java.util.Collection

  • List
  • Set
  • SortedSet
  • NavigableSet
  • Queue
  • Deque

image.png

  1.    /**
  2.      * Returns the number of elements in this collection.  If this collection
  3.      * contains more than <tt>Integer.MAX_VALUE</tt> elements, returns
  4.      * <tt>Integer.MAX_VALUE</tt>.
  5.      *
  6.      * @return the number of elements in this collection
  7.      */
  8.     int size(); size最大大小Integer.MAX_VALUE

HashSet有序？
HashSet底层是HashMap 值是new Object();

  1.     static final int hash(Object key) {
  2.         int h;
  3.         return (key == null) ? 0 : (h = key.hashCode()) ^ (h >>> 16);
  4.     }
  5.     public int hashCode() {
  6.         int h = hash;
  7.         if (h == 0 && value.length > 0) {
  8.             char val[] = value;
  10.             for (int i = 0; i < value.length; i++) {
  11.                 h = 31 * h + val[i];
  12.             }
  13.             hash = h;
  14.         }
  15.         return h;
  16.     }

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  1. LinkedList list = new LinkedList();
  2. Queue queue = new LinkedList();
  3. Deque deque = new LinkedList();

java.util.concurrent.BlockingQueue
java.util.concurrent.BlockingDeque
java.util.concurrent.TransferQueue

https://www.jrebel.com/blog/java-collections-cheat-sheet

java.util.HashMap

遗留实现

  • Vector

数组实现，线程安全

  • Stack
  • Hashtable

key value都不允许null

  • Enumeration

StringTokenizer

  • BitSet

image.png

抽象实现

AbstractCollection
AbstractList

面试题

DeepCloneDemo

Collection是单纬度数据集合
Map是二维数据集合

Java集合遍历实现

  • java.util.Collections
  • java.util.Arrays

Collections.jpg
Objects.png

不变集合

Collections.SingletonList();
singletonMap
singletonList

不变数组

需要深拷贝

空集合接口

  • Collections.emptyEnumeration()
  • Collections.emptyIterator()

  • Collections.emptyListIterator()

    转换接口

  • List Collections.list(Enumeration) Arrays.asList(T …)

  • Set Collections.newSetFromMap
  • Queue Collections.asLifoQueue(Deque)
  • HashCode Arrays.hashCode()

  • String Arrays.toString

    列举集合

  • BitSet.valueOf

  • EnumSet.valueOf
  • Stream.of

  • Set.of Since Java9

    包装实现

  • Collections.synchronized*

  • Collections.unmodifiable*
  • Collections.checked*

集合特殊实现

  • WeakHashMap
  • ThreadLocal.ThreadLocalMap
  • IdentityHashMap
  • PriorityQueue
  • EnumSet