Java-类库-Guava-Multimap

在日常的开发工作中，我们有的时候需要构造像Map

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import org.junit.Test;

public class MultimapTest {

    Map<String, List<StudentScore>> StudentScoreMap = new HashMap<String, List<StudentScore>>();

    @Test
    public void testStudentScore(){

        for(int i=10;i<20;i++){
            StudentScore studentScore=new StudentScore();
            studentScore.CourseId=1001+i;
            studentScore.score=100-i;
            addStudentScore("peida",studentScore);
        }

        System.out.println("StudentScoreMap:"+StudentScoreMap.size());
        System.out.println("StudentScoreMap:"+StudentScoreMap.containsKey("peida"));

        System.out.println("StudentScoreMap:"+StudentScoreMap.containsKey("jerry"));
        System.out.println("StudentScoreMap:"+StudentScoreMap.size());
        System.out.println("StudentScoreMap:"+StudentScoreMap.get("peida").size());

        List<StudentScore> StudentScoreList=StudentScoreMap.get("peida");
        if(StudentScoreList!=null&&StudentScoreList.size()>0){
            for(StudentScore stuScore:StudentScoreList){
                System.out.println("stuScore one:"+stuScore.CourseId+" score:"+stuScore.score);
            }
        }
    }

    public void addStudentScore(final String stuName,final StudentScore studentScore) {
        List<StudentScore> stuScore = StudentScoreMap.get(stuName);
        if (stuScore == null) {
            stuScore = new ArrayList<StudentScore>();
            StudentScoreMap.put(stuName, stuScore);
        }
        stuScore.add(studentScore);
    }
}

class StudentScore{
    int CourseId;
    int score;
}

　说明：想 Map

　@Test
    public void teststuScoreMultimap(){
        Multimap<String,StudentScore> scoreMultimap = ArrayListMultimap.create(); 
        for(int i=10;i<20;i++){
            StudentScore studentScore=new StudentScore();
            studentScore.CourseId=1001+i;
            studentScore.score=100-i;
            scoreMultimap.put("peida",studentScore);
        }
        System.out.println("scoreMultimap:"+scoreMultimap.size());
        System.out.println("scoreMultimap:"+scoreMultimap.keys());
    }

　调用Multimap.get(key)会返回这个键对应的值的集合的视图（view），没有对应集合就返回空集合。对于ListMultimap来说，这个方法会返回一个List，对于SetMultimap来说，这个方法就返回一个Set。修改数据是通过修改底层Multimap来实现的。例如：

　@Test
    public void teststuScoreMultimap(){
        Multimap<String,StudentScore> scoreMultimap = ArrayListMultimap.create(); 
        for(int i=10;i<20;i++){
            StudentScore studentScore=new StudentScore();
            studentScore.CourseId=1001+i;
            studentScore.score=100-i;
            scoreMultimap.put("peida",studentScore);
        }
        System.out.println("scoreMultimap:"+scoreMultimap.size());
        System.out.println("scoreMultimap:"+scoreMultimap.keys());

        Collection<StudentScore> studentScore = scoreMultimap.get("peida");
        studentScore.clear();
        StudentScore studentScoreNew=new StudentScore();
        studentScoreNew.CourseId=1034;
        studentScoreNew.score=67;
        studentScore.add(studentScoreNew);

        System.out.println("scoreMultimap:"+scoreMultimap.size());
        System.out.println("scoreMultimap:"+scoreMultimap.keys());
    }

Multimap也支持一系列强大的视图功能：
　　1.asMap把自身Multimap

@Test
    public void teststuScoreMultimap(){
        Multimap<String,StudentScore> scoreMultimap = ArrayListMultimap.create(); 
        for(int i=10;i<20;i++){
            StudentScore studentScore=new StudentScore();
            studentScore.CourseId=1001+i;
            studentScore.score=100-i;
            scoreMultimap.put("peida",studentScore);
        }
        System.out.println("scoreMultimap:"+scoreMultimap.size());
        System.out.println("scoreMultimap:"+scoreMultimap.keys());

        Collection<StudentScore> studentScore = scoreMultimap.get("peida");
        StudentScore studentScore1=new StudentScore();
        studentScore1.CourseId=1034;
        studentScore1.score=67;
        studentScore.add(studentScore1);

        StudentScore studentScore2=new StudentScore();
        studentScore2.CourseId=1045;
        studentScore2.score=56;
        scoreMultimap.put("jerry",studentScore2);

        System.out.println("scoreMultimap:"+scoreMultimap.size());
        System.out.println("scoreMultimap:"+scoreMultimap.keys());


        for(StudentScore stuScore : scoreMultimap.values()) {
            System.out.println("stuScore one:"+stuScore.CourseId+" score:"+stuScore.score);
        }

        scoreMultimap.remove("jerry",studentScore2); 
        System.out.println("scoreMultimap:"+scoreMultimap.size());
        System.out.println("scoreMultimap:"+scoreMultimap.get("jerry"));

        scoreMultimap.put("harry",studentScore2);
        scoreMultimap.removeAll("harry");
        System.out.println("scoreMultimap:"+scoreMultimap.size());
        System.out.println("scoreMultimap:"+scoreMultimap.get("harry"));
    }

　Multimap的实现

　　Multimap提供了丰富的实现，所以你可以用它来替代程序里的Map