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ArrayList¾ÍÊǶ¯Ì¬Êý×飬ÓÃMSDNÖеÄ˵·¨£¬¾ÍÊÇArrayµÄ¸´ÔÓ°æ±¾£¬ËüÌṩÁ˶¯Ì¬µÄÔö¼ÓºÍ¼õÉÙÔªËØ£¬ÊµÏÖÁËCollectionºÍList½Ó¿Ú£¬¿ÉÒÔÁé»îµÄÉèÖÃÊý×éµÄ´óС¡£Òª×¢ÒâµÄÊÇArrayList²¢²»ÊÇḬ̈߳²È«µÄ£¬Òò´ËÒ»°ã½¨ÒéÔÚµ¥Ïß³ÌÖÐʹÓÃArrayList¡£
ArrayListµÄ¼Ì³Ð¹ØÏµ

public class
ArrayList<E>
extends AbstractList<E>
implements List<E>,
RandomAccess,Cloneable,Serializable |
ÓÉÉÏ¿ÉÖªArrayList¼Ì³ÐAbstractList ²¢ÇÒʵÏÖÁËListºÍRandomAccess£¬Cloneable, Serializable½Ó¿Ú¡£
ArrayListµÄ·½·¨Ê¹ÓúÍÔ´Âë½âÎö
¢Ù¹¹Ôì·½·¨
//1-----------------------
public ArrayList() {
this(10);
//µ÷ÓÃArrayList(10) ĬÈϳõʼ»¯Ò»¸ö´óСΪ10µÄobjectÊý×é¡£
}
//2-------------------------
public ArrayList (int initialCapacity) {
if (initialCapacity < 0)
throw new IllegalArgumentException ("Illegal
Capacity: "+
initialCapacity);
//Èç¹ûÓû§³õʼ»¯´óССÓÚ0Å×Òì³££¬ ·ñÔòн¨Ò»¸öÓû§³õʼֵ´óСµÄobjectÊý×é¡£
this.elementData = new Object[initialCapacity];
}
//3--------------------------
public ArrayList
(Collection< extends E> c) {
elementData = c.toArray();
size = elementData.length;
// µ±c.toArray·µ»ØµÄ ²»ÊÇobjectÀàÐ͵ÄÊý×éʱ£¬½øÐÐÏÂÃæ×ª»¯¡£
if (elementData.getClass() != Object[].class)
elementData = Arrays.copyOf (elementData, size,
Object[].class);
} |
ÓÉÉÏÃæÈýÖÖ¹¹Ôì·½·¨¿ÉÖª£¬Ä¬ÈÏÇé¿öÏÂʹÓÃArrayList»áÉú³ÉÒ»¸ö´óСΪ10µÄObjectÀàÐ͵ÄÊý×é¡£Ò²¿ÉÒÔµ÷ÓÃArrayList(int initialCapacity) À´³õʼ»¯ObjectÊý×éµÄ´óС¡£²¢ÇÒÓû§¿ÉÒÔÍùArrayListÖд«ÈëÒ»¸öÈÝÆ÷Ö»ÒªÕâ¸öÈÝÆ÷ÊÇCollectionÀàÐ͵ġ£µ÷ÓÃArrayList(Collection< extends E > c)½Ó¿ÚµÄʱºò»á½«ÈÝÆ÷Êý×黯´¦Àí²¢½«Õâ¸öÊý×éÖµ¸³¸øObjectÊý×é¡£
ʵÀý£º
public static
void main
(String[] args) {
ArrayList<Integer> list_2=new ArrayList<Integer>(20);
//list_2ÖÐÌí¼ÓÔªËØ
for(int i=0;i<10;i++)
list_2.add(i);
ArrayList<Integer> list_3=new ArrayList<Integer>(list_2);
//Êä³ölist_2ÖÐÔªËØ
for(Integer a:list_2)
System.out.print(a+" ");
//Êä³ölist_3ÖÐÔªËØ
for(Integer a:list_3)
System.out.print(a+" ");
}
//Êä³ö
/*
list_2 : 0 1 2 3 4 5 6 7 8 9
-----------------------
list_3 : 0 1 2 3 4 5 6 7 8 9
*/ |
¢ÚindexOf(Object o)·½·¨
¹¦ÄÜ£º²éÕÒij¸öÔªËØÔÚArrayListÖеÚÒ»´Î³öÏÖµÄλÖá£
public int indexOf(Object
o) {
//ArrayListÖеÄÔªËØ¿ÉÒÔΪnull£¬ Èç¹ûΪnull·µ»ØnullµÄϱê
if (o == null) {
for (int i = 0; i < size; i++)
if (elementData[i]==null)
return i;
} else {
for (int i = 0; i < size; i++)
if (o.equals(elementData[i]))
return i;
}
//Èç¹ûûÓÐÕÒµ½¶ÔÓ¦µÄÔªËØ·µ»Ø-1¡£
return -1;
} |
¶ÔÓÚindexof·½·¨×ö¼¸µã˵Ã÷£ºArrayListÖпÉÒÔ´æ·ÅnullÔªËØ£¬indexofÊÇ·µ»ØelementDataÊý×éÖÐÖµÏàͬµÄÊ׸öÔªËØµÄϱ꣬indexofÖбȽϷ½·¨ÊÇequals¶øequalsÊDZȽÏÔªËØµÄÖµ£¬Òò´Ë±ØÐë¶Ônullµ¥¶À²éÕÒ¡£Èç¹ûδÕÒµ½¸ÃÔªËØÔò·µ»Ø-1 ¡£
public static
void main
(String[] args) {
ArrayList<Integer> list=new ArrayList<Integer>();
list.add(1);
list.add(2);
list.add(null);
list.add(2);
list.add(3);
System.out.println ("null: "+list.indexOf(null));
System.out.println ("-------------------------");
System.out.println ("2: "+list.indexOf(2));
System.out.println ("-------------------------");
System.out.println ("4: "+list.indexOf(4));
}
//Êä³ö
/*
null: 2
-------------------------
2: 1
-------------------------
4: -1
*/ |
¢ÛlastIndexOf(Object o)·½·¨
¹¦ÄÜ£º²éÕÒij¸öÔªËØÔÚArrayListÖÐ×îºó³öÏÖµÄλÖá£
public int lastIndexOf (Object
o) {
if (o == null) {
//Èç¹ûoΪnull´ÓºóÍù ǰÕÒµ½µÚÒ»¸öΪnullµÄϱê
for (int i = size-1; i >= 0; i--)
if (elementData[i]==null)
return i;
} else {
//´ÓºóÍùǰÕÒµ½µÚÒ»¸öֵΪoµÄϱê
for (int i = size-1; i >= 0; i--)
if (o.equals(elementData[i]))
return i;
}
return -1;
} |
ÉÏÃæ´úÂë×ö¼¸µã˵Ã÷£ºlastIndexOf(Object o)ÔÚArrayListÖдӺóÍùǰÕÒµ½µÚÒ»¸ö¸úÒª²éÕÒÖµÏàͬµÄÔªËØµÄϱ꣬ÒòΪÊǰ´Öµ²éÕÒËùÒÔ¶ÔÓÚ null Òªµ¥¶À²éÕÒ¡£Èç¹ûδÕÒµ½Ôò·µ»Ø-1£»
¢Üget(int index)·½·¨
¹¦ÄÜ£º·µ»ØArrayListÖÐÖ¸¶¨Ï±êΪindexµÄÔªËØ¡£
public E get(int
index) {
//¼ì²éindexµÄÖµÊÇ·ñ´óÓÚArrayListµÄ´óС
rangeCheck(index);
//·µ»ØindexϱêµÄÔªËØ
return elementData(index);
}
E elementData(int index) {
return (E) elementData[index];
}
//ÕâÀïÖµ¼ì²éindex >= sizeµÄÇé¿ö£¬ ÒòΪindex<0ʱ»á×Ô¶¯Å׳öÒì³££¬ ËùÒÔ²¢Î´¼ì²éindex<0µÄÇé¿ö¡£
private void rangeCheck (int index) {
if (index >= size)
throw new IndexOutOfBoundsException (outOfBoundsMsg(index));
} |
¶ÔÉÏÃæ´úÂë×ö¼¸µã˵Ã÷£ºÉÏÃæ´úÂëÖÐÖ»¼ì²éÁËindex>=sizeµÄÇé¿ö£¬ÔÚindex< 0µÄÇé¿öÏÂÒ²»áÅ׳öÒì³££¬Ö»ÊÇÕâ¸öÒì³£ÊÇÓÉϵͳÅ׳öµÄ¡£index >=sizeÒª¼ì²éµÄÔÒòÊÇÓпÉÄÜÊý×éµÄ´óС´óÓÚindex£¬È»¶øÓÐЧÀïÃæµÄÔªËØ< indexÕâʱ²»Å×Òì³£¾Í»á·µ»ØÎÞЧֵ¡£¾Ù¸öÀý×ÓArrayListµÄ³õʼ»¯´óСΪ10£¬ÏÖÔÚÍùÀïÃæ·Å5¸öÔªËØ£¬Èç¹ûindex >=5ʱ£¬Ó¦¸ÃÒªÅ׳öÒì³££¬¶ø²»ÊÇ·µ»Ø null¡£ÒòΪnull ÊÇ¿ÉÒÔÖ÷¶¯·ÅÔÚArrayListÖеġ£
¢Ýset(int index, E element)·½·¨
¹¦ÄÜ£º½«element·Åµ½ArrayListϱêΪindexµÄλÖã¬Èç¹ûindex< 0»òindex >=size Å×Òì³££¬set(int index, E element)Ö»Äܸ²¸ÇArrayListÖÐÔÀ´µÄÔªËØ£¬·µ»ØÖµÎª±»¸²¸ÇµÄÔªËØ¡£
//1
public E set(int index, E element) {
//¼ì²éindexÊÇ·ñСÓÚsize£¬Èç¹û²»ÊÇÅ×Òì³£
rangeCheck(index);
E oldValue = elementData(index);
elementData[index] = element;
//¸²¸ÇArrayListÖÐindexÉϵÄÔªËØ¡£
return oldValue;
//·µ»Ø±»¸²¸ÇµÄÔªËØ¡£
}
//2
private void rangeCheck (int index) {
if (index >= size)
throw new IndexOutOfBoundsException (outOfBoundsMsg(index));
} |
¢Þadd(E e)·½·¨
¹¦ÄÜ£ºÍùArrayListÖÐÌí¼ÓÔªËØ¡£
//1-----------------------
public boolean add(E e) {
ensureCapacityInternal(size + 1); // ¼ÓÈëÔªËØÇ°¼ì²éÊý×éµÄÈÝÁ¿ÊÇ·ñ×ã¹»
elementData[size++] = e;
return true;
}
//2-----------------------
private void ensureCapacityInternal (int minCapacity)
{
modCount++;
// Èç¹ûÌí¼ÓÔªËØºó´óÓÚ µ±Ç°Êý×éµÄ³¤¶È£¬Ôò½øÐÐÀ©ÈÝ
if (minCapacity - elementData.length > 0)
grow(minCapacity);
}
//3-----------------------
private void grow(int minCapacity) {
// overflow-conscious code
int oldCapacity = elementData.length;
//½«Êý×éµÄ³¤¶ÈÔö¼ÓÔÀ´Êý×éµÄÒ»°ë¡£
int newCapacity = oldCapacity + (oldCapacity >>
1);
if (newCapacity - minCapacity < 0)
newCapacity = minCapacity;
//Èç¹ûÀ©³äÒ»°ëºóÈÔÈ»²»¹»,ÔònewCapacity= minCapacity;minCapacityʵ¼ÊÔªËØµÄ¸öÊý¡£
if (newCapacity - MAX_ARRAY_SIZE > 0)
newCapacity = hugeCapacity(minCapacity);
//Êý×é×î´óλ2^32
// minCapacity is usually close to size, so this
is a win:
elementData = Arrays.copyOf (elementData, newCapacity);
} |
add·½·¨±È½Ï¸´ÔÓ£¬Éæ¼°µ½À©³äÊý×éÈÝÁ¿µÄÎÊÌâ¡£ÆäÖÐҪŪÇå³þsizeºÍelementData.lengthµÄÇø±ð£¬sizeÖ¸µÄÊÇÊý×éÖдæ·ÅÔªËØµÄ¸öÊý£¬elementData.length±íʾÊý×éµÄ³¤¶È£¬µ±newÒ»¸öArrayListϵͳĬÈϲúÉúÒ»¸ö³¤¶ÈΪ10µÄelementDataÊý×飬elementData.length=10£¬µ«ÊÇÓÉÓÚelementDataÖл¹Î´·ÅÈκÎÔªËØËùÓÐsize=0¡£Èç¹û¼ÓÈëÔªËØºóÊý×é´óС²»¹»»áÏȽøÐÐÀ©ÈÝ£¬Ã¿´ÎÀ©Èݶ¼½«Êý×é´óСÔö´óÒ»°ë±ÈÈçÊý×é´óСΪ10Ò»´ÎÀ©ÈݺóµÄ´óСΪ10+5=10;ArrayListµÄ×î´ó³¤¶ÈΪ 2^32 .
¢ßadd(int index, E element)·½·¨
¹¦ÄÜ£ºÍùArrayListÖ¸¶¨indexÉÏÌí¼ÓÔªËØ£¬Ìí¼ÓÔªËØºóArrayListµÄ´óСÔö1¡£index¼°ÒÔºóµÄÔªËØ¶¼»áÏòºóÒÆÒ»Î»¡£
//1-------------------------
public void add (int index, E element) {
rangeCheckForAdd(index);
//¼ì²éindexµÄÖµÊÇ·ñ ÔÚ0µ½sizeÖ®¼ä£¬¿ÉÒÔΪsize¡£
ensureCapacityInternal(size + 1); // ¿´elementDataµÄ³¤¶ÈÊÇ·ñ×ã¹»£¬ ²»¹»À©ÈÝ
//½«elementData´Óindex ¿ªÊ¼ºóÃæµÄÔªËØÍùºóÒÆÒ»Î»¡£
System.arraycopy(elementData, index, elementData,
index + 1,
size - index);
elementData[index] = element;
size++;
}
//2-------------------------
private void rangeCheckForAdd (int index) {
if (index > size || index < 0)
throw new IndexOutOfBoundsException (outOfBoundsMsg(index));
}
//3-------------------------
private void ensureCapacityInternal (int minCapacity)
{
modCount++;
// overflow-conscious code
if (minCapacity - elementData.length > 0)
grow(minCapacity);
} |
add(int index, E element)ÍùÖ¸¶¨indexÖмÓÈëÔªËØ£¬¼ÓÈëÔªËØÖ®Ç°Ïȼì²éÊý×éµÄ´óС£¬Èç¹ûСÁËÔÚÔÀ´»ù´¡ÉÏÔö´óÒ»°ë£¬½«ArrayListÖ»ÄܹÖindex¼°ÒÔºóµÄÔªËØÍùºóÒÆÒ»Î»£¬½«element·Åµ½indexλÖá£
¢àremove(int index)·½·¨
¹¦ÄÜ£ºÉ¾³ýArrayListÖ¸¶¨Î»ÖõÄÔªËØ¡£
public E remove(int
index) {
rangeCheck(index);
//Èç¹ûindex>=sizeÅ׳öÒì³£
modCount++;
E oldValue = elementData(index);
//»ñȡɾ³ýÔªËØµÄÖµ
int numMoved = size - index - 1;
//½«indexºóÃæËùÓеÄÔªËØÍùÇ°ÒÆÒ»Î»¡£
if (numMoved > 0)
System.arraycopy(elementData, index+1, elementData,
index,
numMoved);
elementData[--size] = null; // Let gc do its work
//·µ»ØÒªÉ¾³ýµÄÔÊý¡£
return oldValue;
} |
¢áremove(Object o)·½·¨
¹¦ÄÜ£ºÉ¾³ýArrayListÖÐֵΪoµÄÔªËØ
public boolean
remove
(Object o) {
if (o == null) {
for (int index = 0; index < size; index++)
if (elementData[index]==null){
fastRemove(index);
return true;
}
} else {
for (int index = 0; index < size; index++)
if (o.equals (elementData[index])) {
fastRemove(index);
return true;
}
}
return false;
} |
|