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user13558
Asked: 2020-12-01 03:32:23 +0800 CST 2020-12-01 03:32:23 +0800 CST

sort method to sort the ArrayList in Java

  • 772

I have declared an integer dynamic in Java, that is:

ArrayList<Integer> lista = new ArrayList<Integer>();

... I'm already adding numbers to this one.

lista.add(5); lista.add(7); lista.add(3);

What I want is to order that list, and make it look like this 3, 5, 7, and for that, I tried to use a method called sort, as follows.

lista.sort();

But he asks me for an argument that I don't know. I would like to order it from smallest to largest, although if I can sort it from largest to smallest, it doesn't matter, because then I can flip the list.

The error I have is:

The method sort(Comparator<? super Integer>) in the type ArrayList<Integer> is not applicable for the arguments ()

How do I go about applying that sort method to the list?

java

4 Answers

  1. Best Answer

    Before Java 8 you can call the .sort()like this:

    lista.sort(new Comparator<Integer>() {
    @Override
    public int compare(Integer o1, Integer o2) {
        return o1.compareTo(o2);
    }
});

    Demonstration .

    As of Java 8, you can simplify the call using a lambda expression:

    lista.sort((o1, o2) -> o1.compareTo(o2));

    Demonstration .

    Or you can also use the answer proposed by @Error404.

    • 17

  2. You can do it by importing the class Collections:

    import java.util.Collections;

    And using the method sortas follows:

    Collections.sort(lista);

    So your complete example would be:

    import java.util.ArrayList;
import java.util.Collections;

public class OrdenaNumeros
{
  public static void main(String[] args)
  {
    ArrayList<Integer> lista = new ArrayList<Integer>();
    lista.add(5); 
    lista.add(7); 
    lista.add(3);

    Collections.sort(lista);

    for (Integer numero: lista) {
        System.out.println(numero);
    }   

  }
}

    Which would give you the following output:

    3
5
7
    • 16 
  3. ArrayList<Integer> lista = new ArrayList<Integer>();
lista.add(5);
lista.add(7);
lista.add(3);

Collections.sort(lista, Integer::compareTo);
for (Integer in : lista) {
    System.out.println(in);
}
    • 2 
  4. import java.util.ArrayList;
import java.util.Collections;

public class OrdenaNumeros
{
  public static void main(String[] args)
  {
    ArrayList<String> lista = new ArrayList<String>();
    lista.add("RE00998"); 
    lista.add("RE00999"); 
    lista.add("REA1000");
    lista.add("REA1001");

    Collections.sort(lista);

    for (String datos: lista) {
        System.out.println(datos);
    }   

  }
}
    • 0