Return random value from HashMap

Question

In the class Room I need to write a method to return a random exit from HashMap exits, or return null if there are no exits in that HashMap. I have tried using iterators and saving it the HashMap in a Set but nothing works.

public class Room 
{
private String description;
private HashMap<Direction, Room> exits;        // stores exits of this room.
public Set<Character> chars;  // stores the characters that are in this room.

/**
 * Create a room described "description". Initially, it has
 * no exits. "description" is something like "a kitchen" or
 * "an open court yard".
 * @param description The room's description.
 * Pre-condition: description is not null.
 */
public Room(String description) 
{
    assert description != null : "Room.Room has null description";
    this.description = description;
    exits = new HashMap<Direction, Room>();
    chars = new HashSet<Character>();
    sane();
}
/**
 * Define an exit from this room.
 * @param direction The direction of the exit.
 * @param neighbor  The room to which the exit leads.
 * Pre-condition: neither direction nor neighbor are null; 
 * there is no room in given direction yet.
 */
public void setExit(Direction direction, Room neighbor) 
{
    assert direction != null : "Room.setExit gets null direction";
    assert neighbor != null : "Room.setExit gets null neighbor";
    assert getExit(direction) == null : "Room.setExit set for direction that has neighbor";
    sane();
    exits.put(direction, neighbor);
    sane();
    assert getExit(direction) == neighbor : "Room.setExit has wrong neighbor";
}
 /**
 * Return the room that is reached if we go from this room in direction
 * "direction". If there is no room in that direction, return null.
 * @param direction The exit's direction.
 * @return The room in the given direction.
 * Pre-condition: direction is not null
 */
public Room getExit(Direction direction) 
{
    assert direction != null : "Room.getExit has null direction";
    sane();
    return exits.get(direction);
}

Direction:

public enum Direction
{
NORTH("north"), WEST("west"), SOUTH("south"), EAST("east");

private String name;

/**
 * Constructor with parameter.
 * Pre-condition: name is not null.
 */
private Direction(String name)
{
    assert name != null : "Direction.Direction has null name";
    this.name = name;
    assert toString().equals(name) : "Direction.Direction produces wrong toString";
}

/**
 * Return the direction name.
 */
public String toString()
{
    return name;
}
}

Any help will be appreciated

When using enum values as keys, you should use an [EnumMap](https://docs.oracle.com/javase/9/docs/api/java/util/EnumMap.html), not a HashMap. — VGR, Mar 22 '18 at 22:26

score 1 · Accepted Answer · answered Mar 22 '18 at 21:28

Try converting the map to a list something like this (inside Room class) :

public Direction getRandomExit(){
        List<Direction> directions = new ArrayList<Direction>(exits.keySet());
        if (directions.size()==0){
            return null;
        }
            Random rand = new Random();
            int randomIndex = rand.nextInt(directions.size());
            return directions.get(randomIndex);

    }

Return random value from HashMap

1 Answers1