删除和替换ArrayList中的重复项

Question

How do I remove duplicate numbers on ArrayList and replace them with new ones?

I want to print the numbers without them duplicating.

This is my code:

import java.util.ArrayList;
import java.util.HashSet;
import java.util.Set;
import javax.swing.JOptionPane;

public class Test {
    public static void main(String[] args) {
        ArrayList<Integer> al = new ArrayList<Integer>();

        int opt = Integer.parseInt(JOptionPane.showInputDialog("How many numbers?");
        for (int i=0 ; i < opc ; i++) {
            al.add(Integer.parseInt(JOptionPane.showInputDialog("Which numbers?")));
        }

        Set<Integer> s = new HashSet<>();
        for (Integer d : al){
            if (s.add(d) == false)
                JOptionPane.showMessageDialog(null,"The number " + d + " was duplicated in position " + al.lastIndexOf(d));
                JOptionPane.showMessageDialog(null,"Replace new number"); //This is where I would like to replace the numbers if possible
            }
        JOptionPane.showMessageDialog("Your numbers without duplicates: "); //This is where it would print
        }
    }
}

Answer 1

Prevent from entering duplicate numbers when the user enters them, instead of checking and replacing them later.

Do it in this place:

for (int i=0 ; i < opc ; i++) {
    al.add(Integer.parseInt(JOptionPane.showInputDialog("Which numbers?")));
}

Chceck if a number already exists, if yes then ask for another not duplicated, if yes then add it and ask for next number :

for (int i=0 ; i < opc ; i++) {
    int myNumber = Integer.parseInt(JOptionPane.showInputDialog("Which numbers?"));
    while( true ){
        if( ! al.contains( myNumber ))
           al.add( myNumber );
           break;
        }
        myNumber = Integer.parseInt(JOptionPane.showInputDialog("This number is a duplicate, enter another number again"));
    }
}

======== EDIT ==================

I've corrected the example. There is missing { after if in the above (previous) one:

public class MmuClass {

    public static void main(String... wwwx) {
        List<Integer> lst = Arrays.asList(4, 2, 6, -6, 9);

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

        for (int i = 0; i < 5; i++) {
            int myNumber = Integer.parseInt(JOptionPane.showInputDialog("Which numbers?"));
            while (true) {
                if (!al.contains(myNumber)) {
                    al.add(myNumber);
                    break;
                }
                myNumber = Integer.parseInt(
                        JOptionPane.showInputDialog("This number is a duplicate, enter another number again"));
            }
            al.stream().forEach(System.out::println);
        }
    }
}