Learning Resources

Vectors

java.util

Class Vector

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

All Implemented Interfaces:

Serializable, Cloneable, Iterable, Collection, List, RandomAccess

Direct Known Subclasses:

Stack
```
public class Vector
extends AbstractList
implements List, RandomAccess, Cloneable, Serializable
```
The Vectorclass 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 Vectorcan grow or shrink as needed to accommodate adding and removing items after the Vectorhas been created.
Each vector tries to optimize storage management by maintaining a capacityand a capacityIncrement. The capacityis 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 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 this class'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 the 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 ConcurrentModificationExceptionon 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 List interface, making it a member of the Java Collections Framework. Unlike the new collection implementations, Vectoris synchronized. If a thread-safe implementation is not needed, it is recommended to use ArrayList in place of Vector.

Since:

JDK1.0

See Also:

Collection, LinkedList, Serialized Form

Field Summary

Fields
Modifier and Type	Field and Description
`protected int`	`capacityIncrement` The amount by which the capacity of the vector is automatically incremented when its size becomes greater than its capacity.
`protected int`	`elementCount` The number of valid components in this `Vector`object.
`protected Object[]`	`elementData` The array buffer into which the components of the vector are stored.

Fields inherited from class java.util.AbstractList
modCount

Constructor Summary

Constructors
Constructor and Description
`Vector()` Constructs an empty vector so that its internal data array has size `10`and its standard capacity increment is zero.
`Vector(CollectionE> c)` Constructs a vector containing the elements of the specified collection, in the order they are returned by the collection's iterator.
`Vector(int initialCapacity)` Constructs an empty vector with the specified initial capacity and with its capacity increment equal to zero.
`Vector(int initialCapacity, int capacityIncrement)` Constructs an empty vector with the specified initial capacity and capacity increment.

Method Summary

Methods
Modifier and Type	Method and Description
`boolean`	`add(E e)` Appends the specified element to the end of this Vector.
`void`	`add(int index, E element)` Inserts the specified element at the specified position in this Vector.
`boolean`	`addAll(CollectionE> 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.
`boolean`	`addAll(int index, CollectionE> c)` Inserts all of the elements in the specified Collection into this Vector at the specified position.
`void`	`addElement(E obj)` Adds the specified component to the end of this vector, increasing its size by one.
`int`	`capacity()` Returns the current capacity of this vector.
`void`	`clear()` Removes all of the elements from this Vector.
`Object`	`clone()` Returns a clone of this vector.
`boolean`	`contains(Object o)` Returns `true`if this vector contains the specified element.
`boolean`	`containsAll(Collection c)` Returns true if this Vector contains all of the elements in the specified Collection.
`void`	`copyInto(Object[] anArray)` Copies the components of this vector into the specified array.
`E`	`elementAt(int index)` Returns the component at the specified index.
`Enumeration<E>`	`elements()` Returns an enumeration of the components of this vector.
`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.
`boolean`	`equals(Object o)` Compares the specified Object with this Vector for equality.
`E`	`firstElement()` Returns the first component (the item at index `0`) of this vector.
`E`	`get(int index)` Returns the element at the specified position in this Vector.
`int`	`hashCode()` Returns the hash code value for this Vector.
`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.
`int`	`indexOf(Object o, int index)` Returns the index of the first occurrence of the specified element in this vector, searching forwards from `index`, or returns -1 if the element is not found.
`void`	`insertElementAt(E obj, int index)` Inserts the specified object as a component in this vector at the specified `index`.
`boolean`	`isEmpty()` Tests if this vector has no components.
`Iterator<E>`	`iterator()` Returns an iterator over the elements in this list in proper sequence.
`E`	`lastElement()` Returns the last component of the vector.
`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.
`int`	`lastIndexOf(Object o, int index)` Returns the index of the last occurrence of the specified element in this vector, searching backwards from `index`, or returns -1 if the element is not found.
`ListIterator<E>`	`listIterator()` Returns a list iterator over the elements in this list (in proper sequence).
`ListIterator<E>`	`listIterator(int index)` Returns a list iterator over the elements in this list (in proper sequence), starting at the specified position in the list.
`E`	`remove(int index)` Removes the element at the specified position in this Vector.
`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.
`boolean`	`removeAll(Collection c)` Removes from this Vector all of its elements that are contained in the specified Collection.
`void`	`removeAllElements()` Removes all components from this vector and sets its size to zero.
`boolean`	`removeElement(Object obj)` Removes the first (lowest-indexed) occurrence of the argument from this vector.
`void`	`removeElementAt(int index)` Deletes the component at the specified index.
`protected void`	`removeRange(int fromIndex, int toIndex)` Removes from this list all of the elements whose index is between `fromIndex`, inclusive, and `toIndex`, exclusive.
`boolean`	`retainAll(Collection c)` Retains only the elements in this Vector that are contained in the specified Collection.
`E`	`set(int index, E element)` Replaces the element at the specified position in this Vector with the specified element.
`void`	`setElementAt(E obj, int index)` Sets the component at the specified `index`of this vector to be the specified object.
`void`	`setSize(int newSize)` Sets the size of this vector.
`int`	`size()` Returns the number of components in this vector.
`List<E>`	`subList(int fromIndex, int toIndex)` Returns a view of the portion of this List between fromIndex, inclusive, and toIndex, exclusive.
`Object[]`	`toArray()` Returns an array containing all of the elements in this Vector in the correct order.
`T[]`	`toArray(T[] 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.
`String`	`toString()` Returns a string representation of this Vector, containing the String representation of each element.
`void`	`trimToSize()` Trims the capacity of this vector to be the vector's current size.

Methods inherited from class java.lang.Object
finalize, getClass, notify, notifyAll, wait, wait, wait

- Field Detail
  - 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.
  - elementCount
```
protected int elementCount
```
    The number of valid components in this Vectorobject. Components elementData[0]through elementData[elementCount-1]are the actual items.
  - 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.
- Constructor Detail
  - 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
    
    Throws:
    
    IllegalArgumentException - if the specified initial capacity is negative
  - 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
    
    Throws:
    
    IllegalArgumentException - if the specified initial capacity is negative
  - Vector
```
public Vector()
```
    Constructs an empty vector so that its internal data array has size 10and its standard capacity increment is zero.
  - Vector
```
public Vector(CollectionE> 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
    
    Throws:
    
    NullPointerException - if the specified collection is null
    
    Since:
    
    1.2
- Method Detail
  - copyInto
```
public void copyInto(Object[] anArray)
```
    Copies the components of this vector into the specified array. The item at index kin this vector is copied into component kof anArray.
    
    Parameters:
    
    anArray - the array into which the components get copied
    
    Throws:
    
    NullPointerException - if the given array is null
    
    IndexOutOfBoundsException - if the specified array is not large enough to hold all the components of this vector
    
    ArrayStoreException - if a component of this vector is not of a runtime type that can be stored in the specified array
    
    See Also:
    
    toArray(Object[])
  - trimToSize
```
public 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 elementData, with a smaller one. An application can use this operation to minimize the storage of a vector.
  - ensureCapacity
```
public 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 minCapacity, then its capacity is increased by replacing its internal data array, kept in the field elementData, with a larger one. The size of the new data array will be the old size plus capacityIncrement, unless the value of capacityIncrementis 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 minCapacity, then the new capacity will be minCapacity.
    
    Parameters:
    
    minCapacity - the desired minimum capacity
  - setSize
```
public void setSize(int newSize)
```
    Sets the size of this vector. If the new size is greater than the current size, new nullitems are added to the end of the vector. If the new size is less than the current size, all components at index newSizeand greater are discarded.
    
    Parameters:
    
    newSize - the new size of this vector
    
    Throws:
    
    ArrayIndexOutOfBoundsException - if the new size is negative
  - capacity
```
public int capacity()
```
    Returns the current capacity of this vector.
    
    Returns:
    
    the current capacity (the length of its internal data array, kept in the field elementDataof this vector)
  - size
```
public int size()
```
    Returns the number of components in this vector.
    
    Specified by:
    
    size in interface Collection<E>
    
    Specified by:
    
    size in interface List<E>
    
    Specified by:
    
    size in class AbstractCollection<E>
    
    Returns:
    
    the number of components in this vector
  - isEmpty
```
public boolean isEmpty()
```
    Tests if this vector has no components.
    
    Specified by:
    
    isEmpty in interface Collection<E>
    
    Specified by:
    
    isEmpty in interface List<E>
    
    Overrides:
    
    isEmpty in class AbstractCollection<E>
    
    Returns:
    
    true if and only if this vector has no components, that is, its size is zero; falseotherwise.
  - elements
```
public Enumeration<E> elements()
```
    Returns an enumeration of the components of this vector. The returned Enumerationobject will generate all items in this vector. The first item generated is the item at index 0, then the item at index 1, and so on.
    
    Returns:
    
    an enumeration of the components of this vector
    
    See Also:
    
    Iterator
  - contains
```
public boolean contains(Object o)
```
    Returns trueif this vector contains the specified element. More formally, returns trueif and only if this vector contains at least one element esuch that (o==null ? e==null : o.equals(e)).
    
    Specified by:
    
    contains in interface Collection<E>
    
    Specified by:
    
    contains in interface List<E>
    
    Overrides:
    
    contains in class AbstractCollection<E>
    
    Parameters:
    
    o - element whose presence in this vector is to be tested
    
    Returns:
    
    true if this vector contains the specified element
  - 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 isuch that (o==null ? get(i)==null : o.equals(get(i))), or -1 if there is no such index.
    
    Specified by:
    
    indexOf in interface List<E>
    
    Overrides:
    
    indexOf in class AbstractList<E>
    
    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 int indexOf(Object o,
          int index)
```
    Returns the index of the first occurrence of the specified element in this vector, searching forwards from index, or returns -1 if the element is not found. More formally, returns the lowest index isuch 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 indexor later in the vector; -1if the element is not found.
    
    Throws:
    
    IndexOutOfBoundsException - if the specified index is negative
    
    See Also:
    
    Object.equals(Object)
  - lastIndexOf
```
public 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 isuch that (o==null ? get(i)==null : o.equals(get(i))), or -1 if there is no such index.
    
    Specified by:
    
    lastIndexOf in interface List<E>
    
    Overrides:
    
    lastIndexOf in class AbstractList<E>
    
    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 int lastIndexOf(Object o,
              int index)
```
    Returns the index of the last occurrence of the specified element in this vector, searching backwards from index, or returns -1 if the element is not found. More formally, returns the highest index isuch 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 indexin this vector; -1 if the element is not found.
    
    Throws:
    
    IndexOutOfBoundsException - if the specified index is greater than or equal to the current size of this vector
  - elementAt
```
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Certified Core Java Developer Learning Resources Vectors

Learning Resources

Vectors

Class Vector

Field Summary

Fields inherited from class java.util.AbstractList

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

elementData

elementCount

capacityIncrement

Constructor Detail

Vector

Vector

Vector

Vector

Method Detail

copyInto

trimToSize

ensureCapacity

setSize

capacity

size

isEmpty

elements

contains

indexOf

indexOf

lastIndexOf

lastIndexOf

elementAt

Vskills

My Account

Customer Service

Popular Links