ArrayListE

ArrayList<E>

java.util

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Java 1.2

cloneable serializable collection

This class is a List implementation based on an array (that is recreated as necessary as the list grows or shrinks). ArrayList implements all optional List and Collection methods and allows list elements of any type (including null ). Because ArrayList is based on an array, the get( ) and set( ) methods are very efficient. (This is not the case for the LinkedList implementation, for example.) ArrayList is a general-purpose implementation of List and is quite commonly used. ArrayList is very much like the Vector class, except that its methods are not synchronized. If you are using an ArrayList in a multithreaded environment, you should explicitly synchronize any modifications to the list, or wrap the list with Collections.synchronizedList( ) . See List and Collection for details on the methods of ArrayList . See also LinkedList .

An ArrayList has a capacity , which is the number of elements in the internal array that contains the elements of the list. When the number of elements exceeds the capacity, a new array, with a larger capacity, must be created. In addition to the List and Collection methods, ArrayList defines a couple of methods that help you manage this capacity. If you know in advance how many elements an ArrayList will contain, you can call ensureCapacity( ) , which can increase efficiency by avoiding incremental reallocation of the internal array. You can also pass an initial capacity value to the ArrayList( ) constructor. Finally, if an ArrayList has reached its final size and will not change in the future, you can call TRimToSize( ) to reallocate the internal array with a capacity that matches the list size exactly. When the ArrayList will have a long lifetime, this can be a useful technique to reduce memory usage.

Figure 16-7. java.util.ArrayList<E>

 public class  ArrayList<E>  extends AbstractList<E> implements List<E>,          RandomAccess, Cloneable, Serializable {  // Public Constructors  public  ArrayList  ( );        public  ArrayList  (int  initialCapacity  );        public  ArrayList  (Collection<? extends E>  c  );  // Public Instance Methods  public void  ensureCapacity  (int  minCapacity  );        public void  trimToSize  ( );  // Methods Implementing List  public boolean  add  (E  o  );        public void  add  (int  index  , E  element  );        public boolean  addAll  (Collection<? extends E>  c  );        public boolean  addAll  (int  index  , Collection<? extends E>  c  );        public void  clear  ( );        public boolean  contains  (Object  elem  );        public E  get  (int  index  );        public int  indexOf  (Object  elem  );        public boolean  isEmpty  ( );  default:true  public int  lastIndexOf  (Object  elem  );  5.0  public boolean  remove  (Object  o  );        public E  remove  (int  index  );        public E  set  (int  index  , E  element  );        public int  size  ( );        public Object[ ]  toArray  ( );        public <T> T[ ]  toArray  (T[ ]  a  );  // Protected Methods Overriding AbstractList  protected void  removeRange  (int  fromIndex  , int  toIndex  );  // Public Methods Overriding Object  public Object  clone  ( );   } 

Returned By

Collections.list( )