toArray Dynamic behaviour

public class ToArrayTest {

public static void main(String[] args) {

ArrayList<String> arrayList = new ArrayList<String>();
arrayList.add("1");
arrayList.add("2");
arrayList.add("3");
arrayList.add("4");

//what happens here??, since I have allocated new String[0] for single element, will it return single element or all elements ??
String[] array = arrayList.toArray(new String[0]); 
System.out.println(array.length);

}
}

Output:  4

As per spec, it's going to create a new array, if it does not fit in.

Returns an array containing all of the elements in this list in proper sequence (from first to last element); the runtime type of the returned array is that of the specified array. If the list fits in the specified array, it is returned therein. Otherwise, a new array is allocated with the runtime type of the specified array and the size of this list. 

Collections emptyList()

Can you guess the output for the below program ?
import java.util.Collections;
import java.util.List;

public class CollectionsTest {

private List<String> pool = Collections.<String> emptyList();

public List<String> call1() {
pool.add("Hello");
return pool;
}

public static void main(String[] args) {
CollectionsTest collectionsTest = new CollectionsTest();
List<String> call1 = collectionsTest.call1();
System.out.println(call1);
call1.add("one more added..");
System.out.println(call1);
}
}

Output:

Exception in thread "main" java.lang.UnsupportedOperationException

at java.util.AbstractList.add(AbstractList.java:131)

at java.util.AbstractList.add(AbstractList.java:91)

at CollectionsTest.call1(CollectionsTest.java:9)

at CollectionsTest.main(CollectionsTest.java:15)

In short:

Collections.emptyList() returns an immutable list, i.e., a list to which you cannot add or remove elements.

Then, why should we use at all ? What is the purpose of this ?

look here@ http://gochev.blogspot.in/2010/07/using-of-collectionsemptylist-right-way.html

Best Regards,

Kondal Kolipaka