接上篇 java集合类（一）
- List接口继承了Collection接口和Iterable接口，即同样含有Collection和 Iterable的特性，还有方法，其基本方法有：
1）有关添加： boolean add(E e):添加元素 void add(int index,E element):在特定位置添加元素
boolean addAll(Collection<? extends E> c):添加集合中所有的元素 boolean addAll(int index,Collection<? extends E> c):在特定位置添加一组元素
2）有关清除：void clear(), E remove(int index),boolean remove(Object o),boolean remove(Collection<?> c)
3）有关检验：boolean contains(Object o),boolean containAll(Collection<?> c),boolean equals(Object o),boolean isEmpty()
4）有关获取：E get(int index),int hashCode(),int indexOf(Object o),int lastIndexOf(Object o),int size(),Lisy<E> subList(int fromindex,int toindex)
5）有关设定：E set(int index, E element),boolean retainAll(Collection<?> c)
6）有关打印：Object[] toArray(), <T>T[] toArray(T[] a)
7）有关迭代：Iterator<E> iterator(),ListIterator<E> listIterator(),ListIterator<E> listIterator(int index)
8）其他：int hashcode()
List接口的实现类有很多，如：AbstractList, AbstractSequentialList, ArrayList, AttributeList, CopyOnWriteArrayList, LinkedList, RoleList,
RoleUnresolvedList, Stack, Vector，下面介绍List的几个基本实现类的用法：
- About ArrayList:
All Implemented Interfaces: Serializable, Cloneable, Iterable<E>, Collection<E>, List<E>, RandomAccess extends AbstractList
- Direct Known Subclasses: AttributeList, RoleList, RoleUnresolvedList
实例代码：
class iphone{}
public void arraylist(){
//1)Constructs an empty list with an initial capacity of ten
ArrayList al = new ArrayList();
/*
* 2)Constructs a list containing the elements of the specified
* collection, in the order they are returned by the collection's iterator
*/
ArrayList<Integer> alist = new ArrayList(Arrays.asList(1,2,3));
//3)Constructs an empty list with the specified initial capacity
ArrayList<Double> alist1 = new ArrayList(10);
al.add(new iphone());
al.add(1);
al.add("a");
al.add(alist);
System.out.println(al.hashCode()); //int hashcode()
/*
* usage of methods that aren't mentioned within "List basic methods"
*/
//ensure that list can hold at least the number of elements specified by the minimum capacity argument
alist1.ensureCapacity(30);
//Trims the capacity of this ArrayList instance to be the list's current size
alist.trimToSize();
//Returns a shallow copy of this ArrayList instance(The elements themselves are not copied)
Object o = al.clone();
}
- About LinkedList：
All Implemented Interfaces:Serializable, Cloneable, Iterable<E>, Collection<E>, Deque<E>, List<E>, Queue<E> extends AbstractSequentialList<E>
从上面可以知道，由于LinkedList实现的接口涉及到队列，所以它也会新增一些有关队列独有操作方法，还有pop(),push()等，下面举例：
public void linkedlist(){
LinkedList linklist = new LinkedList();
ArrayList<Integer> a = new ArrayList(Arrays.asList(1,2,3));
LinkedList linklist2 = new LinkedList(a);
Iterator i = linklist2.iterator();
while(i.hasNext()){
System.out.println(i.next()); //1 2 3
}
Iterator ri = linklist2.descendingIterator();
while(ri.hasNext()){
System.out.println(ri.next()); //3 2 1
}
linklist.addFirst(1);
linklist.addLast("e");
System.out.println(linklist); //[1,e]
/*linklist.getFirst();
linklist.getLast();*/
//Retrieves, but does not remove, the head (first element) of this list
System.out.println(linklist.element()); //1
linklist.offer("x");
System.out.println(linklist);//[1,e,x]
linklist.offerFirst(0);
linklist.offerLast("y");
System.out.println(linklist);//[0,1,e,x,y]
//peek..()--->[Retrieves, but does not remove]
System.out.println(linklist.peek());//0
System.out.println(linklist.peekFirst());//0 ,list is empty,return "null"
System.out.println(linklist.peekLast());//y,list is empty, return "null"
//poll..()--->[Retrieves and removes]
System.out.println(linklist.poll()); //0
System.out.println(linklist.pollFirst());//1
System.out.println(linklist.pollLast()); //y
System.out.println(linklist);//[e,x]
/*linklist.removeFirst(); //return first element
linklist.removeFirstOccurrence(Object); //boolean
linklist.removeLast(); //return last element
linklist.removeLastOccurrence(Object); //boolean
*/
System.out.println(linklist2); //[1 2 3]
//Pops an element from the stack represented by this list
System.out.println(linklist2.pop()); //1
//Pushes an element onto the stack represented by this list
linklist2.push("m");
System.out.println(linklist2);//[m,2,3]
}
- ArrayList 和LinkedList的比较：
1.ArrayList是基于动态数组，LinkedList基于链表
2.对于随机访问get和set，ArrayList觉得优于LinkedList，因为LinkedList要移动指针
3.对于新增和删除操作add和remove，LinedList比较占优势，因为ArrayList要移动数据
验证：
public void comparearraylistwithlinklist(){
SimpleDateFormat f = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
System.out.println(f.format(new Date()));
ArrayList<Integer> a = new ArrayList<Integer>();
long starttime = new Date().getTime();
for(int i = 0; i<10000; i++){
a.add(i);
}
long finishtime = new Date().getTime();
System.out.println(finishtime-starttime);
LinkedList<Integer> l = new LinkedList<Integer>();
long lstarttime = new Date().getTime();
for(int i = 0; i<10000; i++){
l.add(i);
}
long lfinishtime = new Date().getTime();
System.out.println(lfinishtime-lstarttime);
}
输出：
额外说明：以上验证代码是基于较大量数据的，输出也是不稳定的，即答案也不能确定，可能是我用错测试方法，也可能是因为数据量不够大，也可能是因为getTime（）获得的是毫秒，程序可能需要更精确的时间单位，这样才有办法比较。另外，如果对于单个数据的插入或删除，是不是LinkedList还优于ArrayList呢？答案也很明显是不一定的，读者可以按照上面的实例验证一下
由于此博文可能有点长了，其他List的学习见“java集合类（三）List学习（续）”，尽请期待！！
### 学习从来都是一个过程，对对错错对对...若文中有错误，还望读者批评指出 ###