集合框架学习之Guava Collection

开源工具包：

Guava : Google Collection

Apache：Commons Collecton

1.1 Google Collections

Guava:google的工程师利用传说中的“20%时间”开发的集合库，它是对jdk提供的扩展，提供了很多使用的类来简化代码

jar包：https://code.google.com/p/guava-libraries/

源码下载：

下载git工具：（易于本地增加分支和分布式的特性）

msysgit:http://code.google.com/p/msysgit/downloads/list

命令：git clone 网络路径本地文件夹（不存在或空文件夹）

/**
* Guava集合框架
* @author qjc
*
* 2016-3-12
*/
public class Demo {
/**
* 只读设置
*/
@Test
public void testGuava1(){
List<String> list = new ArrayList<>();
list.add("a");
list.add("b");
list.add("c");
//对原有的list进行包装，相当于原有List的一个试图，快照，不够安全
List<String> readList = Collections.unmodifiableList(list);
//java.lang.UnsupportedOperationException
//        readList.add("d");
list.add("d"); //改变原有List 试图也一起改变
//对比查看初始化List guava对只读设置 安全可靠，并且相对简单
List<String> immutableList = ImmutableList.of("a","b","c");
immutableList.add("d");//java.lang.UnsupportedOperationException
}
/**
* 函数式编程:过滤器
*/
@Test
public void testGuava2(){
//创建List 静态初始化
List<String> list = Lists.newArrayList("moon","son","dad","refer");
//找出回文 palindronme backwoeds mirror words
Collection<String> palindromeList = Collections2.filter(list, new Predicate<String>() {
@Override
public boolean apply(String input) {
//业务逻辑
return new StringBuilder(input).reverse().toString().equals(input);
}
});
for(String temp : palindromeList){
System.out.println(temp);
//输出结果：dad refer
}
}
/**
*  函数式编程:转换
*/
@Test
public void testGuava3(){
Set<Long> timeSet = Sets.newHashSet();
//类型转换
timeSet.add(19990701L);
timeSet.add(20080808L);
timeSet.add(20161212L);
Collection<String> timeStrCol = Collections2.transform(timeSet, new Function<Long,String>(){
@Override
public String apply(Long input) {
return new SimpleDateFormat("yyyy-MM-dd").format(input);
}
});
for(String temp : timeStrCol){
System.out.println(temp);
}
}
/**
* 组合式函数编程
*     确保容器中的字符串长度不超过5，超过进行截取，然后全部大写
*/
@Test
public void testGuava4(){
List<String> list = Lists.newArrayList("abcde","good","happiness");
//确保容器中的字符串长度不超过5
Function<String, String> f1 = new Function<String, String>() {
@Override
public String apply(String input) {
return input.length()>5?input.substring(0, 5):input;
}
};
//转成大写
Function<String, String> f2 = new Function<String, String>() {
@Override
public String apply(String input) {
return input.toUpperCase();
}
};
//String = f2(f1(String))
Function<String, String> f = Functions.compose(f1, f2);
Collection<String> resultCol = Collections2.transform(list, f);
for(String str:resultCol){
System.out.println(str);
/*
* 输出结果：
ABCDE
GOOD
HAPPI
*/
}
}
/**
* 加入约束：非空、长度验证
*/
@Test
public void testGuava5(){
Set<String> sets = Sets.newHashSet();
//创建约束
Constraint<String> constraint = new Constraint<String>() {

@Override
public String checkElement(String element) {
//非空验证
Preconditions.checkNotNull(element);
//长度验证 5~20位字符串
Preconditions.checkArgument(element.length()>=5 && element.length()<20);
return element;
}
};
Set<String> cs = Constraints.constrainedSet(sets, constraint);
//        cs.add(null);    //java.lang.NullPointerException
//        cs.add("abcd"); //java.lang.IllegalArgumentException
cs.add("abcde");//ok
}
/**
* 集合操作：交集、差集、并集
*/
@Test
public void testGuava6(){
Set<Integer> set1 =Sets.newHashSet(1,2,3,4);
Set<Integer> set2 =Sets.newHashSet(3,4,5,6);
//交集
SetView<Integer> inter = Sets.intersection(set1, set2);
//差集
SetView<Integer> diff = Sets.difference(set1, set2);
//并集
SetView<Integer> union = Sets.union(set1, set2);
//遍历输出:交集 ：3,4 差集：1，2，5,6 并集：1,2,3,4,5,6，
}
/**
* 统计单词出现的次数
* 1、HashMap 分拣存储+面向对象思维   --->判断
* 2、Multiset:无序可重复  .count()  增强可读性+操作简单
*/
@Test
public void testGuava7(){
String str = "this is a cat and that is mice where is the food";
//分割字符串
String[] arr = str.split(" ");
//存储到Multiset中
Multiset<String> set = HashMultiset.create();
for(String ss:arr){
set.add(ss);
}
//获取所有的单词set
Set<String> letters = set.elementSet();
for(String temp:letters){
System.out.println(temp+":"+set.count(temp));
}
}
/**
* 分析查看每个教师教授的没门课程
* Multimap   key也可以重复
*/
@Test
public void testGuava8(){
Map<String, String> map = new HashMap<String, String>();
//加入测试数据
map.put("改革开放", "邓爷爷");
map.put("三个代表", "江主席");
map.put("科学发展观", "胡主席");
map.put("和谐社会", "胡主席");
map.put("八荣八耻", "胡主席");
//Multimap
Multimap<String, String> teacher = ArrayListMultimap.create();
//迭代器
Iterator<Map.Entry<String, String>> it = map.entrySet().iterator();
while(it.hasNext()){
Map.Entry<String, String> entry = it.next();
String key = entry.getKey(); //课程
String value = entry.getValue(); //教师
//教师--->课程
teacher.put(value, key);
}
//查看Multimap
Set<String> keySet = teacher.keySet();
for(String key:keySet){
Collection<String> col = teacher.get(key);
System.out.println(key+":"+col);
}
}
/**
* HashMap 键唯一,值可以重复
* BiMap:双向Map(bidirectional Map) 键与值不能重复(unique -valued map)
*/
@Test
public void testGuava9(){
BiMap<String, String> biMap = HashBiMap.create();
biMap.put("sina", "@sina.com");
biMap.put("qq", "@qq.com");
//通过邮箱找用户
String user = biMap.inverse().get("@sina.com");
System.out.println(user);
System.out.println(biMap.inverse().inverse()==biMap);
}
/**
* 双键的Map -->Table --->rowKey+columnKye+value
*/
@Test
public void testGuava10(){
Table<String, String, Integer> table = HashBasedTable.create();
//测试数据
table.put("龙傲天", "java", 50);
table.put("龙傲天", "oracle", 60);
table.put("福尔康", "java", 70);
table.put("福尔康", "oracle", 100);
//所有的行数据
Set<Cell<String, String, Integer>> cells = table.cellSet();
for(Cell<String, String, Integer> temp : cells){
System.out.println(temp.getRowKey()+":"+temp.getColumnKey()+":"+temp.getValue());
}
/*
龙傲天:java:50
龙傲天:oracle:60
福尔康:java:70
福尔康:oracle:100*/
System.out.println("=======学生查看成绩========");
System.out.print("学生\t");
//所有的课程
Set<String> cours = table.columnKeySet();
for(String t : cours){
System.out.print(t+"\t");
}
System.out.println();
//所有的学生
Set<String> stus = table.rowKeySet();
for(String stu:stus){
System.out.print(stu+"\t");
Map<String,Integer> scores  = table.row(stu);
for(String c:cours){
System.out.print(scores.get(c)+"\t");
}
System.out.println();
}
/*
学生       java     oracle
龙傲天    50     60
福尔康    70     100*/
}
}

小结:

1.只读设置:immutableList

2.函数式编程:解耦

1) predicate

2)Function

工具:

Collections2.filter()过滤器

Collections2.transfer()转换

Functions.compose()组合式函数编程

3.加入约束条件:非空 长度验证

Constraint

Preconditions

4.集合的操作:交集差集并集

Sets.intersection()

Sets.difference()

Sets.union()

5.Multiset Multimap BiMap

6.Table