name? For understanding, follow the code:

public class Pessoa implements Comparable<Pessoa> {
    
    private String nome;
    private int idade;
    private String sexo;
    
    Pessoa(String nome, int idade, String sexo) {
        this.nome = nome;
        this.idade = idade;
        this.sexo = sexo;
    }   

    public String getNome() {
        return nome;
    }

    public void setNome(String nome) {
        this.nome = nome;
    }
    
    public int getIdade() {
        return idade;
    }

    public void setIdade(int idade) {
        this.idade = idade;
    }

    @Override
    public int compareTo(Pessoa outra) {
        if(this.nome.length() < outra.getNome().length())
            return -1;
        if(this.nome.length() > outra.getNome().length())
            return 1;
        
        return 0;
    }

}

In the test class I call the method sort(), however, is not coming out lexicographically, because it is names (strings) was what I expected.

I know the class String implementing Comparable and in this case I’m dealing with an object Pessoa, but if I tell the class to implement Comparable, shouldn’t I be ordered lexicographically? How would I look in these cases? Where am I going wrong? You would have to load only strings in the list and not the whole object?

Test class:

import java.util.Arrays;
import java.util.Collections;
import java.util.List;

public class TestaPessoa {
    
    public static void main(String[] args) {
        
        Pessoa p2 = new Pessoa("Joel", 34, "Masculino");
        Pessoa p6 = new Pessoa("Sebastião", 70, "Masculino");
        Pessoa p4 = new Pessoa("Ozeias", 41, "Masculino");
        Pessoa p5 = new Pessoa("Neuza", 59, "Feminino");
        Pessoa p1 = new Pessoa("Joabe", 33, "Masculino");
        Pessoa p3 = new Pessoa("Regiane", 37, "Feminino");
        
        
        List<Pessoa> pessoa = Arrays.asList(p2, p6, p4, p5, p1, p3);
        
        Collections.sort(pessoa);
        
        for(Pessoa p : pessoa) {
            System.out.println(p.getNome());
        }
        
    }
}

Exit:

Joel
Neuza
Joabe
Ozeias
Regiane
Sebastião

Answer 1

length() returns the size of the string, so you are sorting by the number of characters in the name.

If you want the lexicographical order, compare the strings themselves. In this case, strings already have the method compareTo implemented, so just use it:

public int compareTo(Pessoa outra) {
    return this.nome.compareTo(outra.nome);
}

---

If you want to ignore the difference between upper and lower case letters, you can use compareToIgnoreCase.

---

Remembering that, case the class Pessoa did not implement Comparable, would also be possible to sort by name, using a Comparator:

Collections.sort(pessoa, new Comparator<Pessoa>() {
    @Override
    public int compare(Pessoa p1, Pessoa p2) {
        return p1.getNome().compareTo(p2.getNome());
    }
});

Or, from Java 8, just use method References:

Collections.sort(pessoa, Comparator.comparing(Pessoa::getNome));