集合框架学习之Guava Collection

Posted 2020-10-15

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