Java中List集合按需求转换为Map集合

class Faculty{
    //专业id
    private Integer id;
    //班级名称
    private String name;
    public void setId(Integer id){
        this.id = id;
    }
    public Integer getId(){
        return id;
    }
    public void setName(String name){
        this.name= name;
    }
    public String getName(){
        return name;
    }
}


public class Main{
    public static void main(String[] args){
        //声明一个List集合
        List list = new ArrayList();  
        list.add(new Faculty("1001", "计科01"));  
        list.add(new Faculty("1002", "计科02"));  
        list.add(new Faculty("1003", "计科03"));
        System.out.println(list);
        //将list转换map
        Map map = list.stream().collect(Collectors.toMap(Faculty::getId, Faculty::getName));                                                                                 
        System.out.println(map);
    }
}

class Faculty{
    //专业id
    private Integer id;
    //班级名称
    private String name;
    public void setId(Integer id){
        this.id = id;
    }
    public Integer getId(){
        return id;
    }
    public void setName(String name){
        this.name= name;
    }
    public String getName(){
        return name;
    }
}


public class Main{
    public static void main(String[] args){
        //声明一个List集合
        List list = new ArrayList();  
        list.add(new Faculty("1001", "A"));  
        list.add(new Faculty("1002", "B"));  
        list.add(new Faculty("1002", "C"));
        list.add(new Faculty("1003", "D"));
        list.add(new Faculty("1003", "E"));
        list.add(new Faculty("1003", "F"));
        System.out.println(list);


        //将list转换map  key为专业id， value是 相同专业id的所包含的不同班级名称
        Map> map = list.stream().collect(Collectors.toMap(Faculty::getId,
	    		p ->  {
	    		 	List getNameList = new ArrayList<>();
	    		 		getNameList.add(p.getName());
	    		 		return getNameList;
	    		 	},
    		     	(List value1, List value2) -> {
    		     		value1.addAll(value2);
    		     		return value1;
    		     	}
	    		 ));
       
         System.out.println(map);

    }
}

class Faculty{
    //专业id
    private Integer id;
    //班级名称
    private String name;
    public void setId(Integer id){
        this.id = id;
    }
    public Integer getId(){
        return id;
    }
    public void setName(String name){
        this.name= name;
    }
    public String getName(){
        return name;
    }
}


public class Main{
    public static void main(String[] args){
        //声明一个List集合
        List list = new ArrayList();  
        list.add(new Faculty("1001", "A"));  
        list.add(new Faculty("1002", "B"));  
        list.add(new Faculty("1002", "C"));
        list.add(new Faculty("1003", "D"));
        list.add(new Faculty("1003", "E"));
        list.add(new Faculty("1003", "F"));
        System.out.println(list);

		//将list转换map  key为专业id， value是 相同专业id的所包含的不同班级名称
		Map> map = new HashMap<>();
		for(Faculty faculty : list){
			List nameList = map.getOrDefaulty(faculty.getId(),new ArrayList<>());
			nameList.add(faculty.getName());
			map.put(faculty.getId,nameList);
		}
        System.out.println(map);

    }
}