java.util
class Vector

java.lang.Object java.util.AbstractCollection java.util.AbstractList java.util.Vector

All Implemented Interfaces:

Serializable, Cloneable, Collection, List, RandomAccess

Direct Known Subclasses:

Stack

Most common way to construct:

Vector v = new Vector();

Based on 132 examples

public class Vector
extends AbstractList
implements List, RandomAccess, Cloneable, Serializable

The {@code Vector} class implements a growable array of objects. Like an array, it contains components that can be accessed using an integer index. However, the size of a {@code Vector} can grow or shrink as needed to accommodate adding and removing items after the {@code Vector} has been created.

Each vector tries to optimize storage management by maintaining a {@code capacity} and a {@code capacityIncrement}. The {@code capacity} is always at least as large as the vector size; it is usually larger because as components are added to the vector, the vector's storage increases in chunks the size of {@code capacityIncrement}. An application can increase the capacity of a vector before inserting a large number of components; this reduces the amount of incremental reallocation.

The Iterators returned by Vector's iterator and listIterator methods are fail-fast: if the Vector is structurally modified at any time after the Iterator is created, in any way except through the Iterator's own remove or add methods, the Iterator will throw a ConcurrentModificationException. Thus, in the face of concurrent modification, the Iterator fails quickly and cleanly, rather than risking arbitrary, non-deterministic behavior at an undetermined time in the future. The Enumerations returned by Vector's elements method are not fail-fast.

Note that the fail-fast behavior of an iterator cannot be guaranteed as it is, generally speaking, impossible to make any hard guarantees in the presence of unsynchronized concurrent modification. Fail-fast iterators throw {@code ConcurrentModificationException} on a best-effort basis. Therefore, it would be wrong to write a program that depended on this exception for its correctness: the fail-fast behavior of iterators should be used only to detect bugs.

As of the Java 2 platform v1.2, this class was retrofitted to implement the {@link List} interface, making it a member of the Java Collections Framework. Unlike the new collection implementations, {@code Vector} is synchronized.

capacityIncrement

protected int capacityIncrement

The amount by which the capacity of the vector is automatically incremented when its size becomes greater than its capacity. If the capacity increment is less than or equal to zero, the capacity of the vector is doubled each time it needs to grow.

elementCount

protected int elementCount

The number of valid components in this {@code Vector} object. Components {@code elementData[0]} through {@code elementData[elementCount-1]} are the actual items.

elementData

protected Object[] elementData

The array buffer into which the components of the vector are stored. The capacity of the vector is the length of this array buffer, and is at least large enough to contain all the vector's elements.

Any array elements following the last element in the Vector are null.

Vector

public Vector()

Constructs an empty vector so that its internal data array has size {@code 10} and its standard capacity increment is zero.

Vector

public Vector(Collection c)

Constructs a vector containing the elements of the specified collection, in the order they are returned by the collection's iterator.

Parameters:

c - the collection whose elements are to be placed into this vector

Vector

public Vector(int initialCapacity)

Constructs an empty vector with the specified initial capacity and with its capacity increment equal to zero.

Parameters:

initialCapacity - the initial capacity of the vector

Vector

public Vector(int initialCapacity,
              int capacityIncrement)

Constructs an empty vector with the specified initial capacity and capacity increment.

Parameters:

initialCapacity - the initial capacity of the vector

capacityIncrement - the amount by which the capacity is increased when the vector overflows

add

public synchronized boolean add(Object e)

Appends the specified element to the end of this Vector.

Overrides:

add in class AbstractList

Parameters:

e - element to be appended to this Vector

Returns:

{@code true} (as specified by {@link Collection#add})

add

public void add(int index,
                Object element)

Inserts the specified element at the specified position in this Vector. Shifts the element currently at that position (if any) and any subsequent elements to the right (adds one to their indices).

Overrides:

add in class AbstractList

Parameters:

index - index at which the specified element is to be inserted

element - element to be inserted

addAll

public synchronized boolean addAll(Collection c)

Appends all of the elements in the specified Collection to the end of this Vector, in the order that they are returned by the specified Collection's Iterator. The behavior of this operation is undefined if the specified Collection is modified while the operation is in progress. (This implies that the behavior of this call is undefined if the specified Collection is this Vector, and this Vector is nonempty.)

Overrides:

addAll in class AbstractCollection

Parameters:

c - elements to be inserted into this Vector

Returns:

{@code true} if this Vector changed as a result of the call

addAll

public synchronized boolean addAll(int index,
                                   Collection c)

Inserts all of the elements in the specified Collection into this Vector at the specified position. Shifts the element currently at that position (if any) and any subsequent elements to the right (increases their indices). The new elements will appear in the Vector in the order that they are returned by the specified Collection's iterator.

Overrides:

addAll in class AbstractList

Parameters:

index - index at which to insert the first element from the specified collection

c - elements to be inserted into this Vector

Returns:

{@code true} if this Vector changed as a result of the call

addElement

public synchronized void addElement(Object obj)

Adds the specified component to the end of this vector, increasing its size by one. The capacity of this vector is increased if its size becomes greater than its capacity.

This method is identical in functionality to the {@link #add(Object) add(E)} method (which is part of the {@link List} interface).

Parameters:

obj - the component to be added

capacity

public synchronized int capacity()

Returns the current capacity of this vector.

Returns:

the current capacity (the length of its internal data array, kept in the field {@code elementData} of this vector)

clear

public void clear()

Removes all of the elements from this Vector. The Vector will be empty after this call returns (unless it throws an exception).

Overrides:

clear in class AbstractList

clone

public synchronized Object clone()

Returns a clone of this vector. The copy will contain a reference to a clone of the internal data array, not a reference to the original internal data array of this {@code Vector} object.

Overrides:

clone in class Object

Returns:

a clone of this vector

contains

public boolean contains(Object o)

Returns {@code true} if this vector contains the specified element. More formally, returns {@code true} if and only if this vector contains at least one element {@code e} such that (o==null ? e==null : o.equals(e)).

Overrides:

contains in class AbstractCollection

Parameters:

o - element whose presence in this vector is to be tested

Returns:

{@code true} if this vector contains the specified element

containsAll

public synchronized boolean containsAll(Collection c)

Returns true if this Vector contains all of the elements in the specified Collection.

Overrides:

containsAll in class AbstractCollection

Parameters:

c - a collection whose elements will be tested for containment in this Vector

Returns:

true if this Vector contains all of the elements in the specified collection

copyInto

public synchronized void copyInto(Object[] anArray)

Copies the components of this vector into the specified array. The item at index {@code k} in this vector is copied into component {@code k} of {@code anArray}.

Parameters:

anArray - the array into which the components get copied

elementAt

public synchronized Object elementAt(int index)

Returns the component at the specified index.

This method is identical in functionality to the {@link #get(int)} method (which is part of the {@link List} interface).

Parameters:

index - an index into this vector

Returns:

the component at the specified index

elements

public Enumeration elements()

Returns an enumeration of the components of this vector. The returned {@code Enumeration} object will generate all items in this vector. The first item generated is the item at index {@code 0}, then the item at index {@code 1}, and so on.

Returns:

an enumeration of the components of this vector

ensureCapacity

public synchronized void ensureCapacity(int minCapacity)

Increases the capacity of this vector, if necessary, to ensure that it can hold at least the number of components specified by the minimum capacity argument.

If the current capacity of this vector is less than {@code minCapacity}, then its capacity is increased by replacing its internal data array, kept in the field {@code elementData}, with a larger one. The size of the new data array will be the old size plus {@code capacityIncrement}, unless the value of {@code capacityIncrement} is less than or equal to zero, in which case the new capacity will be twice the old capacity; but if this new size is still smaller than {@code minCapacity}, then the new capacity will be {@code minCapacity}.

Parameters:

minCapacity - the desired minimum capacity

equals

public synchronized boolean equals(Object o)

Compares the specified Object with this Vector for equality. Returns true if and only if the specified Object is also a List, both Lists have the same size, and all corresponding pairs of elements in the two Lists are equal. (Two elements {@code e1} and {@code e2} are equal if {@code (e1==null ? e2==null : e1.equals(e2))}.) In other words, two Lists are defined to be equal if they contain the same elements in the same order.

Overrides:

equals in class AbstractList

Parameters:

o - the Object to be compared for equality with this Vector

Returns:

true if the specified Object is equal to this Vector

firstElement

public synchronized Object firstElement()

Returns the first component (the item at index {@code 0}) of this vector.

Returns:

the first component of this vector

get

public synchronized Object get(int index)

Returns the element at the specified position in this Vector.

Overrides:

get in class AbstractList

Parameters:

index - index of the element to return

Returns:

object at the specified index

hashCode

public synchronized int hashCode()

Returns the hash code value for this Vector.

Overrides:

hashCode in class AbstractList

indexOf

public int indexOf(Object o)

Returns the index of the first occurrence of the specified element in this vector, or -1 if this vector does not contain the element. More formally, returns the lowest index {@code i} such that (o==null ? get(i)==null : o.equals(get(i))), or -1 if there is no such index.

Overrides:

indexOf in class AbstractList

Parameters:

o - element to search for

Returns:

the index of the first occurrence of the specified element in this vector, or -1 if this vector does not contain the element

indexOf

public synchronized int indexOf(Object o,
                                int index)

Returns the index of the first occurrence of the specified element in this vector, searching forwards from {@code index}, or returns -1 if the element is not found. More formally, returns the lowest index {@code i} such that (i >= index && (o==null ? get(i)==null : o.equals(get(i)))), or -1 if there is no such index.

Parameters:

o - element to search for

index - index to start searching from

Returns:

the index of the first occurrence of the element in this vector at position {@code index} or later in the vector; {@code -1} if the element is not found.

insertElementAt

public synchronized void insertElementAt(Object obj,
                                         int index)

Inserts the specified object as a component in this vector at the specified {@code index}. Each component in this vector with an index greater or equal to the specified {@code index} is shifted upward to have an index one greater than the value it had previously.

The index must be a value greater than or equal to {@code 0} and less than or equal to the current size of the vector. (If the index is equal to the current size of the vector, the new element is appended to the Vector.)

This method is identical in functionality to the {@link #add(int, Object) add(int, E)} method (which is part of the {@link List} interface). Note that the {@code add} method reverses the order of the parameters, to more closely match array usage.

Parameters:

obj - the component to insert

index - where to insert the new component

isEmpty

public synchronized boolean isEmpty()

Tests if this vector has no components.

Overrides:

isEmpty in class AbstractCollection

Returns:

{@code true} if and only if this vector has no components, that is, its size is zero; {@code false} otherwise.

lastElement

public synchronized Object lastElement()

Returns the last component of the vector.

Returns:

the last component of the vector, i.e., the component at index size() - 1.

lastIndexOf

public synchronized int lastIndexOf(Object o)

Returns the index of the last occurrence of the specified element in this vector, or -1 if this vector does not contain the element. More formally, returns the highest index {@code i} such that (o==null ? get(i)==null : o.equals(get(i))), or -1 if there is no such index.

Overrides:

lastIndexOf in class AbstractList

Parameters:

o - element to search for

Returns:

the index of the last occurrence of the specified element in this vector, or -1 if this vector does not contain the element

lastIndexOf

public synchronized int lastIndexOf(Object o,
                                    int index)

Returns the index of the last occurrence of the specified element in this vector, searching backwards from {@code index}, or returns -1 if the element is not found. More formally, returns the highest index {@code i} such that (i <= index && (o==null ? get(i)==null : o.equals(get(i)))), or -1 if there is no such index.

Parameters:

o - element to search for

index - index to start searching backwards from

Returns:

the index of the last occurrence of the element at position less than or equal to {@code index} in this vector; -1 if the element is not found.

remove

public synchronized Object remove(int index)

Removes the element at the specified position in this Vector. Shifts any subsequent elements to the left (subtracts one from their indices). Returns the element that was removed from the Vector.

Overrides:

remove in class AbstractList

Parameters:

index - the index of the element to be removed

Returns:

element that was removed

remove

public boolean remove(Object o)

Removes the first occurrence of the specified element in this Vector If the Vector does not contain the element, it is unchanged. More formally, removes the element with the lowest index i such that {@code (o==null ? get(i)==null : o.equals(get(i)))} (if such an element exists).

Overrides:

remove in class AbstractCollection

Parameters:

o - element to be removed from this Vector, if present

Returns:

true if the Vector contained the specified element

removeAll

public synchronized boolean removeAll(Collection c)

Removes from this Vector all of its elements that are contained in the specified Collection.

Overrides:

removeAll in class AbstractCollection

Parameters:

c - a collection of elements to be removed from the Vector

Returns:

true if this Vector changed as a result of the call

removeAllElements

public synchronized void removeAllElements()

Removes all components from this vector and sets its size to zero.

This method is identical in functionality to the {@link #clear} method (which is part of the {@link List} interface).

removeElement

public synchronized boolean removeElement(Object obj)

Removes the first (lowest-indexed) occurrence of the argument from this vector. If the object is found in this vector, each component in the vector with an index greater or equal to the object's index is shifted downward to have an index one smaller than the value it had previously.

This method is identical in functionality to the {@link #remove(Object)} method (which is part of the {@link List} interface).

Parameters:

obj - the component to be removed

Returns:

{@code true} if the argument was a component of this vector; {@code false} otherwise.

removeElementAt

public synchronized void removeElementAt(int index)

Deletes the component at the specified index. Each component in this vector with an index greater or equal to the specified {@code index} is shifted downward to have an index one smaller than the value it had previously. The size of this vector is decreased by {@code 1}.

The index must be a value greater than or equal to {@code 0} and less than the current size of the vector.

This method is identical in functionality to the {@link #remove(int)} method (which is part of the {@link List} interface). Note that the {@code remove} method returns the old value that was stored at the specified position.

Parameters:

index - the index of the object to remove

removeRange

protected synchronized void removeRange(int fromIndex,
                                        int toIndex)

Removes from this List all of the elements whose index is between fromIndex, inclusive and toIndex, exclusive. Shifts any succeeding elements to the left (reduces their index). This call shortens the ArrayList by (toIndex - fromIndex) elements. (If toIndex==fromIndex, this operation has no effect.)

Overrides:

removeRange in class AbstractList

Parameters:

fromIndex - index of first element to be removed

toIndex - index after last element to be removed

retainAll

public synchronized boolean retainAll(Collection c)

Retains only the elements in this Vector that are contained in the specified Collection. In other words, removes from this Vector all of its elements that are not contained in the specified Collection.

Overrides:

retainAll in class AbstractCollection

Parameters:

c - a collection of elements to be retained in this Vector (all other elements are removed)

Returns:

true if this Vector changed as a result of the call

set

public synchronized Object set(int index,
                               Object element)

Replaces the element at the specified position in this Vector with the specified element.

Overrides:

set in class AbstractList

Parameters:

index - index of the element to replace

element - element to be stored at the specified position

Returns:

the element previously at the specified position

setElementAt

public synchronized void setElementAt(Object obj,
                                      int index)

Sets the component at the specified {@code index} of this vector to be the specified object. The previous component at that position is discarded.

The index must be a value greater than or equal to {@code 0} and less than the current size of the vector.

This method is identical in functionality to the {@link #set(int, Object) set(int, E)} method (which is part of the {@link List} interface). Note that the {@code set} method reverses the order of the parameters, to more closely match array usage. Note also that the {@code set} method returns the old value that was stored at the specified position.

Parameters:

obj - what the component is to be set to

index - the specified index

setSize

public synchronized void setSize(int newSize)

Sets the size of this vector. If the new size is greater than the current size, new {@code null} items are added to the end of the vector. If the new size is less than the current size, all components at index {@code newSize} and greater are discarded.

Parameters:

newSize - the new size of this vector

size

public synchronized int size()

Returns the number of components in this vector.

Overrides:

size in class AbstractCollection

Returns:

the number of components in this vector

subList

public synchronized List subList(int fromIndex,
                                 int toIndex)

Returns a view of the portion of this List between fromIndex, inclusive, and toIndex, exclusive. (If fromIndex and toIndex are equal, the returned List is empty.) The returned List is backed by this List, so changes in the returned List are reflected in this List, and vice-versa. The returned List supports all of the optional List operations supported by this List.

This method eliminates the need for explicit range operations (of the sort that commonly exist for arrays). Any operation that expects a List can be used as a range operation by operating on a subList view instead of a whole List. For example, the following idiom removes a range of elements from a List:

	    list.subList(from, to).clear();
 

Similar idioms may be constructed for indexOf and lastIndexOf, and all of the algorithms in the Collections class can be applied to a subList.

The semantics of the List returned by this method become undefined if the backing list (i.e., this List) is structurally modified in any way other than via the returned List. (Structural modifications are those that change the size of the List, or otherwise perturb it in such a fashion that iterations in progress may yield incorrect results.)

Overrides:

subList in class AbstractList

Parameters:

fromIndex - low endpoint (inclusive) of the subList

toIndex - high endpoint (exclusive) of the subList

Returns:

a view of the specified range within this List

toArray

public synchronized Object[] toArray()

Returns an array containing all of the elements in this Vector in the correct order.

Overrides:

toArray in class AbstractCollection

toArray

public synchronized Object[] toArray(Object[] a)

Returns an array containing all of the elements in this Vector in the correct order; the runtime type of the returned array is that of the specified array. If the Vector 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 Vector.

If the Vector fits in the specified array with room to spare (i.e., the array has more elements than the Vector), the element in the array immediately following the end of the Vector is set to null. (This is useful in determining the length of the Vector only if the caller knows that the Vector does not contain any null elements.)

Overrides:

toArray in class AbstractCollection

Parameters:

a - the array into which the elements of the Vector are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose.

Returns:

an array containing the elements of the Vector

toString

public synchronized String toString()

Returns a string representation of this Vector, containing the String representation of each element.

Overrides:

toString in class AbstractCollection

trimToSize

public synchronized void trimToSize()

Trims the capacity of this vector to be the vector's current size. If the capacity of this vector is larger than its current size, then the capacity is changed to equal the size by replacing its internal data array, kept in the field {@code elementData}, with a smaller one. An application can use this operation to minimize the storage of a vector.