Java Utililty Methods Collection to Array

List of utility methods to do Collection to Array

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Description

The list of methods to do Collection to Array are organized into topic(s).

Method

ObjectconvertToArray(Collection collection)
convert To Array 
Iterator iter = collection.iterator();
if (!iter.hasNext())
    return null;
Class objCls = iter.next().getClass();
if (objCls == Integer.class) {
    return convertToIntArray(collection);
} else if (objCls == Long.class) {
    return convertToLongArray(collection);
...
double[]convertToArray(Collection input)
convert To Array 
double[] result = new double[input.size()];
int count = 0;
for (double d : input) {
    result[count++] = d;
return result;
T[]convertToArray(Collection items)
convert To Array 
return (T[]) items.toArray();
String[]toArray(Collection c)
Returns a string array contains all the String object in the Collection c. 
if (c == null || c.size() == 0) {
    return EMPTY_STRING_ARRAY;
String[] result = new String[c.size()];
int i = 0;
for (Iterator iter = c.iterator(); iter.hasNext();) {
    result[i++] = (String) iter.next();
return result;
int[]toArray(Collection coll)
to Array 
int[] target = new int[coll.size()];
int pos = 0;
for (int i : coll)
    target[pos++] = i;
return target;
byte[]toArray(Collection bytes)
Converts a Collection of Number to a byte array. 
byte[] array = new byte[bytes.size()];
Iterator<? extends Number> iter = bytes.iterator();
for (int i = 0; i < bytes.size(); i++) {
    array[i] = iter.next().byteValue();
return array;
T[]toArray(Collection c, T[] arr)
Copies all elements from collection to array and asserts that array is big enough to hold the collection. 
T[] a = c.toArray(arr);
assert a == arr;
return arr;
Object[]toArray(Collection collection)
to Array 
return collection.toArray(new Object[collection.size()]);
Object[][]toArray(Collection tests)
to Array 
Object[][] result = new Object[tests.size()][];
int i = 0;
for (Object testCase : tests) {
    result[i++] = new Object[] { testCase };
return result;
boolean[]toArray(Collection list)
Converts a collection ( List , Set ...) of Boolean objects to a boolean[] . 
return asPrimitiveArray(list.toArray(new Boolean[list.size()]));