1. ???? ???? ?? ? ??

?? ??? ???? ??????? ?? ??? ???? ???? ????? ??? ???? ???? ??? ??? ? ????. Java Streams? ???? ??? ??? ?? ?? ? ????.

?? ??

import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

class User {
    private int id;
    private String name;

    // Constructors, getters, setters
}

public class EntityCacheExample {
    public static void main(String[] args) {
        List<User> users = List.of(
            new User(1, "Alice"),
            new User(2, "Bob"),
            new User(3, "Charlie")
        );

        Map<Integer, User> userCache = users.stream()
            .collect(Collectors.toMap(User::getId, user -> user));

        System.out.println(userCache);
    }
}

? ????? Collectors.toMap()? ???? User ?? ??? ?? ??? ID?? ?? User ?? ??? Map?? ?????. ??? ?? ??? ???? ??? ????? ?????.

?? ??

{1=User{id=1, name='Alice'}, 2=User{id=2, name='Bob'}, 3=User{id=3, name='Charlie'}}

2. ??? ?? ???

?? ??? ???? ?? ???? ???? ? ? ??? ? ????. ?? ?? ???? ???? ???? ?? ???? ???? ? ????.

?? ??

import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

class User {
    private String department;
    private String role;
    private String name;

    // Constructors, getters, setters
}

public class NestedMapExample {
    public static void main(String[] args) {
        List<User> users = List.of(
            new User("HR", "Manager", "Alice"),
            new User("IT", "Developer", "Bob"),
            new User("IT", "Manager", "Charlie")
        );

        Map<String, Map<String, List<User>>> nestedMap = users.stream()
            .collect(Collectors.groupingBy(User::getDepartment,
                Collectors.groupingBy(User::getRole)));

        System.out.println(nestedMap);
    }
}

? ??? Collectors.groupingBy()? ???? ??? Map? ???? ??? ?????. ?? Map? ???? ???? ?????, ?? Map? ???? ???? ??????.

?? ??

{HR={Manager=[User{name='Alice'}]}, IT={Developer=[User{name='Bob'}], Manager=[User{name='Charlie'}]}}

3. ? ?? ?? ?? ? ??

??? ?? ?? ?? ?? ?? ??? ???? ?? ?? ????. ??
?? >
? ???? ???? ? ? ????.

?? ??

import java.util.List;
import java.util.Map;
import java.util.AbstractMap.SimpleEntry;
import java.util.stream.Collectors;

class User {
    private int id;
    private String name;
    private int age;

    // Constructors, getters, setters
}

public class MapWithTwoValuesExample {
    public static void main(String[] args) {
        List<User> users = List.of(
            new User(1, "Alice", 30),
            new User(2, "Bob", 25),
            new User(3, "Charlie", 35)
        );

        Map<Integer, Map.Entry<String, Integer>> userMap = users.stream()
            .collect(Collectors.toMap(User::getId, user -> 
                new SimpleEntry<>(user.getName(), user.getAge())));

        System.out.println(userMap);
    }
}

????? SimpleEntry? ???? ? ??? ID? ??? ? ?? ?(?? ? ??)? ?? ??? ?????.

?? ??

{1=Alice=30, 2=Bob=25, 3=Charlie=35}

4. ??? ?? ? ??

???? ??? ?? ???? ?? ??? ? ??? ?? ??? ???? ???? ??? ???? ? ??? ??? ??? ???? ? ????.

?? ??

import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

class User {
    private String department;
    private String name;

    // Constructors, getters, setters
}

public class GroupingByMappingExample {
    public static void main(String[] args) {
        List<User> users = List.of(
            new User("HR", "Alice"),
            new User("IT", "Bob"),
            new User("HR", "Charlie")
        );

        Map<String, List<String>> groupedMap = users.stream()
            .collect(Collectors.groupingBy(User::getDepartment,
                Collectors.mapping(User::getName, Collectors.toList())));

        System.out.println(groupedMap);
    }
}

? ???? ???? ???? ???? ?? User ??? ?? ??? ???? ? ??? ?? ??? ??? ?? ????.

?? ??

{HR=[Alice, Charlie], IT=[Bob]}

5. ???, ?? ? ??

???, ??, ??? ???? ?? ????? ? ??? ???? ?? ? ???? ????? ??? ? ????.

?? ??

import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

class Transaction {
    private String type;
    private int amount;

    // Constructors, getters, setters
}

public class GroupingByMappingReducingExample {
    public static void main(String[] args) {
        List<Transaction> transactions = List.of(
            new Transaction("Deposit", 100),
            new Transaction("Deposit", 200),
            new Transaction("Withdrawal", 50),
            new Transaction("Withdrawal", 30)
        );

        Map<String, Integer> transactionSums = transactions.stream()
            .collect(Collectors.groupingBy(Transaction::getType,
                Collectors.reducing(0, Transaction::getAmount, Integer::sum)));

        System.out.println(transactionSums);
    }
}

? ????? ??? ???? ????? ??? ??? ?? ???? ??? ????. ??? ? ?? ??? ?? ??? ???? ?????.

?? ??

import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

class User {
    private int id;
    private String name;

    // Constructors, getters, setters
}

public class EntityCacheExample {
    public static void main(String[] args) {
        List<User> users = List.of(
            new User(1, "Alice"),
            new User(2, "Bob"),
            new User(3, "Charlie")
        );

        Map<Integer, User> userCache = users.stream()
            .collect(Collectors.toMap(User::getId, user -> user));

        System.out.println(userCache);
    }
}

6. ??

??? ?? Java Stream ??? ?? ???? ???? ?? ???? ? ????. ??? ??? ??? ??? ??? ?? ??? ?? ??? ? ????. ??? ??? ?? ??? ??? ?? ??? ??? ?????!

?? ? ?? ???? ?????. ??? ? 5?? ?? Java ??? ??

? ??? ??? ? ?? Java ??? ??? ?? ?????. ??? ??? PHP ??? ????? ?? ?? ??? ?????!