How to iterate through ArrayList derived from object

Question

Newbie to Java and Android...

I am using a class to store a group of Google Map LatLng points to iterate through. Here is the class I am using to assign an Arraylist to an Object:

public class GeoPoints implements Iterable<String>, Iterator<String> {

private HashMap<String, Object> internalStorage = new HashMap<String, Object>();


private int count = 0;

public void add(String key, Object value) {
    internalStorage.put(key, value);
}

public Object get(String key) {
    return internalStorage.get(key);
}

@Override
public boolean hasNext() {
    if (count <  internalStorage.size()) {
        return true;
    }
    return false;
}

@Override
public String next() {
    if (count == internalStorage.size()) throw new IndexOutOfBoundsException();

    count++;

    return (String) internalStorage.keySet().toArray()[count - 1];
}

@Override
public void remove() {
    throw new UnsupportedOperationException();
}

@Override
public Iterator<String> iterator() {
    return this;
}

}

I am placing the points like this:

geoPoints = new GeoPoints();



    // Load GeoPoints ArrayList...
    List<LatLng> points = new ArrayList<LatLng>();

    points.add(new LatLng(45.778754, -124.811288));
    points.add(new LatLng(28.781740, -124.350814));
    points.add(new LatLng(48.712660, -60.982386));
    points.add(new LatLng(20.354554, -58.794457));


    geoPoints.add("US_MAP", points);

To access the object I am using a for loop as follows:

for (String key : geoPoints ) {

    Object obj = geoPoints.get(key);

}

At this point, I can debug and see that the Object obj contains the ArrayList I created with the four points above.

For the life of me I cannot figure out how to access these Arraylist values in order to Iterate or loop through the values.

I have tried assigning the obj to an arraylist iterator as such:

ArrayList<?> myTestItr = geoPoints.get(key);

Which does not work, I am sure for obvious reasons... :)

I am sure there is a simple answer to this (using a Iterator wildcard, etc) but I am coming up short.

Any and all help is greatly appreciated!

Thanks in advance!

Answer 1

Have you tried declaring your map as follows:

private HashMap<String, List<LatLng>> internalStorage = new HashMap<String, List<LatLng>>();

This would mean you can only add the type List<LatLng> but you can easily iterate over the entries.

You have to edit your two methods as well:

public void add(String key, List<LatLng>value) {
    internalStorage.put(key, value);
}

public List<LatLng>get(String key) {
    return internalStorage.get(key);
}

Answer 2

尝试以编程方式进行投射：

ArrayList<?> myTestItr = (ArrayList<?>) geoPoints.get(key);

Answer 3

You have to cast the Object class to ArrayList.

Casting is simply like, Converting the object to a supported Class Type.

If its not supported, it will throw a java.lang.ClassCastException

ArrayList<?> myTestItr = (ArrayList<?>) geoPoints.get(key);

This should solve your issue.

Answer 4

With thanks to all, here is the solution and implementation:

First the new class with List LatLng type:

public class GeoPoints implements Iterable<String>, Iterator<String> {


private HashMap<String, List<LatLng>> internalStorage = new HashMap<String, List<LatLng>>();


private int count = 0;

public void add(String key, List<LatLng>value) {
    internalStorage.put(key, value);
}

public List<LatLng> get(String key) {
    return internalStorage.get(key);
}

@Override
public boolean hasNext() {
    if (count <  internalStorage.size()) {
        return true;
    }
    return false;
}

@Override
public String next() {
    if (count == internalStorage.size()) throw new IndexOutOfBoundsException();

    count++;

    return (String) internalStorage.keySet().toArray()[count - 1];
}

@Override
public void remove() {
    throw new UnsupportedOperationException();
}

@Override
public Iterator<String> iterator() {
    return this;
}

}

Adding to the object:

geoPoints = new GeoPoints();

// Load GeoPoints ArrayList...
List<LatLng> points = new ArrayList<LatLng>();

points.add(new LatLng(45.778754, -124.811288));
points.add(new LatLng(28.781740, -124.350814));
points.add(new LatLng(48.712660, -60.982386));
points.add(new LatLng(20.354554, -58.794457));


geoPoints.add("US_MAP", points);

To iterate through the collection:

for (String key : geoPoints) {

        List<LatLng> geoPointsXY = geoPoints.get(key);

        Iterator geoPtsItr = geoPointsXY.iterator();


        while (geoPtsItr.hasNext()){

            LatLng oNxtLatLng = (LatLng) geoPtsItr.next();

            double yt = oNxtLatLng.latitude;
            double nt = oNxtLatLng.longitude;

            // Verify Coords here:...




        }

}