Guava(石榴)使用研究-Google开源Collection类库
1)Guava?简介
Guava 中文是石榴的意思，该项目是 Google 的一个开源项目，包含许多 Google 核心的 Java 常用库。
目前主要包含：
在线API doc：http://www.osctools.net/apidocs/apidoc?api=guava
2)代码实现
package test;
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import java.text.DecimalFormat;
import java.util.Arrays;
import java.util.Collection;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.TimeUnit;
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import com.google.common.base.Function;
import com.google.common.base.Predicate;
import com.google.common.collect.Collections2;
import com.google.common.collect.HashMultimap;
import com.google.common.collect.HashMultiset;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Lists;
import com.google.common.collect.MapMaker;
import com.google.common.collect.Ordering;
import com.google.common.collect.ImmutableSet.Builder;
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/**
?* @author gaozzsoft
?*
?*/
public class MyGuavaTest {
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/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
List list = Lists.newArrayList();
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//1 Immutable Collections: 真正的不可修改的集合
Set<String> set = new HashSet<String>(Arrays.asList(new String[]{"RED", "GREEN"}));?
Set<String> unmodifiableSet = Collections.unmodifiableSet(set);?
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ImmutableSet<String> immutableSet = ImmutableSet.of("RED", "GREEN");?
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ImmutableSet<String> immutableSet2 = ImmutableSet.copyOf(set);?
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Builder<String> ?builder = ImmutableSet.builder();?
ImmutableSet<String> immutableSet3 = builder.add("RED").addAll(set).build();?
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// Multiset: 把重复的元素放入集合
List<String> wordList =Arrays.asList(new String[]{"RED", "GREEN"});
Map<String, Integer> map = new HashMap<String, Integer>();?
for(String word : wordList){?
? ?Integer count = map.get(word);?
? ?map.put(word, (count == null) ? 1 : count + 1);?
}?
//count word “RED”
Integer count = map.get("RED");?
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// Quit good method
HashMultiset<String> multiSet = HashMultiset.create();?
multiSet.addAll(wordList);?
//count word “RED”
Integer count2 = multiSet.count("RED");?
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//2 Multimap: 在 Map 的 value 里面放多个元素
//Key is candidate name, its value is his voters?
HashMap<String, HashSet<String>> hMap = new HashMap<String, HashSet<String>>();?
List<Ticket> tickets = Lists.newArrayList();
Ticket ticket1 = new Ticket("xijinping","gaozz");
Ticket ticket2 = new Ticket("xijinping","saiwg");
tickets.add(ticket1);
tickets.add(ticket2);
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for(Ticket ticket: tickets){?
? ?HashSet<String> set2 = hMap.get(ticket.getCandidate());?
? ?if(set2 == null){?
? ?set2 = new HashSet<String>();?
? ? ? ?hMap.put(ticket.getCandidate(), set2);?
? ?}?
? ?set2.add(ticket.getVoter());?
}
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HashMultimap<String, String> map2 = HashMultimap.create();?
for(Ticket ticket: tickets){?
? ?map2.put(ticket.getCandidate(), ticket.getVoter());?
}?
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//3 BiMap: 双向 Map
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// for(Map.Entry<User, Address> entry : map.entreSet()){?
// ? ?if(entry.getValue().equals(anAddess)){?
// ? ? ? ?return entry.getKey();?
// ? ?}?
// }?
// ? ? return null;?
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// return biMap.inverse().get(anAddess);?
// biMap == biMap.inverse().inverse();
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//4 MapMaker: 超级强大的 Map 构造工具
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//ConcurrentHashMap with concurrency level 8?
ConcurrentMap<String, Object> map1 = new MapMaker()?
? ?.concurrencyLevel(8)?
? ? .makeMap();?
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//ConcurrentMap with soft reference key and weak reference value?
ConcurrentMap<String, Object> map3 = new MapMaker()?
? ?.softKeys()?
? ?.weakValues()?
? ?.makeMap();?
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//Automatically removed entries from map after 30 seconds since they are created?
ConcurrentMap<String, Object> map4 = new MapMaker()
? ?.expireAfterWrite(30, TimeUnit.SECONDS)?
? ?.makeMap();
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//Map size grows close to the 100, the map will evict?
//entries that are less likely to be used again?
ConcurrentMap<String, Object> map5 = new MapMaker()
? ?.maximumSize(100)?
? ?.makeMap();?
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//Create an Object to the map, when get() is missing in map?
ConcurrentMap<String, Object> map6 = new MapMaker()?
? ?.makeComputingMap(?
? ? ?new Function<String, Object>() {?
? ? ? ?public Object apply(String key) {?
// ? ? ? ? ?return createObject(key);?
? ? ? ?return null;
? ?}});?
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//Put all features together! ?强大之处
ConcurrentMap<String, Object> mapAll = new MapMaker()?
? ?.concurrencyLevel(8)?
? ?.softKeys()?
? ?.weakValues()?
? ?.expireAfterWrite(30, TimeUnit.SECONDS)?
? ?.maximumSize(100)?
? ?.makeComputingMap(?
? ? ?new Function<String, Object>() {?
? ? ? ?public Object apply(String key) {?
// ? ? ? ? ?return createObject(key);?
? ? ? ? ?return null;
? ? }});?
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//5 元素排序
//假设有个待排序的 List<Foo>，而 Foo 里面有两个排序关键字 int a, int b 和 int c
// Collections.sort(list, new Comparator<Foo>(){ ? ?
// ? ?@Override ? ?
// ? ?public int compare(Foo f1, Foo f2) { ? ?
// ? ? ? ?int resultA = f1.a – f2.a;?
// ? ? ? ?int resultB = f1.b – f2.b;?
// ? ? ? ?return ?resultA == 0 ? (resultB == 0 ? f1.c – f2.c : resultB) : resultA;?
//}});
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// Collections.sort(list, new Comparator<Foo>(){ ? ?
// ? ?@Override?
// ? ?return ComparisonChain.start() ?
// ? ? ? ? .compare(f1.a, f2.a) ?
// ? ? ? ? .compare(f1.b, f2.b)?
// ? ? ? ? .compare(f1.c, f2.c).result();?
//}});
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// Foo 里面每个排序关键字都已经有了各自的 Comparator，那么利用 ComparisonChain 可以?
// Collections.sort(list, new Comparator<Foo>(){ ? ?
// ? ?@Override?
// ? ?return ComparisonChain.start() ?
// ? ? ? ? .compare(f1.a, f2.a, comparatorA) ?
// ? ? ? ? .compare(f1.b, f2.b, comparatorB)?
// ? ? ? ? .compare(f1.c, f2.c, comparatorC).result();?
// ?}});
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//Ordring 类还提供了一个组合 Comparator 对象的方法
// 而且 Ordring 本身实现了 Comparator 接口所以它能直接作为 Comparator 使用
// Ordering<Foo> ordering = Ordering.compound(
// ? ? Arrays.asList(comparatorA, comparatorB, comparatorC));?
// Collections.sort(list, ordering);
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//6 过滤器&&转换器
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//过滤器
Collection<Integer> ?filterCollection =?
? ? ? ?Collections2.filter(list, new Predicate<Integer>(){?
// ? ?@Override?
? ?public boolean apply(Integer input) {?
? ? ? ?return input >= 10;?
}});?
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//转换器
Set<Integer> ?setTmp = null;
Collection<String> ?formatCollection =?
? ? ?Collections2.transform(setTmp, new Function<Integer, String>(){?
// ? ?@Override?
? ?public String apply(Integer input) {?
? ? ? ?return new DecimalFormat("#,###").format(input);?
}} );?
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}
}
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