Java 8 sum list of objects

the following types of grouping and summation requirements are common in mysql

select a, b, c, sum[d] from t group by a

by sql standards ，b，c column does not use the aggregate function in oracle the middle one will report an error, while the middle one will report an error mysql a loose group by mode, b，c the values are random, and now i have a set java what should an object do if it wants to do something similar

List users; User u1 = new User["tom", "bb", "cc", 100] User u2 = new User["tom", "bb", "cc", 50] User u3 = new User["jerry", "dd", "ee", 30] User u2 = new User["jerry", "dd", "ee",40]

finally, i want to use the stream stream to achieve the following effect of grouping sum

User["tom", "bb", "cc", 150] User["jerry", "dd", "ee", 70]

how to use stream ### problem description

the background of the problem and the methods i have tried

the relevant code

// paste the code text below （ do not use pictures instead of code ）

what results do you expect ？ what is the actual error message that you see ？

first time answer, hope can help you

User class ：

class User { String name; String phone; String address; Long scope; public User[String name, String phone, String address] { this.name = name; this.phone = phone; this.address = address; } public User[String name, String phone, String address, Long scope] { this.name = name; this.phone = phone; this.address = address; this.scope = scope; } @Override public String toString[] { return "User{" + "name='" + name + '\'' + ", phone='" + phone + '\'' + ", address='" + address + '\'' + ", scope=" + scope + '}'; } @Override public boolean equals[Object o] { if [this == o] return true; if [o == null || getClass[] != o.getClass[]] return false; User user = [User] o; return Objects.equals[name, user.name] && Objects.equals[phone, user.phone] && Objects.equals[address, user.address] && Objects.equals[scope, user.scope]; } @Override public int hashCode[] { return Objects.hash[name, phone, address]; } }

rewrite equals and hashCode it's for grouping.
tostring is rewritten to print User the specific attribute value of

the main body function

public class MyTest { public static void main[String[] args] { ArrayList users = new ArrayList[]; users.add[new User["tom", "bb", "cc", 100l]]; users.add[new User["tom", "bb", "cc", 50l]]; users.add[new User["jerry", "dd", "ee", 30l]]; users.add[new User["jerry", "dd", "ee",40l]]; users.stream[] .collect[Collectors .groupingBy[ user -> new User[user.name, user.phone, user.address], Collectors.summarizingLong[user -> user.scope] ] ] .forEach[[k,v] -> { k.scope = v.getSum[]; System.out.println[k]; }]; } }

the results

User{name='jerry', phone='dd', address='ee', scope=70} User{name='tom', phone='bb', address='cc', scope=150}