list.stream().collect(Collectors.groupingBy(ClassEntity::getGrade));

list.stream()
.collect(Collectors.collectingAndThen(Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(o -> o.getProfessionId() + ";" + o.getGrade()))), ArrayList::new));

List<String> classNameList = new ArrayList(new HashSet(list));

class User { 
    private int id;
    private String name;
    private Integer record; 
    public User() {
    }
 
    public User(int id,String name, Integer record) {
    }
 
    public int getId() { 
        return id;
    }
 
    public void setId(int id) { 
        this.id = id;
    }
 
    public String getName() { 
        return name;
    }
 
    public void setName(String name) { 
        this.name = name;
    }
 
    public Integer getRecord() { 
        return record;
    }
 
    public void setRecord(Integer record) { 
        this.record = record;
    }
 
}

public class Main {
    public static void main(String[] args) {
    List<User> users = new ArrayList<>();
    User user1 = new User();
        user1.setId(1);
        user1.setName("小明");
        user1.setRecord(50);
        users.add(user1);
    User user2 = new User();
        user2.setId(1);
        user2.setName("小明");
        user2.setRecord(60);
        users.add(user2);
    User user3 = new User();
        user3.setId(2);
        user3.setName("小華");
        user3.setRecord(70);
        users.add(user3);
    User user4 = new User();
        user4.setId(2);
        user4.setName("小華");
        user4.setRecord(80);
        users.add(user4);
    User user5 = new User();
        user5.setId(3);
        user5.setName("小芳");
        user5.setRecord(100);
        users.add(user5);
 
        Map<String, Integer> conver = new HashMap();
        users.stream().forEach(x -> {
            String cKey = x.getId()+"_"+x.getName();
            if (!conver.containsKey(cKey)) {
                conver.put(cKey, x.getRecord());
            } else {
                Integer temp = conver.get(cKey);
                conver.put(cKey, (null == temp ? 0 : temp) + (null == x.getRecord() ? 0 : x.getRecord()));
            }
        });
        System.out.println(conver.size());
        for(Map.Entry<String, Integer> entry:conver.entrySet()){
            System.out.println("key:"+entry.getKey()+","+"value:"+entry.getValue());
        }
    }
}