guava 例子

import com.google.common.base.*;
import com.google.common.base.Optional;
import com.google.common.collect.*;

import java.text.SimpleDateFormat;
import java.util.*;


public class GuavaTester {
    public String ss = "123";

    public static void main (String args[]) {

        // nullOptional();
        //GuavaTester t =new GuavaTester();
        // t.objects();
        // range();
        //preconditions();
        //ordering();
        //throwables();
        //multiset();
        //bimap();
        //table();
        //===========
        //list();
        //filter();
        //transform();
        //compose();
        // testGuava6();
        //testGuava7();
        //multiset();
        //multimap();
        //biMap();
        //===========
        //LoadingCache
        //Joiner
        //Splitter
        //CharMatcher
        //CaseFormat
    }

    /**
     * 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)
     */
    public static void biMap () {
        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);
    }

    public static void multimap () {
        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);
        }
    }

    /**
     * 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
     */
    public static 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));
        }
    }

    public static void multiset () {
        Multiset<Integer> multiset = HashMultiset.create();
        multiset.add(new Integer(1));
        multiset.add(new Integer(1));
        multiset.stream().forEach(x -> System.out.print(x + " "));
        System.out.println();
        Set<Integer> integers = multiset.elementSet();
        System.out.println("=" + integers.size() + "=");
    }

    public static void transform () {
        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);
        }
    }

    public static void filter () {
        //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
        }
    }

    public static void list () {
        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
    }

    public static void table () {
        Table<String, String, String> employeeTable = HashBasedTable.create();
        employeeTable.put("IBM", "101", "Mahesh");
        Map<String, String> ibmEmployees = employeeTable.row("IBM");
    }

    public static void bimap () {
        BiMap<Integer, String> empIDNameMap = HashBiMap.create();
        empIDNameMap.put(new Integer(101), "Mahesh");
        empIDNameMap.put(new Integer(102), "Sohan");
        empIDNameMap.put(new Integer(103), "Ramesh");
        System.out.println(empIDNameMap.inverse().get("Mahesh"));
        empIDNameMap.putIfAbsent(104, "hansc");
        empIDNameMap.computeIfAbsent(104, k -> k + "x");
        empIDNameMap.forEach((k, v) -> System.out.println("key = " + k + ",value=" + v));
    }

    public static void throwables () {
        // Throwables.propagateIfPossible();
    }

    public static void ordering () {

        List<Integer> numbers = new ArrayList<Integer>();
        numbers.add(new Integer(5));
        numbers.add(new Integer(2));
        numbers.add(new Integer(15));
        numbers.add(new Integer(51));

        Ordering ordering = Ordering.natural();
        System.out.println("Input List: ");
        System.out.println(numbers);

        Collections.sort(numbers, ordering);
        System.out.println("Sorted List: ");
        System.out.println(numbers);
        System.out.println("======================");
        System.out.println("List is sorted: " + ordering.isOrdered(numbers));
        System.out.println("Minimum: " + ordering.min(numbers));
        System.out.println("Maximum: " + ordering.max(numbers));

        Collections.sort(numbers, ordering.reverse());
        System.out.println("Reverse: " + numbers);

        numbers.add(null);
        numbers.add(1);
        numbers.add(1000);
        System.out.println("Null added to Sorted List: ");
        System.out.println(numbers);

        Collections.sort(numbers, ordering.nullsFirst().reverse());
        System.out.println("Null first Sorted List: ");
        System.out.println(numbers);
        System.out.println("======================");
    }

    public static void preconditions () {
        Preconditions.checkArgument(0 < 1, "sorry ,you are wrong");
        String s = "";
        Preconditions.checkNotNull(s, "%s ... %s", "哈哈", "呵呵");
    }

    public static void range () {

        Range<Integer> range = Range.closed(1, 3);

        if (range.contains(2)) {
            System.out.print("true");
        }

        Range<Short> all = Range.all();

        System.out.println(all.atLeast(100));

        DiscreteDomain discreteDomain = DiscreteDomain.integers();
        long distance = discreteDomain.distance(3, 6);
        System.out.println(distance);
        ContiguousSet<Integer> contiguousSet = ContiguousSet.create(range, discreteDomain);
        for (Integer i : contiguousSet) {
            System.out.println(i + " ");
        }
    }

    private static void nullOptional () {
        Integer value = 1;
        // of 非空 检查， 否则抛出异常
        Optional<Integer> a = Optional.of(value);
        Optional<Integer> b = Optional.of(new Integer(1));

        // asSet 返回单值得集合
        System.out.println("asSet 返回单值得集合 = " + a.asSet());

        // Optional equals 方法
        System.out.println("Optional equals 方法" + a.equals(b));

        System.out.println(sum(a, b));

        Integer nullEle = 1;

        Optional<Integer> c = Optional.of(nullEle);

        nullEle = c.or(123);
        System.out.println("absent = " + c.absent().isPresent());
        //System.out.println("fromNullable = " + c.fromNullable());
        System.out.println(c.orNull());

        c = Optional.fromNullable(null);
        c.get();
    }

    public static Integer sum (Optional<Integer> a, Optional<Integer> b) {
        return a.get() + b.get();
    }

    /**
     * 集合操作：交集、差集、并集
     */
    public void testGuava6 () {
        Set<Integer> set1 = Sets.newHashSet(1, 2, 3, 4);
        Set<Integer> set2 = Sets.newHashSet(3, 4, 5, 6);
        //交集
        Sets.SetView<Integer> inter = Sets.intersection(set1, set2);
        //差集
        Sets.SetView<Integer> diff = Sets.difference(set1, set2);
        //并集
        Sets.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，
    }

    /**
     * 组合式函数编程
     */
    public void compose () {
        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
               */
        }
    }

    public void objects () {
        String s = "first";
        String s2 = "test";
        String res = MoreObjects.firstNonNull(s, s2);
        System.out.println(res);

        MoreObjects.ToStringHelper toStringHelper = MoreObjects.toStringHelper(this);
        toStringHelper.add("hansc", "123");
        System.out.print(toStringHelper.toString());
        // java 8 StringJoiner 替代 MoreObjects.toStringHelper
        String string = new StringJoiner(", ", this.getClass().getSimpleName() + "[", "]")
                .add("userId=" + 1)
                .add("timestamp=" + 2)
                .toString();
        System.out.print(string);
    }
}

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