Question

This is a chunk of code I’m using for Google’s antai challenge whenever I run it it seems to go into some endless loop then I get the stack trace at the bottom. I’m burnt out looking at this code I can’t for the life of me figure this out.

public class Node 
{
    private final int xCoord, yCoord;
    private int F, G, H;
    private Tile location;
    Node previousNode;
    private Tile [] neighbors;

    /*  
    G 
    the exact cost to reach this node from the starting node.
    H 
    the estimated(heuristic) cost to reach the destination from here.
    F = G + H 
    As the algorithm runs the F value of a node tells us how expensive we think it will         be to reach our goal by way of that node.
    */

    public Node(Tile loc)
    {
        location = loc;
        xCoord = location.getCol();
        yCoord = location.getRow();
        F=G=H=0;
        setNeighbors();
    }

    private void setNeighbors()
    {
        if(neighbors == null)
        {
            neighbors = new Tile[4];
        }
        neighbors[0] = new Tile(xCoord+1,yCoord);
        neighbors[1] = new Tile(xCoord-1,yCoord);
        neighbors[2] = new Tile(xCoord,yCoord+1);
        neighbors[3] = new Tile(xCoord,yCoord-1);//error occurs here!!!!!!
    }
}

        /**
 * Represents a tile of the game map.
 */
public class Tile implements Comparable<Tile> {
    private final int row;

    private final int col;

    /**
     * Creates new {@link Tile} object.
     * 
     * @param row row index
     * @param col column index
     */
    public Tile(int row, int col) {
        this.row = row;
        this.col = col;
    }

    /**
     * Returns row index.
     * 
     * @return row index
     */
    public int getRow() {
        return row;
    }

    /**
     * Returns column index.
     * 
     * @return column index
     */
    public int getCol() {
        return col;
    }

    /** 
     * {@inheritDoc}
     */
    @Override
    public int compareTo(Tile o) {
        return hashCode() - o.hashCode();
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public int hashCode() {
        return row * Ants.MAX_MAP_SIZE + col;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public boolean equals(Object o) {
        boolean result = false;
        if (o instanceof Tile) {
            Tile tile = (Tile)o;
            result = row == tile.row && col == tile.col;
        }
        return result;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public String toString() {
        return row + " " + col;
    }
    }

the actual error I’m receiving is:

Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
    at Node.setNeighbors(Node.java:37)
    at Node.<init>(Node.java:25)
    at AstarSearch.assessRoute(AstarSearch.java:73)
    at MyBot.gatherFood(MyBot.java:153)
    at MyBot.doTurn(MyBot.java:124)
    at AbstractSystemInputParser.processLine(AbstractSystemInputParser.java:54)
    at AbstractSystemInputReader.readSystemInput(AbstractSystemInputReader.java:18)
    at MyBot.main(MyBot.java:25)

any help is appreciated

Answer 1

I don’t know what this Google challenge is, so this may not be of much use (ie I don’t know if you have access to the JVM), though it is a generic method to help diagnose this kind of problem.

I suggest turning on the JVM flag -XX:+HeapDumpOnOutOfMemoryError, and running your code again. An OutOfMemoryError will cause the heap to be dumped. You can then analyse this offline using something like Eclipse MAT.