因为是有序的

import java.util.LinkedHashMap;
import java.util.Map;


public class TestGeneral {

public static void main(String[] args) {

//store orignal User and Country
Map<String , String> hmOriginal = new LinkedHashMap<String , String>();
hmOriginal.put("John", "Canada");
hmOriginal.put("Bob", "USA");
hmOriginal.put("Tom", "USA");
hmOriginal.put("Alice", "Canada");
hmOriginal.put("Alan", "Canada");
hmOriginal.put("Peter", "UK");


//store Updated data
Map<String , String> hmUpdated = new LinkedHashMap<String , String>();

for (Map.Entry<String, String> entry : hmOriginal.entrySet())
{
String sName = entry.getKey();
String sCountry = entry.getValue();

if( !hmUpdated.containsValue(sCountry))
{
hmUpdated.put(sName, sCountry);
}

}

System.out.println("Original data is :"+hmOriginal );
System.out.println("Updated data is :"+hmUpdated );

}

}