How to make the random placing of ships not overlap any ships when placing in battleships

Im making the game battleships on the computer and wonder how i can make the ships not overlap each other when randomly placing them. My code right now looks like this:

public class BattleshipSetup {

    public static class Boat {
        int size;
    }
    public static class AircraftCarrier extends Boat {
        public AircraftCarrier() {
            size = 5;
        }
    }
    public static class Battleship extends Boat {
        public Battleship() {
            size = 4;
        }
    }
    public static class Destroyer extends Boat {
        public Destroyer() {
            size = 3;
        }
    }
    public static class Submarine extends Boat {
        public Submarine() {
            size = 3;
        }
    }
    public static class PatrolShip extends Boat {
        public PatrolShip() {
            size = 2;
        }
    }
    public static class GridSetup {
        int[][] grid = {{0, 0, 0, 0, 0, 0, 0}, {0, 0, 0, 0, 0, 0, 0},
                {0, 0, 0, 0, 0, 0, 0}, {0, 0, 0, 0, 0, 0, 0}, {0, 0, 0, 0, 0, 0, 0},
                {0, 0, 0, 0, 0, 0, 0}, {0, 0, 0, 0, 0, 0, 0}};
        public void setGrid() {
            Boat[] ship;
            ship = new Boat[5];
            ship[0] = new AircraftCarrier();
            ship[1] = new Battleship();
            ship[2] = new Destroyer();
            ship[3] = new Submarine();
            ship[4] = new PatrolShip();
            for (int i = 0; i < 5; i++) {
                int way = (int) (Math.random() * 2);
                if (way == 0) {
                    int x = (int) (Math.random() * 7);
                    int y = (int) (Math.random() * (7 - ship[i].size));
                    for (int j = 0; j < ship[i].size; j++) {
                        grid[x][y + j] = i + 1;
                    }
                }
                if (way == 1) {
                    int x = (int) (Math.random() * (7 - ship[i].size));
                    int y = (int) (Math.random() * 7);
                    for (int j = 0; j < ship[i].size; j++) {
                        grid[x + j][y] = i + 1;
                    }
                }
            }
        }
        public int[][] getGrid() {
            return grid;
        }
    }
}`

The thing now is that sometimes when it places ships it puts one ship partially over another one and that is not supossed to be possible.