Java Collection Framework 学习笔记

1. Use Iterator instead of the for-each construct when you need to:

a. Remove the current element. The for-each construct hides the iterator, so you cannot call remove. Therefore, the for-each construct is not usable for filtering.
b. Iterate over multiple collections in parallel.

for (Iterator<String> i = c.iterator(); i.hasNext(); )
      if (i.next().length() == 4)
        i.remove();

 

 2. bulk operation

a. removeAll()

c.removeAll(Collections.singleton(e));

More specifically, suppose you want to remove all of the null elements from a Collection.

c.removeAll(Collections.singleton(null));

 

3. Map Interface

a. Comparison to Hashtable 

Map provides Collection views instead of direct support for iteration via Enumeration objects. Collection views greatly enhance the expressiveness of the interface, as discussed later in this section.

Map allows you to iterate over keys, values, or key-value pairs; Hashtable does not provide the third option.

Map provides a safe way to remove entries in the midst of iteration; Hashtable did not.

Hashtable has method contains, but Map has containsValue parallels containsKey.

 

4. Implementations

 

General-purpose Implementations Interfaces Hash table Implementations Resizable array Implementations Tree Implementations Linked list Implementations Hash table + Linked list Implementations

Set	HashSet		TreeSet		LinkedHashSet
List		ArrayList		LinkedList
Queue
Map	HashMap		TreeMap		LinkedHashMap

 

Queue implementation include LinkedList and PriorityQueue.

 

5. Convenience Implementations

a. Arrays.asList

b. Immutable Multiple-Copy List

    Collections.nCopies

c. Immutable Singleton Set

    Collections.singleton

d.Empty Set, List, and Map Constants

    The Collections.emptySet, Collections.emptyList, and Collections.emptyMap.