How to get non repeating random number pairs,elements can repeat

I'm currently programming a BattleShip game in Java, I randomly generate x, then y for the first cell of the ship,

public class Cell implements Comparable<Cell> {


    private final int x;
    private final int y;

    public int getX() {
        return x;
    }

    public int getY() {
        return y;
    }

    Cell(int xc, int yc) {
        x = xc;
        y = yc;
    }


    public Cell continueWithDirection(Direction d) {
        switch (d) {
            case ROW -> {
                return new Cell(x + 1, y);
            }

            case COLUMN -> {
                return new Cell(x, y + 1);
            }
        }
        ;

        return new Cell(x, y);
    }
}

//file 2

import java.util.Random;

public enum Direction {
    ROW,
    COLUMN;

  private static final Random randomizer=new Random();
  
    static Direction random(){
        boolean b = randomizer.nextBoolean();
        if (b) {
            return Direction.ROW;
        } else {
            return Direction.COLUMN;
        }
    }
}

Cell[] cells = new Cell[size];
cells[0] = new Cell(randomizer.nextInt(getAreaWidth() - size + 1), randomizer.nextInt(getAreaHeight() - size + 1));

for (int i = 1; i < cells.length; i++) {
    cells[i] = cells[i - 1].continueWithDirection(getDirection());
}

return cells;

and then choose a random direction (either up or right) for the other 2 cells of the ship the first cell is placed from 0 to bound-shipSize + 1 x and y bound, so I guarantee that all ships will be placed in the border area, but how do I implement random coordinate generation without repeating the same x and y together. I thought to randomly generate only the first ship, then just randomly go in some direction from the ship and put a new ship, but even so I have to store an array of all ships, and detect collisions. How can I better implement this algorithm