Framework. With the advent of collections, Vector was reengineered to extend AbstractList and
to implement the List interface. With the release of JDK 5, it was retrofitted for generics and
reengineered to implement Iterable. This means that Vector is fully compatible with collections,
and a Vector can have its contents iterated by the enhanced for loop.
Vector is declared like this:
class Vector<E>
Here, E specifies the type of element that will be stored.
Here are the Vector constructors:
Vector( )
Vector(int size)
Vector(int size, int incr)
Vector(Collection<? extends E> c)
The first form creates a default vector, which has an initial size of 10. The second form creates
a vector whose initial capacity is specified by size. The third form creates a vector whose
initial capacity is specified by size and whose increment is specified by incr. The increment
specifies the number of elements to allocate each time that a vector is resized upward. The
fourth form creates a vector that contains the elements of collection c.
All vectors start with an initial capacity. After this initial capacity is reached, the next
time that you attempt to store an object in the vector, the vector automatically allocates
space for that object plus extra room for additional objects. By allocating more than just the
required memory, the vector reduces the number of allocations that must take place. This
reduction is important, because allocations are costly in terms of time. The amount of extra
space allocated during each reallocation is determined by the increment that you specify
when you create the vector. If you don't specify an increment, the vector 's size is doubled
by each allocation cycle.
Vector defines these protected data members:
int capacityIncrement;
int elementCount;
Object[ ] elementData;
The increment value is stored in capacityIncrement. The number of elements currently in the
vector is stored in elementCount. The array that holds the vector is stored in elementData.
In addition to the collections methods defined by List, Vector defines several legacy
methods, which are summarized in Table 17-15.
Because Vector implements List, you can use a vector just like you use an ArrayList
instance. You can also manipulate one using its legacy methods. For example, after you
instantiate a Vector, you can add an element to it by calling addElement( ). To obtain the
element at a specific location, call elementAt( ). To obtain the first element in the vector, call
firstElement( ). To retrieve the last element, call lastElement( ). You can obtain the index of an
element by using indexOf( ) and lastIndexOf( ). To remove an element, call removeElement( )
or removeElementAt( ).
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