走近Guava(三): 集合
集合：
FluentIterable类：
- 使用FluentIterable.filter过滤, 即利用Predicate实现：
Iterable<Person> adults = FluentIterable.from(ps).filter(
new Predicate<Person>() {
@Override
public boolean apply(Person p) {
return p.getAge() >= 18; // 年龄>18
}
});
- 使用FluentIterable.transform()转换，即利用Function实现：
FluentIterable.from(ps).transform(new Function<Person, String>() {
@Override
public String apply(Person p) {
return Joiner.on('#').join(p.getName(), p.getAge());
}
});
Lists类：
- 使用Lists.newArrayList创建列表：
ps = Lists.newArrayList(
new Person("person1", 22),
new Person("person2", 23),
new Person("person3", 17)
);
- 使用Lists.partition()方法分割列表：
//[a, b, c, d, e] --> [[a, b], [c, d, e]] - List<List<Person>> subList = Lists.partition(ps, 2);
Sets类：
- Sets.difference()求S1-S2
Set<String> s1 = Sets.newHashSet("1", "2", "3");
Set<String> s2 = Sets.newHashSet("2", "3", "4");
Sets.difference(s1, s2); //[1]
- Sets.intersection()求S1,S2交集
Set<String> s1 = Sets.newHashSet("1", "2", "3");
Set<String> s2 = Sets.newHashSet("3", "2", "4");
Sets.SetView<String> sv = Sets.intersection(s1, s2); // [2, 3]
- Sets.union()求合集
Set<String> s1 = Sets.newHashSet("1", "2", "3");
Set<String> s2 = Sets.newHashSet("3", "2", "4");
Sets.SetView<String> sv = Sets.union(s1, s2); // [3, 2, 1 ,4]
Maps类：
- Maps.uniqueIndex()将列表转换为map
//iterator各个元素作为Map.values, key为Function.apply返回值
Maps.uniqueIndex(ps.iterator(), new Function<Person, String>() {
@Override
public String apply(Person p) {
return p.getName();
}
});
- Maps.asMap()，<K, V>和Maps.uniqueIndex()相反
Maps.asMap(ps, new Function<Person, String>() {
@Override
public String apply(Person p) {
return p.getName();
}
});
- Maps Transform API:
Maps.transformEntries(map, new Maps.EntryTransformer<String, Boolean, String>() {
@Override
public String transformEntry(String key, Boolean value) {
return value ? "yes" : "no";
}
}); 将Map<String, Boolean> --> Map<String, String>, 其他的还有Maps.transformValues转换值
Multimaps:
- 一个key对应多个value。
ArrayListMultiMap:
ArrayListMultimap<String, String> multiMap = ArrayListMultimap.create();
multiMap.put("Foo", "1");
multiMap.put("Foo", "2");
multiMap.put("Foo", "3");
System.out.println(multiMap); // {Foo=[1,2,3]} 当出现重复值时，依然会被添加，因为ArrayListMultiMap的value时一个ArrayList:
ArrayListMultimap<String, String> multiMap = ArrayListMultimap.create();
multiMap.put("Bar", "1");
multiMap.put("Bar", "2");
multiMap.put("Bar", "3");
multiMap.put("Bar", "3");
multiMap.put("Bar", "3");
System.out.println(multiMap); //{Bar=[1, 2, 3, 3, 3]}，相同的value会重复，value内部是一个List
HashMultiMap:
HashMultimap<String, String> multiMap = HashMultimap.create();
multiMap.put("Bar", "1");
multiMap.put("Bar", "2");
multiMap.put("Bar", "3");
multiMap.put("Bar", "3");
multiMap.put("Bar", "3");
System.out.println(multiMap); //{Bar=[3, 2, 1]}, 相同的value不会重复，value内部是一个Set
其他一些MultiMap:
LinkedHashMultimap //顺序的HashMultimap, 形如LinkedHashMap TreeMultimap //可排序的MultiMap, 形如TreeMap //一些不可变的map ImmutableListMultimap ImmutableMultimap ImmutableSetMultimap
BiMap:
- 其限制value是唯一的，且通过value可以找到key
BiMap<String,String> biMap = HashBiMap.create();
biMap.put("1","Tom");
biMap.put("2","Tom"); //抛出异常
- BiMap.forcePut()强制放入value相等的entry:
BiMap<String, String> biMap = HashBiMap.create();
biMap.put("1", "Tom");
biMap.forcePut("2", "Tom");
System.out.println(biMap); //{2=Tom}
- BiMap.inverse()反转key-value
BiMap<String, String> biMap = HashBiMap.create();
biMap.put("1", "Tom");
biMap.put("2", "Harry");
BiMap<String, String> inverseMap = biMap.inverse();
System.out.println(biMap); //{2=Harry, 1=Tom}
System.out.println(inverseMap); //{Harry=2, Tom=1
Table:
- 它具有2个key[行, 列]，对应一个值。
HashBasedTable:
- 通用操作
HashBasedTable<Integer, Integer, String> table = HashBasedTable.create();
table.put(1, 1, "Rook");
table.put(1, 2, "Knight");
table.put(1, 3, "Bishop");
System.out.println(table.contains(1, 1)); //true
System.out.println(table.containsColumn(2)); //true
System.out.println(table.containsRow(1)); //true
System.out.println(table.containsValue("Rook")); //true
System.out.println(table.remove(1, 3)); //Bishop
System.out.println(table.get(3, 4)); //null
- Table views，表行列视图
Map<Integer,String> columnMap = table.column(1); Map<Integer,String> rowMap = table.row(2);
- 其他table
ArrayTable //二维数组实现 ImmutableTable //不可变table，创建后不能改变 TreeBasedTable //对行列排序的table
Range:
- 代表一种范围的类。
Range<Integer> numberRange = Range.closed(1, 10); //包括首尾 System.out.println(numberRange.contains(10)); //true System.out.println(numberRange.contains(1)); //true Range<Integer> numberRange1 = Range.open(1,10); //除去首尾 System.out.println(numberRange1.contains(10)); //false System.out.println(numberRange1.contains(1)); //false
- Range和Function组合成Predicate的过滤条件
Range<Integer> ageRange = Range.closed(35, 50);
//Person到age转换的function
Function<Person, Integer> ageFunction = new Function<Person, Integer>() {
@Override
public Integer apply(Person person) {
return person.getAge();
}
};
//这样得到年龄再[35, 50]之间的人
Predicate<Person> predicate = Predicates.compose(ageRange,ageFunction);
- 创建不可变的集合
MultiMap<Integer,String> map = new ImmutableListMultimap.Builder<Integer,String>() .put(1,"Foo").putAll(2,"Foo","Bar","Baz") .putAll(4,"Huey","Duey","Luey") .put(3,"Single").build();
Ordering:
- Ordering提供了一些简单强大的排序功能。
/**
* 城市人口比较器
*/
public class CityByPopluation implements Comparator<City> {
@Override
public int compare(City city1, City city2) {
return Ints.compare(city1.getPopulation(), city2.getPopulation());
}
}
- 反序
Ordering.from(cityByPopluation).reverse();
- 处理Null
Ordering.from(comparator).nullsFirst();//null值最小放在前面
- 二次排序
/**
* 雨量比较器
*/
public class CityByRainfall implements Comparator<City> {
@Override
public int compare(City city1, City city2) {
return Doubles.compare(city1.getAverageRainfall(),
city2.getAverageRainfall());
}
}
Ordering<City> secondaryOrdering = Ordering.from(cityByPopulation).compound(cityByRainfall);//组合比较器 Collections.sort(cities,secondaryOrdering); //排序
- 获取最大最小
Ordering<City> ordering = Ordering.from(cityByPopluation); List<City> topFive = ordering.greatestOf(cityList,5); //前5个 List<City> bottomThree = ordering.leastOf(cityList,3); //最后3个看来Guava在集合方面还是很给力的。
不吝指正。