Java problem iterating through a treemap collection of classes

Question

Im trying to iterate through a Treemap of the class Tile() using:

Map map = new TreeMap();

Iterator itr = world.map.values().iterator();

while(itr.hasNext()){
     Tile t = ???;
     System.out.print(t.xCord+","+t.yCord+","+t.zCord);
}

How do I get the instance of the object Tile within the iterator? Or if theres some better way of doing this, plz let me know.

I've tried googling this, but I always end up looking at ways to iterate through pure data, like strings etc, and not Instanciations of class'...

Answer 1

Strings aren't pure data in Java, they are objects, so is the same:

Map map = new TreeMap();

Iterator itr = world.map.values().iterator();

while(itr.hasNext()){
    Tile t = (Tile)itr.next();
    System.out.print(t.xCord+","+t.yCord+","+t.zCord);
}

Or better:

Map<Key, Tile> map = new TreeMap<Key, Tile>();

Iterator<Tile> itr = world.map.values().iterator();

while(itr.hasNext()){
    Tile t = itr.next();
    System.out.print(t.xCord+","+t.yCord+","+t.zCord);
}

or even better:

Map<Key, Tile> map = new TreeMap<Key, Tile>();

for(Tile t : map.values){
    System.out.print(t.xCord+","+t.yCord+","+t.zCord);
}

p.s Key is the class of the key objects you're using

Answer 2

Tile t = (Tile) itr.next();

But note that using Iterators and especially raw collections is a very outdated way of writing Java. Much better would be using typed collections and the enhanced for loop:

Map<String, Tile> map = new TreeMap<String, Tile>();

for(Tile t : map.values()){
     System.out.print(t.xCord+","+t.yCord+","+t.zCord);
}

Answer 3

itr.next() gives the instance of the next element, as specified in the javadocs. Note that since your Map is of raw type, you will need a cast: Tile t = (Tile)itr.next(); but it is NOT type safe.

Even better solution is using generics as @Simone suggested

Answer 4

In an iterator you use

while(itr.hasNext()){
     Tile t = itr.next(); ...

However, you'd also have to cast the tile unless you gave the type with generics:

Map<Whatever,Tile> map = new TreeMap<Whatever,Tile>();
Iterator<Tile> itr = world.map.values().iterator();

Otherwise the iterator values will have to be cast - i.e. you'd have to correct your example (and the lines above) to

while(itr.hasNext()){
         Tile t = (Tile)itr.next(); ...

Answer 5

Within the loop, use itr.next() to retrieve the next Tile object from the Iterator. Currently this will return an Object, since you are using a raw-typed TreeMap. Instead use TreeMap<Key, Tile>, so that the values iterator will be an Iterator<Tile>.

Answer 6

Tile t = (Tile) itr.next()

This will give you the next instance of the class as well as move the iterator to the next instance.