public abstract boolean remove (Object o)

Removes a single instance of the specified element from this collection, if it is present (optional operation). More formally, removes an element e such that (o==null ? e==null : o.equals(e)), if this collection contains one or more such elements. Returns true if this collection contained the specified element (or equivalently, if this collection changed as a result of the call).

o    element to be removed from this collection, if present

Returns:  true if an element was removed as a result of this call

ClassCastException    if the type of the specified element is incompatible with this collection (optional)
NullPointerException    if the specified element is null and this collection does not permit null elements (optional)
UnsupportedOperationException    if the remove operation is not supported by this collection