guava入门学习3（集合工具）

3.1 Iterables

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3.1.1concat() 拼接集合

List<String> l1 = Lists.newArrayList("1");

List<String> l2 = Lists.newArrayList("2");

Iterable<String> concat = Iterables.concat(l1, l2);

concat.forEach(System.out::println);

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3.1.2元素在指定集合中出现的次数

int frequency = Iterables.frequency(l1, "1”);

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3.1.3Partition() 按指定元素个数拆分集合

List<String> l1 = Lists.newArrayList("1","2","3","4","5");

Iterable<List<String>> partition = Iterables.partition(l1, 2);

partition.forEach(System.out::println);

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3.1.4比较两个集合，当两个集合中的元素值都相等且顺序一样时，返回true

List<String> l1 = Lists.newArrayList("1","2","3","4","51");

List<String> l2 = Lists.newArrayList("1","2","3","4",new String("5")+"1");

boolean b = Iterables.elementsEqual(l1, l2);

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3.1.5截取集合的前指定位数作为视图遍历

List<String> l1 = Lists.newArrayList("1","2","3","4",”5”,”6”,”7");

Iterable<String> limit = Iterables.limit(l1, 6);

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3.2Sets

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3.2.1powerSet() 返回所有的子集，包含空集和自身全集

Set<String> set1 = Sets.newHashSet("1","2");

Set<Set<String>> sets = Sets.powerSet(set1);

sets.forEach(System.out::println);

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3.2.2Sets.cartesianProduct(Set ...) 返回集合的笛卡尔积 集合个数不限

Set<String> set1 = Sets.newHashSet("1","2");

Set<String> set2 = Sets.newHashSet("a","b");

Set<List<String>> lists = Sets.cartesianProduct(Lists.newArrayList(set1, set2));

lists.forEach(System.out::println);

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3.3Maps

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3.3.1difference.entriesInCommon 返回两个map中健值对都相等

Map<String,String> m1 = Maps.newHashMapWithExpectedSize(16);

Map<String,String> m2 = Maps.newHashMapWithExpectedSize(16);

m1.put("a","a1");

m2.put("a","a1");

m1.put("b","b1");

m2.put("b","b2");

m1.put("c","c1");

MapDifference<String, String> difference = Maps.difference(m1, m2);

Map<String, String> stringStringMap = difference.entriesInCommon();

System.out.println(stringStringMap);

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3.3.2difference.entriesDiffering()  返回不相等的键值对

Map<String, MapDifference.ValueDifference<String>> stringValueDifferenceMap = difference.entriesDiffering();

System.out.println(stringValueDifferenceMap);

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3.3.3只存在于左边的键值对

Map<String, String> onlyOnLeftMap = difference.entriesOnlyOnLeft();

System.out.println(onlyOnLeftMap);

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3.3.4只存在于右边的键值对

Map<String, String> onlyOnRightMap = difference.entriesOnlyOnRight();

System.out.println(onlyOnRightMap);

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3.4Tables

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3.4.1转置二维表

Table<String,String,String> table = HashBasedTable.create();

table.put("r1","c1","r1c1");

table.put("r1","c2","r1c2");

table.put("r2","c1","r2c1");

System.out.println(table);

Table<String, String, String> transpose = Tables.transpose(table);

System.out.println(transpose);

—输出：

{r1={c1=r1c1, c2=r1c2}, r2={c1=r2c1}}

{c1={r1=r1c1, r2=r2c1}, c2={r1=r1c2}}