Java 8 - convert list of objects to map (from List<User> to Map<Long, User> - long to object / counter)

List<User> users = Arrays.asList(new User(1, "Ann"), new User(2, "Tom"));

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Map<Long, User> usersMap = users.stream().collect(

        Collectors.toMap(User::getUserId, user -> user));

​

// {1=User{userId=1, name='Ann'}, 2=User{userId=2, name='Tom'}}

System.out.println(usersMap);

List<User> users = Arrays.asList(new User(1, "Ann"), new User(2, "Tom"));

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Map<Long, User> usersMap2 = users.stream().collect(

        Collectors.toMap(User::getUserId, Function.identity()));

​

// {1=User{userId=1, name='Ann'}, 2=User{userId=2, name='Tom'}}

System.out.println(usersMap2);

import java.util.Arrays;

import java.util.List;

import java.util.Map;

import java.util.function.Function;

import java.util.stream.Collectors;

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public class Example {

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    public static void main(String[] args) {

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        List<User> users = Arrays.asList(new User(1, "Ann"), new User(2, "Tom"));

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        // example 1 with lambda

        Map<Long, User> usersMap = users.stream().collect(

                Collectors.toMap(User::getUserId, user -> user));

​

        // {1=User{userId=1, name='Ann'}, 2=User{userId=2, name='Tom'}}

        System.out.println(usersMap);

​

        // example 2 with Function.identity()

        Map<Long, User> usersMap2 = users.stream().collect(

                Collectors.toMap(User::getUserId, Function.identity()));

​

        // {1=User{userId=1, name='Ann'}, 2=User{userId=2, name='Tom'}}

        System.out.println(usersMap2);

    }

​

    private static class User {

        private final long userId;

        private final String name;

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        public User(long userId, String name) {

            this.userId = userId;

            this.name = name;

        }

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        public long getUserId() {

            return userId;

        }

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        public String getName() {

            return name;

        }

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        @Override

        public String toString() {

            return "User{" +

                    "userId=" + userId +

                    ", name='" + name + '\'' +

                    '}';

        }

    }

}