全新java初学者实践教程10(java SE5.0版)
id2j7|$, jdk5的集合类
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F)'.g d &i$ldR Stu4t==U 上次课我们学过了数组,知道它只是一组数(或是对象),但是有些自己的特性。在[font="Times]java里还有一类东西与数组类似,也是有着特性的一组数[font="Times](或是对象[font="Times]),叫做集合类。
\uza=e 我们上节课讲到了,数组的长度在创建时已经确定了,但是有时候我们事先根本不知道长度是多少啊,比如我们做电子商务网站时,有个购物车程序。你总不能用数组规定,人家只能买[font="Times]5样东西吧。你就是把长度定为[font="Times]10000也不行,万一遇上个特别有钱的呢!呵呵,这只是开玩笑的。我们会使用集合类解决这个问题。
t3&LO~Ye [font="Times] 集合类是放在[font="Times]java.util.*;这个包里。集合类存放的都是对象的引用,而非对象本身,为了说起来方便些,我们称集合中的对象就是指集合中对象的引用([font="Times]reference)。引用的概念大家不会忘了吧,在前边我们讲
数据类型时讲的。
Ljx(\Cm 4<lRPsvgc [font="Times] 集合类型主要有[font="Times]3种:[font="Times]set(集)、[font="Times]list(列表)、[font="Times]map(映射[font="Times])和[font="Times]Queue(队列)。[font="Times]//队列为[font="Times]jdk5中的加上的[font="Times]
ucG@?@JENm Y}#J4i0b* [font="Times](1) Set
d;>#Sxf 集([font="Times]set)是最简单的一种集合,它的对象不按特定方式排序,只是简单的把对象加入集合中,就像往口袋里放东西。对集中成员的访问和操作是通过集中对象的引用进行的,所以集中不能有重复对象。我们知道数学上的集合也是[font="Times]Set这个,集合里面一定是没有重复的元素的。
,^eYlmT>6 \ywXi~+kUv ([font="Times]2)[font="Times]List
VrxQc qPr` 列表([font="Times]List)的主要特征是其对象以线性方式存储,没有特定顺序,只有一个开头和一个结尾,当然,它与根本没有顺序的[font="Times]Set是不同的。它是链表嘛,一条链肯定有顺序这个顺序就不一定了。
2-C!jAfd wv\w;' L;'"A#Pa [font="Times] ([font="Times]3)[font="Times]Map
]y1OFKYv [font="Times] 映射([font="Times]Map),这个在[font="Times]java里不是地图的意思,其实地图也是映射哈。它里面的东西是键-值对([font="Times]key-value)出现的,键值对是什么呢?举个例子,比如我们查字典,用部首查字法。目录那个字就是键,这个字的解释就是值。键和值成对出现。这样说可以理解吧。这也是很常用的数据结构哦。
Vp3ZwS h3z{(-~y \<y#R~7s [font="Times] ([font="Times]4)[font="Times]Queue
@AIaC-,~] [font="Times] 在[font="Times]jdk5.0以前,通常的实现方式是使用[font="Times]java.util.List集合来模仿[font="Times]Queue。[font="Times]Queue的概念通过把对象添加(称为[font="Times]enqueuing的操作)到[font="Times]List的尾部(即[font="Times]Queue的后部)并通过从[font="Times]List的头部(即[font="Times]Queue的前部)提取对象而从[font="Times] List中移除(称为[font="Times]dequeuing的操作)来模拟。你需要执行先进先出的动作时可以直接使用[font="Times]Queue接口就可以了。
M>i9 i-dU [font="Times] 这[font="Times]4个东西,有时候功能还不太完善,需要有些子类继承它的特性。[font="Times]Set的子接口有[font="Times]TreeSet,SortedSet,[font="Times]List的有[font="Times]ArrayList等,[font="Times]Map里有[font="Times]HashMap,HashTable等,[font="Times]Queue里面有[font="Times]BlockingQueue等。我们来看看例子吧:
>76\nGO VBcy9|lD :"xzj<( 实践:[font="Times] Set举例
bqnNLs<N [font="Times] import java.util.*;
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!m2Gg [font="Times]public class SetExample {
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ihAU" [font="Times] public static void main(String[] args) {
/p+>NZ"b [font="Times] Set set = new HashSet(); //HashSet是[font="Times]Set的子接口
~1W x= [font="Times] set.add("one");
}}>q2y [font="Times] set.add("second");
32/MkuY^u [font="Times] set.add("3rd");
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_t [font="Times] set.add(new Integer(4));
K%F,='P} [font="Times] set.add(new Float( 5.0F ));
$0lD>yu [font="Times] set.add("second");
MBhWMCN2 [font="Times] set.add(new Integer(4));
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[font="Times] System.out.println(set);
OVhE??# [font="Times] }}
9/ibWa\. \8?Tdx= [font="Times]List举例:
a6WI170^1 [font="Times] import java.util.*;
Z`KC%!8K [font="Times]public class ListExample {
Nz],IG. [font="Times] public static void main(String[] args) {
RWgNo#< [font="Times] List list = new ArrayList();
JQ6zVS2SSS [font="Times] list.add("one");
)`A3M) [font="Times] list.add("second");
Vc2A [font="Times] list.add("3rd");
n3D;"a3 [font="Times] list.add(new Integer(4));
d[V;&U [font="Times] list.add(new Float( 5.0F ));
o8-^cP1 [font="Times] list.add("second");
IbP#_Vt [font="Times] list.add(new Integer(4));
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th [font="Times] System.out.println(list);
8$;=Uf,x [font="Times] }}
]2\VweV 79xx2 EodQ*{l [font="Times]Map举例
pXtX jb [font="Times]import java.util.Map;
j{9D{ [font="Times]import java.util.HashMap;
nAjO6g6E [font="Times]import java.util.Iterator;
[`rba' [font="Times]import java.io.FileReader;
glF; eT [font="Times]
Y<Fz)dQo [font="Times]public class MapExample {
{O`w,dMOI [font="Times] public static void main(String[] args) throws java.io.FileNotFoundException {
'4|-9M3f [font="Times] Map word_count_map = new HashMap();
}9W4"e 2) [font="Times] FileReader reader = new FileReader(args[0]);
?l^1 *Q, [font="Times] Iterator words = new WordStreamIterator(reader);
zN"J}r: [font="Times]
P)MDPI+~ [font="Times] while ( words.hasNext() ) {
(KF=On;=Y [font="Times] String word = (String) words.next();
twlk-2yT! [font="Times] String word_lowercase = word.toLowerCase();
; o0&`b? [font="Times] Integer frequency = (Integer)word_count_map.get(word_lowercase);
#EsNeBu [font="Times]if ( frequency == null ) {
I$0)Px%z [font="Times] frequency = new Integer(1);
,Qnd3[2[ [font="Times] } else {
oze& [font="Times] int value = frequency.intValue();
k+8q{5>A< [font="Times] frequency = new Integer(value + 1);}
@ vrV*! [font="Times] word_count_map.put(word_lowercase, frequency);
JaL%qco [font="Times] }
NwG= <U* [font="Times] System.out.println(word_count_map);
,H19`;Q [font="Times] }}
G6FEp` 3YFU*f, XAe%m^ [font="Times]Queue举例:
kZerKP [font="Times]import java.io.IOException;
iMP]W_ [font="Times]import java.io.PrintStream;
^WNrGF [font="Times]import java.util.LinkedList;
[ zEUH:9D [font="Times]import java.util.Queue;
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qAqkS [font="Times]
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[font="Times]public class QueueTester {
52,m:EhL [font="Times] public Queue q; //发现了一个奇怪的语法,这个尖括号是泛型声明
0 SNIYkGE [font="Times] public QueueTester() {q = new LinkedList();}
I{*<