java集合源碼分析

List，Set，Map都是接口，前兩個繼承Collection接口，Map爲獨立接口
Set的實現由HashSet，LinkedHashSet，TreeSet
List下有ArrayList，Vector，LinkedList
Map下有Hashtable，LinkedHashMap，HashMap，TreeMap
Collection還有Queue接口，實現有PriorityQueue

ArrayList、LinkedList、HashMap中都有字段叫modCount，字段用途：
/**

• The number of times this list has been <i>structurally modified</i>.
• 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.
• <p>This field is used by the iterator and list iterator implementation
• returned by the {@code iterator} and {@code listIterator} methods.
• If the value of this field changes unexpectedly, the iterator (or list
• iterator) will throw a {@code ConcurrentModificationException} in
• response to the {@code next}, {@code remove}, {@code previous},
• {@code set} or {@code add} operations. This provides
• <i>fail-fast</i> behavior, rather than non-deterministic behavior in
• the face of concurrent modification during iteration.
• <p><b>Use of this field by subclasses is optional.</b> If a subclass
• wishes to provide fail-fast iterators (and list iterators), then it
• merely has to increment this field in its {@code add(int, E)} and
• {@code remove(int)} methods (and any other methods that it overrides
• that result in structural modifications to the list). A single call to
• {@code add(int, E)} or {@code remove(int)} must add no more than
• one to this field, or the iterators (and list iterators) will throw
• bogus {@code ConcurrentModificationExceptions}. If an implementation
• does not wish to provide fail-fast iterators, this field may be
• ignored.
  */

*
此列表在結構上被修改的次數。
結構修改是指改變
列出，或者以這樣一種方式干擾它
進度可能會產生不正確的結果。

<p>此字段由迭代器和列表迭代器實現使用
由@code迭代器和@code lis迭代器方法返回。
如果此字段的值意外更改，則迭代器（或列表
迭代器）將在
響應@code next，@code remove，@code previous，
@code set或@code add操作。這提供了
<i>fail fast</i>behavior，than non determinatic behavior in
迭代期間併發修改的面。

<p><b>按子類使用此字段是可選的。<b>如果是子類
希望提供fail-fast迭代器（和list迭代器），然後
只需在其@code add（int，e）中增加該字段，
@code remove（int）方法（以及它重寫的任何其他方法）
這將導致對列表進行結構修改）。打個電話給
@code add（int，e）或@code remove（int）必須添加不超過
一個到這個字段，或者迭代器（和列表迭代器）將拋出
僞造{@code ConcurrentModificationExceptions}。如果一個實現
不希望提供fail-fast迭代器，此字段可能是
已忽略。
/

List<String> list=new ArrayList();
list.add("config");
list.add("config");
list.add("config1");
list.add("config");
list.add("config");
list.add("config");
list.add("config");
list.add("config");
list.add("config");
list.add("config");
list.add("config");
list.forEach(s -> {
if("config1".equals(s)){
list.remove(s);
}
});

java.util.ConcurrentModificationException
at java.util.ArrayList.forEach(ArrayList.java:1260)
at com.mufeng.test.base.dataStructure.TestList.test1(TestList.java:31)

//HashSet
//巧妙利用HashMap中key實現

private transient HashMap<E,Object> map;
// Dummy value to associate with an Object in the backing Map
// 仿真的值與Map中對象保持一致
private static final Object PRESENT = new Object();
public HashSet() {
map = new HashMap<>();
}

public boolean add(E e) {
return map.put(e, PRESENT)==null;
}

public boolean remove(Object o) {
return map.remove(o)==PRESENT;
}

//LinkedHashSet
//繼承HashSet
public class LinkedHashSet<E>
extends HashSet<E>
implements Set<E>, Cloneable, java.io.Serializable {

//初始容量爲16
public LinkedHashSet() {
super(16, .75f, true);
}

//LinkedHashMap
//繼承HashMap 好多方法都可以用HashMap中的
public class LinkedHashMap<K,V>
extends HashMap<K,V>
implements Map<K,V>

static class Entry<K,V> extends HashMap.Node<K,V> {
Entry<K,V> before, after;
Entry(int hash, K key, V value, Node<K,V> next) {
super(hash, key, value, next);
}
}

/**
 * The head (eldest) of the doubly linked list.
 */
 //單鏈表 首位
transient LinkedHashMap.Entry<K,V> head;

/**
 * The tail (youngest) of the doubly linked list.
 */
 //末位
transient LinkedHashMap.Entry<K,V> tail;

/**
 * The iteration ordering method for this linked hash map: <tt>true</tt>
 * for access-order, <tt>false</tt> for insertion-order.
 *
 * @serial
 */
final boolean accessOrder;

//TreeSet
//具體實現爲TreeMap
private transient NavigableMap<E,Object> m;

// Dummy value to associate with an Object in the backing Map
//仿真值
private static final Object PRESENT = new Object();

public TreeSet() {
    this(new TreeMap<E,Object>());
}
//利用TreeMap的key
public boolean add(E e) {
    return m.put(e, PRESENT)==null;
}

public boolean remove(Object o) {
    return m.remove(o)==PRESENT;
}