TreeMultimap（guava） 使用：

原理解析：

(37条消息) Guava TreeMultiSet实现原理分析_云中漫步87的博客-CSDN博客_guava 树形结构

于HashMap中键值是不排序的，所以如果你需要排序的Multimap的话就需要使用guava中的TreeMultimap。

类：com.google.common.collect.TreeMultimap

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TreeMultimap<Integer,Integer> map = TreeMultimap.create();
         
map.put(2, 4);
map.put(1, 2);
map.put(1, 3);
map.put(2, 6);
map.put(2, 4);
map.put(3, 6);
map.put(11, 2);
map.put(21, 6);
map.put(6, 7);

修改值

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map.remove(3, 6);
map.put(12, 3);

遍历

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Iterator iter = map.entries().iterator();
while(iter.hasNext())
{
        Map.Entry<Integer, Integer> entry = (Map.Entry<Integer, Integer>)iter.next();
        System.out.println(String.format("%d:%d", entry.getKey(),entry.getValue()));
}

结果：
1:2
1:3
2:4
2:6
6:7
11:2
12:3
21:6

用时（Mills）9
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Set<Integer> keys = map.keySet();
for(int key:keys)
{
     String result = String.format("%d:", key);
     Set<Integer> values = map.get(key);
     for(int value:values)
     {
     	result = result+" "+value;
     }
     System.out.println(result);
}

结果：
1: 2 3
2: 4 6
6: 7
11: 2
12: 3
21: 6

用时（Mills）：8
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public class Investor implements Comparator<Investor>{
    private String name;
    private String id;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Investor{" +
                "id=" + getId() +
                ", name='" + name
                '}';
    }
    @Override
    public int hashCode(){
        final int prime=31;
        int result = 1;
        result = prime * result + ((this.getId() == null) ? 0 : this.getId().hashCode());
        return result;
    }

    @Override
    public int compare(Investor first, Investor second) {
        if (first == second) {
            return 0;
        } else if (first == null) {
            return -1;
        } else if (second == null) {
            return 1;
        } else if (first.getId() != second.getId()) {
            return (int)(first.getId() - second.getId());
        } else {
            return first.getId().compareTo(second.getId());
        }
    }

    @Override
    public boolean equals(Object obj){
        if(this==obj)
            return true;
        if(obj==null)
            return false;
        if(getClass()!=obj.getClass())
            return false;
        Investor other=(Investor)obj;
        if(this.getId()==null){
            if(other.getId()!=null){
                return false;
            }else if(!this.getId().equals(other.getId())){
                return false;
            }
        }
        return true;
    }
}

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**通过Ordering.from指定排序方式**
TreeMultimap investor = TreeMultimap.create(Ordering.natural(),
                                                              Ordering.from(investorComparator));