CODEWITHSUNDEEP
javaarraylistnestedbluej
Brian
Brian

Reputation: 119

IndexOutOfBoundsException when using nested lists

I'm building a basic battleship-style game in Java and am using nested lists to represent a game grid. However, I keep getting the IndexOutOfBoundsException when trying to put down a ship.

The game board has the constructor as follows

public Board(){
    theSea = new ArrayList<ArrayList<ShipInterface>>(10);
    for(int i = 0; i < theSea.size(); i++){
        theSea.set(i, new ArrayList<ShipInterface>(10));
    }
}

The method for placing the ship is as follows:

public void placeShip(ShipInterface ship, Position position, boolean isVertical) throws InvalidPositionException, ShipOverlapException{
    for(int i=0; i<ship.getSize(); i++){
        theSea.get((position.getX()-1) + i).set(position.getY()-1, ship);
    }
}

However, I get the error at the line theSea.get((position.getX()-1) + i).set(position.getY()-1, ship);

I'm a beginner so sorry if I'm missing some obvious bit of code!

Upvotes: 0

Views: 57

Answers (1)

James_D
James_D

Reputation: 209603

When you create a new list, it has size 0 (the value you pass to the ArrayList constructor is the initial capacity - the size is the number of elements it currently contains). So your Board() constructor doesn't add anything to theSea - the for loop is iterated zero times.

Consequently, theSea remains empty, and when you later call theSea.get(i) for any value of i, you get an ArrayIndexOutOfBoundsException.

So you probably intend to do

public Board(){
    theSea = new ArrayList<ArrayList<ShipInterface>>(10);
    for(int i = 0; i < 10; i++){
        theSea.add(new ArrayList<ShipInterface>(10));
    }
}

Note now that theSea contains 10 empty lists; i.e. theSea.get(i) will return a list of size 0 for 0 <= i < 10. Thus your placeShip method will work, but only as long as each list is populated with y ranging from 0 to 9, in order.

Upvotes: 5

Related Questions