JAVA-集合Collection初步认识：Lis…

集合存放的都是对象的引用。
Collection:
<wbr>|——List:列表，每个元素都有自己的角标，可以存入重复的元素，有序(存入的和取出的顺序一致).<br><wbr><wbr>特有方法：<br><wbr><wbr>添加：add(index, Element)<br><wbr><wbr>获取：get(index),iterator()<br><wbr><wbr>修改：set(index,Element)<br><wbr><wbr>删除：remove(index)<br><wbr><wbr>|——ArrayList:JDK1.2出现，底层使用的数组数据结构.线程不安全的，此实现不是同步的，效率高；查询速度快<br><wbr><wbr>|--Vector(少用):JDK1.0出现，1.2融合到collection中，底层页是使用数组数据结构.线程安全，实现是同步的，效率低，被ArrayList替代.查询速度快<br><wbr><wbr>|--LinkedList:底层是链表数据结构。增删速度很快，查询组度慢.<br><wbr><wbr>|--...<br><wbr>|--Set<br><wbr>|--...<br></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

import java.util.*;
class ListDemo
{
<wbr>public static void main(String[] args)<br><wbr>{<wbr><wbr><br><wbr><wbr>ArrayList lst = new ArrayList();<br><wbr><wbr><br><wbr><wbr>lst.add("abc");<br><wbr><wbr>lst.add("def");<br><wbr><wbr>lst.add("hi");</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr>lst.add(0, "hahaha");<br><wbr><wbr>lst.remove(2);<br><wbr><wbr>lst.set(1,"sx");</wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr>System.out.println("—-get方法遍历ArrayList——");<br><wbr><wbr>printList(lst);<br><wbr><wbr>System.out.println("——使用Iterator遍历ArrayList——");<br><wbr><wbr>printListByIterator(lst);</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr>//通过Enumeration接口实现ArrayList的输出.优先使用Iterator.<br><wbr><wbr>System.out.println("——使用Enumeration接口遍历ArrayList——");<br><wbr><wbr>final Iterator it = lst.iterator();<wbr> //匿名内部类访问局部成员，需要用final修饰<br><wbr><wbr>Enumeration er = new Enumeration()<br><wbr><wbr>{<br><wbr><wbr><wbr>public boolean hasMoreElements()<br><wbr><wbr><wbr>{<br><wbr><wbr><wbr><wbr>return it.hasNext();<br><wbr><wbr><wbr>}<br><wbr><wbr><wbr>public Object nextElement()<br><wbr><wbr><wbr>{<br><wbr><wbr><wbr><wbr>return it.next();<br><wbr><wbr><wbr>}<br><wbr><wbr>};<br><wbr><wbr><br><wbr><wbr>//熟悉Vector特有方法：<br><wbr><wbr>Vector v = new Vector();<br><wbr><wbr>v.addElement("a");<br><wbr><wbr>v.addElement("b");<br><wbr><wbr>v.addElement("c");<br><wbr><wbr>v.addElement("d");</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr><wbr>System.out.println("—-get方法遍历Vector——");<br><wbr><wbr>printList(v);<br><wbr><wbr>System.out.println("——使用Iterator遍历Vector——");<br><wbr><wbr>printListByIterator(v);<br><wbr><wbr>//通过Enumeration接口实现ArrayList的输出.优先使用Iterator.<br><wbr><wbr>System.out.println("——使用Enumeration遍历Vector——");<br><wbr><wbr>for (Enumeration en = v.elements(); en.hasMoreElements(); )<br><wbr><wbr>{<br><wbr><wbr><wbr>System.out.println(en.nextElement());<br><wbr><wbr>}<br><wbr><wbr><br><wbr>}</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr>public static void printListByIterator(List lst)<br><wbr>{<br><wbr><wbr>//Iterator it = lst.iterator();<wbr><wbr><br><wbr><wbr>//while(it.hasNext())<br><wbr><wbr>//{<br><wbr><wbr><wbr>//System.out.println(it.next());<br><wbr><wbr>//}<br><wbr><wbr>//迭代器更优化的写法：<br><wbr><wbr>for (Iterator it1 = lst.iterator(); it1.hasNext(); )<br><wbr><wbr>{<br><wbr><wbr><wbr>System.out.println(it1.next());<br><wbr><wbr>}<br><wbr><wbr><br><wbr><wbr>//区别：while循环，循环完成后，对象it可能需要很长的时间，才能被回收。<br><wbr><wbr><wbr><wbr> //<wbr><wbr>for循环，循环完成后，对象立即成为垃圾，被回收.</wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>

<wbr>}</wbr>

<wbr>public static void printList(List lst)<br><wbr>{<br><wbr><wbr>for (int x = 0; x &lt; lst.size(); x++)<br><wbr><wbr>{<br><wbr><wbr><wbr>System.out.println("lst["+x+"]="+lst.get(x));<br><wbr><wbr>}<br><wbr><wbr>System.out.println("size:"+lst.size());<br><wbr>}<wbr><br> }<br></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr></wbr>