Java集合類原始碼(粒度：方法層面)
ArrayList
構造方法，有三種
public ArrayList(int initialCapacity)
/*
初始化容量>0,分配空間
初始化容量=0，賦值空陣列
否則拋IllegalArgumentException異常
*/
public ArrayList() //直接賦值空陣列
public ArrayList(Collection<? extends E> c)
/*
對於集合C,若集合不為空，將C賦給底層陣列，否則賦值空陣列。
*/
其他方法
public void trimToSize() //將陣列的空餘位置全剪掉
public void ensureCapacity(int minCapacity)
//判斷是否容量是否大於等於minCapacity，否則擴容
private static int calculateCapacity(Object[] elementData, int minCapacity)
//計算陣列的容量(預設為10),返回max(10,minCapacity)
private void ensureCapacityInternal(int minCapacity)
private void ensureExplicitCapacity(int minCapacity)
//以上三個函式配套，判斷當前陣列容量>=minCapacity,否則擴容
private void grow(int minCapacity)
//擴容，將原來容量擴到1.5倍，取與minCapacity的較大值，不超過INT.MAX_VALUE
private static int hugeCapacity(int minCapacity)
/*
判斷minCapacity<0,小於0證明溢位了，報錯。
比較minCapacity與MAX_ARRAY_SIZE的大小，
如果比MAX_ARRAY_SIZE大，則返回int的最大值，否則返回MAX_ARRAY_SIZE
*/
public int size() //返回當前陣列包含的元素個數
public boolean isEmpty()//判空
public boolean contains(Object o)//判斷list是否存在元素o
public int indexOf(Object o) //返回元素o出現的第一個位置，沒出現返回-1
public int lastIndexOf(Object o)返回元素o出現的最後一個位置，沒出現返回-1
public Object clone()//返回陣列的淺複製
public Object[] toArray()//返回list的靜態陣列
其他的，增刪有操作一個元素，有操作多個元素。
刪除具有快速失敗機制，發現modCount和之前不對，就返回刪除失敗，
清空陣列，
實現迭代器Iterator功能，
序列化。
HashMap
成員變數
static final int DEFAULT_INITIAL_CAPACITY = 1 << 4; // 預設容量
static final int MAXIMUM_CAPACITY = 1 << 30;//最大容量
static final float DEFAULT_LOAD_FACTOR = 0.75f;//負載因子，當佔用空間超過容量的這個比例就會擴容
static final int TREEIFY_THRESHOLD = 8;//節點樹化閾值，（插入後）連結串列節點數大於這個值則樹化
static final int UNTREEIFY_THRESHOLD = 6;//退化成連結串列的閾值
static final int MIN_TREEIFY_CAPACITY = 64;//節點樹化的條件之一：要滿足整體容量>=64
transient Node<K,V>[] table;//底層陣列
transient Set<Map.Entry<K,V>> entrySet;
final float loadFactor;//負載因子
transient int modCount;
transient int size;
int threshold;//當map元素個數達到threshold個，發生擴容
重點方法
- 新增元素putval
//所有的新增，最後都是走這裡
/*
hash:key的hash值
onlyIfAbsent :true的話，不替代原有元素，false替換
evict：false表示剛建立map時新增初始元素，true表示建map後新增新元素
*/
final V putVal(int hash, K key, V value, boolean onlyIfAbsent,
boolean evict) {
Node<K,V>[] tab; Node<K,V> p; int n, i;
//判斷tab為空
if ((tab = table) == null || (n = tab.length) == 0)
n = (tab = resize()).length;//擴容
//i儲存在tab陣列下標位置，下面判斷到該位置沒有被佔
if ((p = tab[i = (n - 1) & hash]) == null)
tab[i] = newNode(hash, key, value, null);
else {
Node<K,V> e; K k;
//如果當前位置的key相同，替換
if (p.hash == hash &&
((k = p.key) == key || (key != null && key.equals(k))))
e = p;
//如果是樹化節點，就遍歷樹，找到合適位置插入
else if (p instanceof TreeNode)
e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value);
//普通連結串列節點
else {
for (int binCount = 0; ; ++binCount) {
if ((e = p.next) == null) {
p.next = newNode(hash, key, value, null);
//如果該條鏈已經大於等於8個了，樹化
if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st
treeifyBin(tab, hash);
break;
}
//找到相同key的鍵值對
if (e.hash == hash &&
((k = e.key) == key || (key != null && key.equals(k))))
break;
p = e;
}
}
if (e != null) { // existing mapping for key
V oldValue = e.value;
if (!onlyIfAbsent || oldValue == null)
e.value = value;
afterNodeAccess(e);
return oldValue;
}
}
++modCount;
if (++size > threshold)
resize();
afterNodeInsertion(evict);
return null;
}
- 擴容resize
final Node<K,V>[] resize() {
Node<K,V>[] oldTab = table;
int oldCap = (oldTab == null) ? 0 : oldTab.length;//陣列容量
int oldThr = threshold;//當前陣列元素個數
int newCap, newThr = 0;
if (oldCap > 0) {
//達到最大，擴不了，將threshold調到最大，能裝多少就裝多少
if (oldCap >= MAXIMUM_CAPACITY) {
threshold = Integer.MAX_VALUE;
return oldTab;
}
else if ((newCap = oldCap << 1) < MAXIMUM_CAPACITY &&
oldCap >= DEFAULT_INITIAL_CAPACITY)
//擴容到原來的兩倍
newThr = oldThr << 1; // double threshold
}
else if (oldThr > 0) // initial capacity was placed in threshold
newCap = oldThr;
else { // zero initial threshold signifies using defaults
newCap = DEFAULT_INITIAL_CAPACITY;
newThr = (int)(DEFAULT_LOAD_FACTOR * DEFAULT_INITIAL_CAPACITY);
}
if (newThr == 0) {
float ft = (float)newCap * loadFactor;
newThr = (newCap < MAXIMUM_CAPACITY && ft < (float)MAXIMUM_CAPACITY ?
(int)ft : Integer.MAX_VALUE);
}
threshold = newThr;
@SuppressWarnings({"rawtypes","unchecked"})
Node<K,V>[] newTab = (Node<K,V>[])new Node[newCap];
table = newTab;
//重新放置原來的元素，
/*
對於連結串列或紅黑樹，將它們分成兩條鏈，低位鏈和高位鏈，再根據鏈長度選擇樹化，最後接到陣列位置。
*/
if (oldTab != null) {
for (int j = 0; j < oldCap; ++j) {
Node<K,V> e;
if ((e = oldTab[j]) != null) {
oldTab[j] = null;
//只有一個節點
if (e.next == null)
newTab[e.hash & (newCap - 1)] = e;
//樹
else if (e instanceof TreeNode)
((TreeNode<K,V>)e).split(this, newTab, j, oldCap);
//連結串列
else { // preserve order
Node<K,V> loHead = null, loTail = null;//低位鏈
Node<K,V> hiHead = null, hiTail = null;//高位鏈
Node<K,V> next;
do {
next = e.next;
if ((e.hash & oldCap) == 0) {
if (loTail == null)
loHead = e;
else
loTail.next = e;
loTail = e;
}
else {
if (hiTail == null)
hiHead = e;
else
hiTail.next = e;
hiTail = e;
}
} while ((e = next) != null);
if (loTail != null) {
loTail.next = null;
newTab[j] = loHead;
}
if (hiTail != null) {
hiTail.next = null;
newTab[j + oldCap] = hiHead;
}
}
}
}
}
return newTab;
}
- 樹節點的Split方法，用來擴容時重新分位置。可以看到和上面連結串列的分鏈一模一樣。
final void split(HashMap<K,V> map, Node<K,V>[] tab, int index, int bit) {
TreeNode<K,V> b = this;
// Relink into lo and hi lists, preserving order
TreeNode<K,V> loHead = null, loTail = null;
TreeNode<K,V> hiHead = null, hiTail = null;
int lc = 0, hc = 0;
for (TreeNode<K,V> e = b, next; e != null; e = next) {
next = (TreeNode<K,V>)e.next;
e.next = null;
if ((e.hash & bit) == 0) {
if ((e.prev = loTail) == null)
loHead = e;
else
loTail.next = e;
loTail = e;
++lc;
}
else {
if ((e.prev = hiTail) == null)
hiHead = e;
else
hiTail.next = e;
hiTail = e;
++hc;
}
}
/*
和連結串列分鏈的唯一區別是判斷是否要樹化或反樹化
*/
if (loHead != null) {
if (lc <= UNTREEIFY_THRESHOLD)
tab[index] = loHead.untreeify(map);
else {
tab[index] = loHead;
if (hiHead != null) // (else is already treeified)
loHead.treeify(tab);
}
}
if (hiHead != null) {
if (hc <= UNTREEIFY_THRESHOLD)
tab[index + bit] = hiHead.untreeify(map);
else {
tab[index + bit] = hiHead;
if (loHead != null)
hiHead.treeify(tab);
}
}
}
- 節點樹化 treeify，將連結串列建成紅黑樹
final void treeify(Node<K,V>[] tab) {
TreeNode<K,V> root = null;
for (TreeNode<K,V> x = this, next; x != null; x = next) {
next = (TreeNode<K,V>)x.next;
x.left = x.right = null;
if (root == null) {
x.parent = null;
x.red = false;//根節點是黑色的
root = x;
}
else {
K k = x.key;
int h = x.hash;
Class<?> kc = null;
for (TreeNode<K,V> p = root;;) {
int dir, ph;
K pk = p.key;
if ((ph = p.hash) > h)
dir = -1;
else if (ph < h)
dir = 1;
else if ((kc == null &&
(kc = comparableClassFor(k)) == null) ||
(dir = compareComparables(kc, k, pk)) == 0)
dir = tieBreakOrder(k, pk);
TreeNode<K,V> xp = p;
if ((p = (dir <= 0) ? p.left : p.right) == null) {
x.parent = xp;
if (dir <= 0)
xp.left = x;
else
xp.right = x;
root = balanceInsertion(root, x);
break;
}
}
}
}
moveRootToFront(tab, root);
}
- 反樹化untreeify，就是將treeNode變回Node，化鏈。
final Node<K,V> untreeify(HashMap<K,V> map) {
Node<K,V> hd = null, tl = null;
for (Node<K,V> q = this; q != null; q = q.next) {
Node<K,V> p = map.replacementNode(q, null);
if (tl == null)
hd = p;
else
tl.next = p;
tl = p;
}
return hd;
}