How to set the key and value of an object creating an instance and put the values in the map?

Question

I only know how to hashmap in a way that is creating an instance in the put method to insert values.

Follow the way I do:

import java.util.Map;

public class Teste {

public static void main(String[] args){

//Exemplo com utilização de hashmap

    Map<Pessoa, Pessoa> example = new HashMap<Pessoa, Pessoa>();



    example.put(new Pessoa(12), new Pessoa("Aline"));
    example.put(new Pessoa(13), new Pessoa("Carla"));

    int key = 2;

    if(example.containsKey(key)){
        System.out.println("Valor é:" + key + " = " + example.get(key));

    }else{
        System.out.println("Não existe!");
    }
  }
}

But I couldn’t do it that way as you do it? example:

import java.util.Map;

public class Teste {

    public static void main(String[] args){



    //Exemplo com utilização de hashmap

        Map<Pessoa, Pessoa> example = new HashMap<Pessoa, Pessoa>();

        Pessoa pessoa;

        pessoa = new Pessoa();
        pessoa.setId(40);
        pessoa.setNome("Aline");

        example.put(pessoa.getId(), pessoa.getNome());

        int key = 2;

        if(example.containsKey(key)){
            System.out.println("Valor é:" + key + " = " + example.get(key));

        }else{
            System.out.println("Não existe!");
        }
    }




Class Pessoa:

package ibm;

public class Pessoa {
private Integer id;
private String nome;

Pessoa(Integer num){
 this.id    = num;
}

Pessoa(String nome){
    this.nome = nome;
}

public Integer getId() {
    return id;
}

public void setId(Integer id) {
    this.id = id;
}

public String getNome() {
    return nome;
}

public void setNome(String nome) {
    this.nome = nome;
}

}

Answer 1

The key and value types of your Map do not match what you are trying to insert into it.

Map is a type of collection that holds keys and values, with the goal of you locating a value through your key. In case you want the key to be an integer (id) and the value to be the name of the person (String). Then your Map should reflect this. In other words...

This line:

Map<Pessoa, Pessoa> example = new HashMap<Pessoa, Pessoa>();

should be exchanged for:

Map<Integer, String> example = new HashMap<Integer, String>();

or better still, by:

Map<Integer, String> example = new HashMap<>();

---

UPDATING: On second thought, maybe you want to do a little different and locate a Person through your id. In that case you should declare your Map like this:

Map<Integer, Pessoa> example = new HashMap<>();

and change your put() thus:

example.put(pessoa.getId(), pessoa);

Once done, you can see what the name of the person is like:

Pessoa pessoa = example.get(id);
System.out.println("Nome: " + pessoa.getNome());