Guava collections -- Sets

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Guava全文介绍地址:Google Guava
这次主要介绍是的是com.google.common.collect.Sets.主要的作用是就与Java Set相关的静态的实用方法。在Guava中与之类似的还有Lists,Maps以及Queues这些类。
下面就介绍一个Sets的主要用法:

1、笛卡尔集

    @Test    public void testCartesianProduct(){        Set<String> s1 = Sets.newHashSet("Foo","Bar");        Set<String> s2 = Sets.newHashSet("Jim","Bob");        Set<List<String>> cartesian  = Sets.cartesianProduct(s1, s2);        List<String> list = Lists.newArrayList();        list.add("Foo");        list.add("Jim");        assertThat(cartesian.contains(list),is(true));        list.clear();        list.add("Foo");        list.add("Bob");        assertThat(cartesian.contains(list),is(true));        list.clear();        list.add("Bar");        list.add("Jim");        assertThat(cartesian.contains(list),is(true));        list.clear();        list.add("Bar");        list.add("Bob");        assertThat(cartesian.contains(list),is(true));    }

2、返回2个set前一个包含后一个不包含的所有的元素

    @Test    public void testSetDifference() {        Set<String> s1 = Sets.newHashSet("1","2","3");        Set<String> s2 = Sets.newHashSet("3","2","4");        Sets.SetView<String> sv = Sets.difference(s1,s2);        assertThat(sv.size()==1 && sv.contains("1"),is(true));        sv = Sets.difference(s2,s1);        assertThat(sv.size()==1 && sv.contains("4"),is(true));    }

3、返回2个set，共同元素以外的所有元素

    @Test    public void testSymmetricDifference(){        Set<String> s1 = Sets.newHashSet("1","2","3");        Set<String> s2 = Sets.newHashSet("3","2","4");        Sets.SetView<String> sv = Sets.symmetricDifference(s1,s2);        assertThat(sv.size()==2 && sv.contains("1") && sv.contains("4"),is(true));    }

4、返回2个set的交集

    @Test    public void testIntersection(){        Set<String> s1 = Sets.newHashSet("1","2","3");        Set<String> s2 = Sets.newHashSet("3","2","4");        Sets.SetView<String> sv = Sets.intersection(s1,s2);        assertThat(sv.size()==2 && sv.contains("2") && sv.contains("3"),is(true));    }

5、返回2个set的并集

    @Test    public void testUnion(){        Set<String> s1 = Sets.newHashSet("1","2","3");        Set<String> s2 = Sets.newHashSet("3","2","4");        Sets.SetView<String> sv = Sets.union(s1,s2);        assertThat(sv.size()==4 &&                sv.contains("2") &&                sv.contains("3") &&                sv.contains("4") &&                sv.contains("1"),is(true));    }

呵呵，全是数学中的集合操作。当然Sets也可以和Predicate结合起来进行函数式编程。
更多功能等待你的发现。

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