Is it possible to instantiate ArrayList dynamically in java?

Question

Is it possible to instantiate ArrayList dynamically in java?

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#1 by (1 votes)

1

For example, if I need to create arraylists for each person who registers on my system:

ArrayList pessoa1 ArrayList();
ArrayList pessoa2 ArrayList();
ArrayList pessoa3 ArrayList();

The problem is that I do not know how many people are going to register so it would have to be created dynamically, type:

for(int i = 0; i < numeroPessoasCadastradas; i++){
    pessoa[i] = new ArrayList();
}

Is it possible to do something like this?

java

asked by anonymous 27.03.2017 / 01:53

1 answer

why does the loop while True access the if and the else in sequence to each complete loop in that code? PSD in 1920px getting huge in 1366px resolution

score 1 · Accepted Answer

It is possible, but in the way you wrote, pessoa[] is only a Array , and Arrays do not grow dynamically as you would like:

import java.util.ArrayList;

public class MeuPequenoArray {

    public static void main(String[] args) {

        int numeroPessoasCadastradas = 12345; // tamanho fixo
        ArrayList[] pessoa = new ArrayList[numeroPessoasCadastradas];

        for (int i = 0; i < numeroPessoasCadastradas; i++) {
            pessoa[i] = new ArrayList();
        }
    }
}

A possible solution is to create a List of ArrayLists - or a ArrayList of ArrayLists :

import java.util.ArrayList;

public class MeuEnormeArrayList {

    public static void main(String[] args) {

        int numeroPessoasCadastradas = 12; // esse número não importa mais
        ArrayList<ArrayList> pessoa = new ArrayList<ArrayList>();

        for(int i = 0; i < numeroPessoasCadastradas; i++){
            pessoa.add(new ArrayList<>());
        }
    }   
}