将数组列表中的单个值存储到数组中

Question

I want to get values from an arraylist so that I can graph them but I am having trouble getting them into an array. In this loop, I am looping over my sorted hashmap and attempting to store values in an array(doesn't work).

long v [] = null;

for(Map.Entry<String,NumberHolder> entry : entries)
{
       v = entry.getValue().singleValues;
}

This is my NumberHolder class

private static class NumberHolder
{
    public int occurrences = 0;
    public int sumtime_in_milliseconds = 0; 
    public ArrayList<Long> singleValues = new ArrayList<Long>();
}

I eventually want an array filled with single values so that I can graph it.

EDIT

This is what I have now, and Eclipse gives me this never ending error suggestions of converting my array to Object[] which gives me problems when using dataset.addSeries for my graph.

for(Map.Entry<String,NumberHolder> entry : entries)
{ 
   graphMaker(entry.getValue().occurrences,entry.getValue().singleValues.toArray());
}                                        


public static void graphMaker(int totalValues, Object[] objects)
{

    int bin = 1000;
    HistogramDataset dataset = new HistogramDataset();
    dataset.setType(HistogramType.RELATIVE_FREQUENCY);
    dataset.addSeries("Histogram",objects,bin, 0, 120000);

Answer 1

You can't assign an ArrayList to an Array like that. Maybe you could use the toArray method:

long v [] = null;

for(Map.Entry<String,NumberHolder> entry : entries)
{
   v = entry.getValue().singleValues.toArray(new long[0]);
}

Answer 2

Pretty straightforward:

final ArrayList<Long> t = entry.getValue().singleValues;
v = new long[t.size()];
for (int i = 0; i < v.length; ++i) v[i] = t.get[i];

Edit: fixed handling of primitive type

Answer 3

v = entry.getValue().singleValues.toArray(new long[0]);

Answer 4

You can't do it directly because long is not equal to Long .

You can use the Apache Commons Lang Library . There is a class called ArrayUtils that have a function called toPrimitive .

If you use that function you can do:

for(Map.Entry<String,NumberHolder> entry : entries)
{
   v = ArrayUtils.toPrimitive(entry.getValue().singleValues.toArray(new Long[0]));
}

Or, if you don't want to use the library, you can do the following:

for(Map.Entry<String,NumberHolder> entry : entries)
{
   v = new long[entry.getValue().singleValues.size()];
   for (int i=0; i<v.length; i++) {
       v[i]=entry.getValue().singleValues.get(i);
   }
}

Answer 5

Try the following:

Set<Long> values = new HashSet<Long>();
Iterator<NumberHolder> it = entries.keySet().iterator();
while(it.hasNext()) {
    NumberHolder numberHolder = it.next();
    values.addAll(numberHolder.singleValues;
}
Long[] v1 = values.toArray();
// transform to primitive long array
long[] v = new long[v1.size()];
for(int i = 0; i < v1.size(); i++) {
    v[i] = v1[i];
}