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Исправили!","topic_id":100791},{"creator":{"public_name":"Nika","id":679616,"is_tutor":false},"id":192562,"body":"Кстати, и здесь, и в предыдущем задании у вас стоят , или ; после последнего объекта в листе, который мы как бы передаем в наш метод. но в таком виде компилятор в IDE будет ругаться","topic_id":100791}],"communitable":{"parent_entity_name":null,"parent_entity_url":null,"entity_name":"Списки в определении типов","entity_url":null,"active":true}},{"id":94207,"title":"Вопрос: 3 из 3. Вы ответили верно на 2\nЧто на дает завязка в коде на интерфейс, а не на конкретный класс?\n\nОпечатка: Что на**м** дает...","plain_title":"Вопрос: 3 из 3. Вы ответили верно на 2 Что на дает завязка в коде на интерфейс, а не на конкретный класс? Опечатка: Что нам дает... ","creator":{"public_name":"Selsh","id":720417,"is_tutor":false},"comments":[{"creator":{"public_name":"Maksim Litvinov","id":198906,"is_tutor":true},"id":184519,"body":"Спасибо, поправил","topic_id":94207}],"communitable":{"parent_entity_name":null,"parent_entity_url":null,"entity_name":"Списки в определении типов","entity_url":null,"active":true}},{"id":94334,"title":"Почему в случае с LinkedList в теории в комментах стоит \"Упс\", если указано, что код будет работать?","plain_title":"Почему в случае с LinkedList в теории в комментах стоит \"Упс\", если указано, что код будет работать? ","creator":{"public_name":"Максим Сироткин","id":663711,"is_tutor":false},"comments":[{"creator":{"public_name":"Maksim Litvinov","id":198906,"is_tutor":true},"id":184694,"body":"Да, поправил, спасибо","topic_id":94334}],"communitable":{"parent_entity_name":null,"parent_entity_url":null,"entity_name":"Списки в определении типов","entity_url":null,"active":true}},{"id":104527,"title":"\"Этот код не скомпилируется, потому что тип переменной friends будет List<User>, а не ArrayList<User> как ожидается\". Тут в теории криво сформулировали - видимо имели в виду конкретный тип \"List.of\". Просто же List<User> как раз интерфейс и он заработает.","plain_title":"\"Этот код не скомпилируется, потому что тип переменной friends будет List, а не ArrayList как ожидается\". Тут в теории криво сформулировали - видимо имели в виду конкретный тип \"List.of\". Просто же List как раз интерфейс и он заработает. ","creator":{"public_name":"Виктор","id":719594,"is_tutor":false},"comments":[{"creator":{"public_name":"Виктор","id":719594,"is_tutor":false},"id":197088,"body":"Ещё в тестах первое предложение почему-то вопросительное, хотя там утверждение.","topic_id":104527},{"creator":{"public_name":"Maksim Litvinov","id":198906,"is_tutor":true},"id":197101,"body":"Приветствую, Виктор!\n\nОпечатку в квизе поправил, спасибо!\n\n> Просто же List<User> как раз интерфейс и он заработает.\n\nА попробуйте запустить этот код, заработает ли?\n\n```\n| Error:\n| incompatible types: java.util.List<User> cannot be converted to java.util.ArrayList<User>\n| user.setFriends(friends);\n| ^-----^\n```\n\n","topic_id":104527},{"creator":{"public_name":"Виктор","id":719594,"is_tutor":false},"id":197120,"body":"**Maksim Litvinov**, хм, любопытно. Просто по идее тут конфликт конкретных реализаций List.of и ArrayList. Странно что Джава в ошибке пишет про List (конвертируемый интерфейс), а не List.of (реализация в коде). Код, да, не заработает, но причина немного другая вроде. Впрочем, если такую формулировку выдает и сам Джава, то ладно..","topic_id":104527}],"communitable":{"parent_entity_name":null,"parent_entity_url":null,"entity_name":"Списки в определении типов","entity_url":null,"active":true}}],"lesson":{"exercise":{"id":2798,"slug":"java_lists_lists_in_types_exercise","name":null,"state":"active","kind":"exercise","language":"java","locale":"ru","has_web_view":false,"has_test_view":false,"reviewable":true,"readme":"В этом упражнении мы лишний раз потренируемся обрабатывать списки, а заодно применим подход, рассмотренный в уроке.\n\n## src/main/java/io/hexlet/App.java\n\nВ классе `App` реализуйте публичный статический метод `countBooks()`, который посчитает общее количество книг автора. Метод принимает три параметра\n\n- Список книг\n- Имя автора, строка\n- Жанр, строка\n\nМетод должен вернуть общее количество книг в библиотеке, написанных нашим автором в определенном жанре\n\n```java\nvar books = List.of(\n new Book(\"Death on the Nile\", \"Agatha Christie\", \"Detective\"),\n new Book(\"Murder on the Orient Express\", \"Agatha Christie\", \"Detective\"),\n new Book(\"The Raven\", \"Edgar Allan Poe\", \"Poem\")\n);\n\nApp.countBooks(books, \"Agatha Christie\", \"Detective\"); // 2\n```\n\nРеализуйте метод так, чтобы он мог принимать в качестве списка книг любую реализацию интерфейса `List`\n","prepared_readme":"В этом упражнении мы лишний раз потренируемся обрабатывать списки, а заодно применим подход, рассмотренный в уроке.\n\n## src/main/java/io/hexlet/App.java\n\nВ классе `App` реализуйте публичный статический метод `countBooks()`, который посчитает общее количество книг автора. Метод принимает три параметра\n\n- Список книг\n- Имя автора, строка\n- Жанр, строка\n\nМетод должен вернуть общее количество книг в библиотеке, написанных нашим автором в определенном жанре\n\n```java\nvar books = List.of(\n new Book(\"Death on the Nile\", \"Agatha Christie\", \"Detective\"),\n new Book(\"Murder on the Orient Express\", \"Agatha Christie\", \"Detective\"),\n new Book(\"The Raven\", \"Edgar Allan Poe\", \"Poem\")\n);\n\nApp.countBooks(books, \"Agatha Christie\", \"Detective\"); // 2\n```\n\nРеализуйте метод так, чтобы он мог принимать в качестве списка книг любую реализацию интерфейса `List`\n","has_solution":true,"entity_name":"Списки в определении типов"},"units":[{"id":10392,"name":"theory","url":"/courses/java-lists/lessons/lists-in-types/theory_unit"},{"id":10436,"name":"quiz","url":"/courses/java-lists/lessons/lists-in-types/quiz_unit"},{"id":10435,"name":"exercise","url":"/courses/java-lists/lessons/lists-in-types/exercise_unit"}],"links":[{"id":425040,"name":"Интерфейс List","url":"https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/util/List.html\n"}],"ordered_units":[{"id":10392,"name":"theory","url":"/courses/java-lists/lessons/lists-in-types/theory_unit"},{"id":10436,"name":"quiz","url":"/courses/java-lists/lessons/lists-in-types/quiz_unit"},{"id":10435,"name":"exercise","url":"/courses/java-lists/lessons/lists-in-types/exercise_unit"}],"id":4438,"slug":"lists-in-types","state":"approved","name":"Списки в определении типов","course_order":270,"goal":"Изучить правильный способ описания типов списков в определении полей и методов классов","self_study":null,"theory_video_provider":null,"theory_video_uid":null,"theory":"На примере коллекций, мы первый раз столкнулись с типами данных, которые завязаны на интерфейс и имеют несколько его реализаций. Определение свойств и методов с такой структурой отличается от того, как мы до этого работали с примитивными типами.\n\nРассмотрим пример, когда мы работаем с числами или строками, то определяем свойства и методы соответственно:\n\n```java\nclass Point {\n private int x;\n private int y;\n\n public int getX() {\n return x;\n }\n public void setX(int x) {\n this.x = x;\n }\n public int getY() {\n return y;\n }\n public void setY(int y) {\n this.y = y;\n }\n}\n```\n\nЗдесь мы указываем ровно тот тип, про который мы думаем. Применим такой же подход к спискам. Создадим класс пользователя, у которого есть возможность добавлять друзей:\n\n```java\nimport java.util.ArrayList;\n\nclass User {\n private ArrayList<User> friends;\n\n public ArrayList<User> getFriends() {\n return friends;\n }\n\n public void setFriends(ArrayList<User> friends) {\n this.friends = friends;\n }\n}\n```\n\nПока все выглядит отлично, но посмотрите на возможный пример использования.\n\n```java\nimport java.util.List;\n\nvar user = new User();\nvar friends = List.of(new User(), new User());\nuser.setFriends(friends); // Упс\n```\n\nЭтот код не скомпилируется, потому что тип переменной `friends` будет `List<User>`, а не `ArrayList<User>` как ожидается. Правильным выходом из этой ситуации будет завязка не на конкретную реализацию `ArrayList`, а на интерфейс `List`.\n\n```java\nimport java.util.List;\n\nclass User {\n private List<User> friends;\n\n public List<User> getFriends() {\n return friends;\n }\n\n public void setFriends(List<User> friends) {\n this.friends = friends;\n }\n}\n```\n\nПочему именно так? Фактически в этом и есть смысл интерфейсов. Реализация может поменяться, но код от этого меняться не должен, если интерфейс не меняется. Код выше работает с любой конкретной реализацией:\n\n```java\nimport java.util.ArrayList;\n\nvar user = new User();\nvar friends = new ArrayList<User>();\nfriends.add(new User());\nfriends.add(new User());\nuser.setFriends(friends);\n```\n\nСегодня мы решили использовать `ArrayList`, а завтра захотели поменять его на `LinkedList`, потому что так будет эффективнее. Код по-прежнему будет работать:\n\n```java\nimport java.util.LinkedList;\n\nvar user = new User();\nvar friends = new LinkedList<User>();\nfriends.add(new User());\nfriends.add(new User());\nuser.setFriends(friends);\n```\n"},"lessonMember":null,"courseMember":null,"course":{"start_lesson":{"exercise":null,"units":[{"id":10388,"name":"theory","url":"/courses/java-lists/lessons/intro/theory_unit"}],"links":[],"ordered_units":[{"id":10388,"name":"theory","url":"/courses/java-lists/lessons/intro/theory_unit"}],"id":4434,"slug":"intro","state":"approved","name":"Введение","course_order":100,"goal":"Познакомиться с курсом","self_study":null,"theory_video_provider":null,"theory_video_uid":null,"theory":"Списки – это одна из наиболее важных структур данных, которые позволяют организовать и управлять коллекциями объектов в Java-приложениях. В отличие от массивов, коллекции умеют работать с динамическими коллекциями, в которых количество элементов со временем меняется.\n\nВаше понимание списков в Java будет играть ключевую роль в разработке эффективных и масштабируемых приложений. Независимо от того, являетесь ли вы начинающим программистом, ищущим основы работы с Java, или опытным разработчиком, стремящимся углубить свои знания и навыки, этот курс предоставит вам все необходимое для понимания и использования списков в Java.\n\nВ течение этого курса мы рассмотрим различные типы списков, такие как `ArrayList`, `LinkedList` и другие, и изучим, как эффективно добавлять, удалять, изменять и получать элементы из списков. Мы также рассмотрим методы сортировки, поиск элементов, и обсудим различные сценарии применения списков в реальных проектах.\n"},"id":381,"slug":"java-lists","challenges_count":5,"name":"Java: Списки","allow_indexing":true,"state":"approved","course_state":"finished","pricing_type":"paid","description":"В этом курсе изучаются списки, один из главных строительных блоков программ на Java. Вы познакомитесь с различными видами списков, которые часто используются в Java. Вы узнаете про различные методы, которые помогают работать с коллекциями элементов. В итоге вы научитесь создавать коллекции, наполнять их данными, добавлять и удалять элементы. На курсе вы отработаете на практике эффективные способы обхода коллекций, сортировки и выполнения различных агрегирующих операций. Знания из этого курса помогут вам уверенно работать со списками.","kind":"additional","updated_at":"2026-01-20T11:51:23.563Z","language":"java","duration_cache":33840,"skills":["Эффективно работать с коллекциями элементов","Обходить коллекции различными способами","Сортировать списки элементов в нужном порядке"],"keywords":[],"lessons_count":8,"cover":"/vite/assets/course-DLoqF1jj.png"},"recommendedLandings":[{"stack":{"id":3,"slug":"java","title":"Java-разработчик","audience":"for_beginners","start_type":"weekly","pricing_model":"purchase","priority":"high","kind":"profession","state":"published","stack_state":"finished","order":30,"duration_in_months":10},"id":3,"slug":"java","title":"Java-разработчик","subtitle":"Изучите Java и фреймворк Spring Boot и REST API","subtitle_for_lists":"Изучите Java и фреймворк Spring Boot и REST API","locale":"ru","current":true,"duration_in_months_text":"10 месяцев","stack_slug":"java","price_text":"от 6 792 ₽","duration_text":"10 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0.05);--mantine-color-red-filled: var(--mantine-color-red-5);--mantine-color-red-filled-hover: var(--mantine-color-red-6);--mantine-color-red-light: rgba(236, 120, 120, 0.15);--mantine-color-red-light-hover: rgba(236, 120, 120, 0.2);--mantine-color-red-light-color: var(--mantine-color-red-0);--mantine-color-red-outline: var(--mantine-color-red-1);--mantine-color-red-outline-hover: rgba(254, 212, 212, 0.05);--mantine-color-pink-filled: var(--mantine-color-pink-5);--mantine-color-pink-filled-hover: var(--mantine-color-pink-6);--mantine-color-pink-light: rgba(250, 162, 193, 0.15);--mantine-color-pink-light-hover: rgba(250, 162, 193, 0.2);--mantine-color-pink-light-color: var(--mantine-color-pink-0);--mantine-color-pink-outline: var(--mantine-color-pink-1);--mantine-color-pink-outline-hover: rgba(255, 222, 235, 0.05);--mantine-color-grape-filled: var(--mantine-color-grape-5);--mantine-color-grape-filled-hover: var(--mantine-color-grape-6);--mantine-color-grape-light: rgba(229, 153, 247, 0.15);--mantine-color-grape-light-hover: rgba(229, 153, 247, 0.2);--mantine-color-grape-light-color: var(--mantine-color-grape-0);--mantine-color-grape-outline: var(--mantine-color-grape-1);--mantine-color-grape-outline-hover: rgba(243, 217, 250, 0.05);--mantine-color-violet-filled: var(--mantine-color-violet-5);--mantine-color-violet-filled-hover: var(--mantine-color-violet-6);--mantine-color-violet-light: rgba(209, 111, 255, 0.15);--mantine-color-violet-light-hover: rgba(209, 111, 255, 0.2);--mantine-color-violet-light-color: var(--mantine-color-violet-0);--mantine-color-violet-outline: var(--mantine-color-violet-1);--mantine-color-violet-outline-hover: rgba(241, 207, 255, 0.05);--mantine-color-indigo-filled: var(--mantine-color-indigo-5);--mantine-color-indigo-filled-hover: var(--mantine-color-indigo-6);--mantine-color-indigo-light: rgba(123, 121, 235, 0.15);--mantine-color-indigo-light-hover: rgba(123, 121, 235, 0.2);--mantine-color-indigo-light-color: var(--mantine-color-indigo-0);--mantine-color-indigo-outline: var(--mantine-color-indigo-1);--mantine-color-indigo-outline-hover: rgba(214, 213, 254, 0.05);--mantine-color-blue-filled: var(--mantine-color-blue-5);--mantine-color-blue-filled-hover: var(--mantine-color-blue-6);--mantine-color-blue-light: rgba(116, 192, 252, 0.15);--mantine-color-blue-light-hover: rgba(116, 192, 252, 0.2);--mantine-color-blue-light-color: var(--mantine-color-blue-0);--mantine-color-blue-outline: var(--mantine-color-blue-1);--mantine-color-blue-outline-hover: rgba(208, 235, 255, 0.05);--mantine-color-cyan-filled: var(--mantine-color-cyan-5);--mantine-color-cyan-filled-hover: var(--mantine-color-cyan-6);--mantine-color-cyan-light: rgba(100, 218, 255, 0.15);--mantine-color-cyan-light-hover: rgba(100, 218, 255, 0.2);--mantine-color-cyan-light-color: var(--mantine-color-cyan-0);--mantine-color-cyan-outline: var(--mantine-color-cyan-1);--mantine-color-cyan-outline-hover: rgba(202, 245, 255, 0.05);--mantine-color-teal-filled: var(--mantine-color-teal-5);--mantine-color-teal-filled-hover: var(--mantine-color-teal-6);--mantine-color-teal-light: rgba(99, 230, 190, 0.15);--mantine-color-teal-light-hover: rgba(99, 230, 190, 0.2);--mantine-color-teal-light-color: var(--mantine-color-teal-0);--mantine-color-teal-outline: var(--mantine-color-teal-1);--mantine-color-teal-outline-hover: rgba(195, 250, 232, 0.05);--mantine-color-green-filled: var(--mantine-color-green-5);--mantine-color-green-filled-hover: var(--mantine-color-green-6);--mantine-color-green-light: rgba(134, 223, 148, 0.15);--mantine-color-green-light-hover: rgba(134, 223, 148, 0.2);--mantine-color-green-light-color: var(--mantine-color-green-0);--mantine-color-green-outline: var(--mantine-color-green-1);--mantine-color-green-outline-hover: rgba(215, 246, 220, 0.05);--mantine-color-lime-filled: var(--mantine-color-lime-5);--mantine-color-lime-filled-hover: var(--mantine-color-lime-6);--mantine-color-lime-light: rgba(192, 235, 117, 0.15);--mantine-color-lime-light-hover: rgba(192, 235, 117, 0.2);--mantine-color-lime-light-color: var(--mantine-color-lime-0);--mantine-color-lime-outline: var(--mantine-color-lime-1);--mantine-color-lime-outline-hover: rgba(233, 250, 200, 0.05);--mantine-color-yellow-filled: var(--mantine-color-yellow-5);--mantine-color-yellow-filled-hover: var(--mantine-color-yellow-6);--mantine-color-yellow-light: rgba(255, 201, 102, 0.15);--mantine-color-yellow-light-hover: rgba(255, 201, 102, 0.2);--mantine-color-yellow-light-color: var(--mantine-color-yellow-0);--mantine-color-yellow-outline: var(--mantine-color-yellow-1);--mantine-color-yellow-outline-hover: rgba(255, 238, 205, 0.05);--mantine-color-orange-filled: var(--mantine-color-orange-5);--mantine-color-orange-filled-hover: var(--mantine-color-orange-6);--mantine-color-orange-light: rgba(255, 192, 120, 0.15);--mantine-color-orange-light-hover: rgba(255, 192, 120, 0.2);--mantine-color-orange-light-color: var(--mantine-color-orange-0);--mantine-color-orange-outline: var(--mantine-color-orange-1);--mantine-color-orange-outline-hover: rgba(255, 232, 204, 0.05);--app-cta-gradient: linear-gradient(90deg, var(--mantine-color-blue-9) 0%, var(--mantine-color-cyan-7) 100%);--app-color-surface: #2e2e2e;}
:root[data-mantine-color-scheme="light"], :host([data-mantine-color-scheme="light"]){--mantine-color-anchor: var(--mantine-color-text);--mantine-color-dimmed: #495057;--mantine-color-red-light: rgba(224, 40, 41, 0.1);--mantine-color-red-light-hover: rgba(224, 40, 41, 0.12);--mantine-color-red-outline-hover: rgba(224, 40, 41, 0.05);--mantine-color-violet-light: rgba(176, 9, 255, 0.1);--mantine-color-violet-light-hover: rgba(176, 9, 255, 0.12);--mantine-color-violet-outline-hover: rgba(176, 9, 255, 0.05);--mantine-color-indigo-light: rgba(45, 42, 223, 0.1);--mantine-color-indigo-light-hover: rgba(45, 42, 223, 0.12);--mantine-color-indigo-outline-hover: rgba(45, 42, 223, 0.05);--mantine-color-cyan-light: rgba(0, 194, 255, 0.1);--mantine-color-cyan-light-hover: rgba(0, 194, 255, 0.12);--mantine-color-cyan-outline-hover: rgba(0, 194, 255, 0.05);--mantine-color-green-light: rgba(63, 204, 84, 0.1);--mantine-color-green-light-hover: rgba(63, 204, 84, 0.12);--mantine-color-green-outline-hover: rgba(63, 204, 84, 0.05);--mantine-color-yellow-light: rgba(255, 169, 15, 0.1);--mantine-color-yellow-light-hover: rgba(255, 169, 15, 0.12);--mantine-color-yellow-outline-hover: rgba(255, 169, 15, 0.05);--app-color-surface: #f1f3f5;--app-cta-gradient: linear-gradient(90deg, var(--mantine-color-blue-filled) 0%, var(--mantine-color-cyan-5) 100%);}</style><style data-mantine-styles="classes">@media (max-width: 35.99375em) {.mantine-visible-from-xs {display: none !important;}}@media (min-width: 36em) {.mantine-hidden-from-xs {display: none !important;}}@media (max-width: 47.99375em) {.mantine-visible-from-sm {display: none !important;}}@media (min-width: 48em) {.mantine-hidden-from-sm {display: none !important;}}@media (max-width: 61.99375em) {.mantine-visible-from-md {display: none !important;}}@media (min-width: 62em) {.mantine-hidden-from-md {display: none !important;}}@media (max-width: 74.99375em) {.mantine-visible-from-lg {display: none !important;}}@media (min-width: 75em) {.mantine-hidden-from-lg {display: none !important;}}@media (max-width: 87.99375em) {.mantine-visible-from-xl {display: none !important;}}@media (min-width: 88em) {.mantine-hidden-from-xl {display: none !important;}}</style><div style="position:absolute;top:0rem" class=""></div><div style="max-width:var(--container-size-xl);height:100%;min-height:0rem" class=""><style data-mantine-styles="inline">.__m__-_R_5ub_{--grid-gutter:0rem;}</style><div style="height:100%;min-height:0rem" class="m_410352e9 mantine-Grid-root __m__-_R_5ub_"><div class="m_dee7bd2f mantine-Grid-inner" style="height:100%"><style data-mantine-styles="inline">.__m__-_R_rdub_{--col-flex-grow:auto;--col-flex-basis:91.66666666666667%;--col-max-width:91.66666666666667%;}@media(min-width: 48em){.__m__-_R_rdub_{--col-flex-grow:auto;--col-flex-basis:83.33333333333334%;--col-max-width:83.33333333333334%;}}</style><div style="min-width:0rem;height:100%;min-height:0rem;display:flex" class="m_96bdd299 mantine-Grid-col __m__-_R_rdub_"><style data-mantine-styles="inline">.__m__-_R_6qrdub_{margin-top:0rem;padding-inline:var(--mantine-spacing-xs);width:100%;}@media(min-width: 48em){.__m__-_R_6qrdub_{margin-top:var(--mantine-spacing-xl);width:80%;}}@media(min-width: 62em){.__m__-_R_6qrdub_{padding-inline:var(--mantine-spacing-xl);}}</style><div style="margin-inline:auto;max-width:var(--mantine-breakpoint-xl)" class="__m__-_R_6qrdub_"><div style="color:var(--mantine-color-dimmed)" class="m_4451eb3a mantine-Center-root" data-inline="true"><div style="--ti-size:var(--ti-size-xs);--ti-bg:transparent;--ti-color:var(--mantine-color-indigo-light-color);--ti-bd:calc(0.0625rem * var(--mantine-scale)) solid transparent;margin-inline-end:calc(0.125rem * var(--mantine-scale));color:inherit" class="m_7341320d mantine-ThemeIcon-root" data-variant="transparent" data-size="xs"><svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="tabler-icon tabler-icon-lock "><path d="M5 13a2 2 0 0 1 2 -2h10a2 2 0 0 1 2 2v6a2 2 0 0 1 -2 2h-10a2 2 0 0 1 -2 -2v-6"></path><path d="M11 16a1 1 0 1 0 2 0a1 1 0 0 0 -2 0"></path><path d="M8 11v-4a4 4 0 1 1 8 0v4"></path></svg></div><p style="font-size:var(--mantine-font-size-sm)" class="mantine-focus-auto m_b6d8b162 mantine-Text-root">Java: Списки</p></div><h1 style="--title-fw:var(--mantine-h1-font-weight);--title-lh:var(--mantine-h1-line-height);--title-fz:var(--mantine-h1-font-size);margin-bottom:var(--mantine-spacing-xl)" class="m_8a5d1357 mantine-Title-root" data-order="1">Теория: Списки в определении типов</h1><script type="application/ld+json">{"@context":"https://schema.org","@type":"LearningResource","name":"Списки в определении типов","inLanguage":"ru","isPartOf":{"@type":"LearningResource","name":"Java: Списки"},"isAccessibleForFree":"False","hasPart":{"@type":"WebPageElement","isAccessibleForFree":"False","cssSelector":".paywalled"}}</script><div class=""><div style="--alert-color:var(--mantine-color-indigo-light-color);margin-bottom:var(--mantine-spacing-lg);font-size:var(--mantine-font-size-lg)" class="m_66836ed3 mantine-Alert-root" id="mantine-_R_remqrdub_" role="alert" aria-describedby="mantine-_R_remqrdub_-body" aria-labelledby="mantine-_R_remqrdub_-title"><div class="m_a5d60502 mantine-Alert-wrapper"><div class="m_667f2a6a mantine-Alert-icon"><svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" class="tabler-icon tabler-icon-rocket "><path d="M4 13a8 8 0 0 1 7 7a6 6 0 0 0 3 -5a9 9 0 0 0 6 -8a3 3 0 0 0 -3 -3a9 9 0 0 0 -8 6a6 6 0 0 0 -5 3"></path><path d="M7 14a6 6 0 0 0 -3 6a6 6 0 0 0 6 -3"></path><path d="M14 9a1 1 0 1 0 2 0a1 1 0 1 0 -2 0"></path></svg></div><div class="m_667c2793 mantine-Alert-body"><div class="m_6a03f287 mantine-Alert-title"><span id="mantine-_R_remqrdub_-title" class="m_698f4f23 mantine-Alert-label">Полный доступ к материалам</span></div><div id="mantine-_R_remqrdub_-body" class="m_7fa78076 mantine-Alert-message"><div style="--group-gap:var(--mantine-spacing-md);--group-align:center;--group-justify:space-between;--group-wrap:wrap" class="m_4081bf90 mantine-Group-root"><p class="mantine-focus-auto m_b6d8b162 mantine-Text-root">Зарегистрируйтесь и получите доступ к этому и десяткам других курсов</p><a style="--button-height:var(--button-height-xs);--button-padding-x:var(--button-padding-x-xs);--button-fz:var(--mantine-font-size-xs);--button-bg:linear-gradient(45deg, var(--mantine-color-blue-filled) 0%, var(--mantine-color-cyan-filled) 100%);--button-hover:linear-gradient(45deg, var(--mantine-color-blue-filled) 0%, var(--mantine-color-cyan-filled) 100%);--button-color:var(--mantine-color-white);--button-bd:none" class="mantine-focus-auto mantine-active m_77c9d27d mantine-Button-root m_87cf2631 mantine-UnstyledButton-root" data-variant="gradient" data-size="xs" href="/u/new"><span class="m_80f1301b mantine-Button-inner"><span class="m_811560b9 mantine-Button-label">Зарегистрироваться</span></span></a></div></div></div></div></div><div class="paywalled m_d08caa0 mantine-Typography-root"><p>На примере коллекций, мы первый раз столкнулись с типами данных, которые завязаны на интерфейс и имеют несколько его реализаций. Определение свойств и методов с такой структурой отличается от того, как мы до этого работали с примитивными типами.</p>
<p>Рассмотрим пример, когда мы работаем с числами или строками, то определяем свойства и методы соответственно:</p>
<div style="margin-bottom:var(--mantine-spacing-lg)" class="m_e597c321 mantine-CodeHighlight-codeHighlight" dir="ltr"><div class="m_be7e9c9c mantine-CodeHighlight-controls"><button style="--ai-bg:transparent;--ai-hover:transparent;--ai-color:inherit;--ai-bd:none" class="mantine-focus-auto mantine-active m_d498bab7 mantine-CodeHighlight-control m_8d3f4000 mantine-ActionIcon-root m_87cf2631 mantine-UnstyledButton-root" data-variant="none" type="button" aria-label="Copy code"><span class="m_8d3afb97 mantine-ActionIcon-icon"><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" stroke-width="2" stroke="currentColor" fill="none" stroke-linecap="round" stroke-linejoin="round"><path stroke="none" d="M0 0h24v24H0z" fill="none"></path><path d="M8 8m0 2a2 2 0 0 1 2 -2h8a2 2 0 0 1 2 2v8a2 2 0 0 1 -2 2h-8a2 2 0 0 1 -2 -2z"></path><path d="M16 8v-2a2 2 0 0 0 -2 -2h-8a2 2 0 0 0 -2 2v8a2 2 0 0 0 2 2h2"></path></svg></span></button></div><div style="--scrollarea-scrollbar-size:calc(0.25rem * var(--mantine-scale));--sa-corner-width:0px;--sa-corner-height:0px" class="m_f744fd40 mantine-CodeHighlight-scrollarea m_d57069b5 mantine-ScrollArea-root" dir="ltr"><div style="overflow-x:hidden;overflow-y:hidden;overscroll-behavior-inline:none" class="m_c0783ff9 mantine-ScrollArea-viewport" data-scrollbars="xy"><div class="m_b1336c6 mantine-ScrollArea-content"><pre class="m_2c47c4fd mantine-CodeHighlight-pre" style="padding:0"><code class="m_5caae6d3 mantine-CodeHighlight-code">class Point {
private int x;
private int y;
public int getX() {
return x;
}
public void setX(int x) {
this.x = x;
}
public int getY() {
return y;
}
public void setY(int y) {
this.y = y;
}
}</code></pre></div></div></div><button class="mantine-focus-auto m_c9378bc2 mantine-CodeHighlight-showCodeButton m_87cf2631 mantine-UnstyledButton-root" data-hidden="true" type="button">Expand code</button></div>
<p>Здесь мы указываем ровно тот тип, про который мы думаем. Применим такой же подход к спискам. Создадим класс пользователя, у которого есть возможность добавлять друзей:</p>
<div style="margin-bottom:var(--mantine-spacing-lg)" class="m_e597c321 mantine-CodeHighlight-codeHighlight" dir="ltr"><div class="m_be7e9c9c mantine-CodeHighlight-controls"><button style="--ai-bg:transparent;--ai-hover:transparent;--ai-color:inherit;--ai-bd:none" class="mantine-focus-auto mantine-active m_d498bab7 mantine-CodeHighlight-control m_8d3f4000 mantine-ActionIcon-root m_87cf2631 mantine-UnstyledButton-root" data-variant="none" type="button" aria-label="Copy code"><span class="m_8d3afb97 mantine-ActionIcon-icon"><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" stroke-width="2" stroke="currentColor" fill="none" stroke-linecap="round" stroke-linejoin="round"><path stroke="none" d="M0 0h24v24H0z" fill="none"></path><path d="M8 8m0 2a2 2 0 0 1 2 -2h8a2 2 0 0 1 2 2v8a2 2 0 0 1 -2 2h-8a2 2 0 0 1 -2 -2z"></path><path d="M16 8v-2a2 2 0 0 0 -2 -2h-8a2 2 0 0 0 -2 2v8a2 2 0 0 0 2 2h2"></path></svg></span></button></div><div style="--scrollarea-scrollbar-size:calc(0.25rem * var(--mantine-scale));--sa-corner-width:0px;--sa-corner-height:0px" class="m_f744fd40 mantine-CodeHighlight-scrollarea m_d57069b5 mantine-ScrollArea-root" dir="ltr"><div style="overflow-x:hidden;overflow-y:hidden;overscroll-behavior-inline:none" class="m_c0783ff9 mantine-ScrollArea-viewport" data-scrollbars="xy"><div class="m_b1336c6 mantine-ScrollArea-content"><pre class="m_2c47c4fd mantine-CodeHighlight-pre" style="padding:0"><code class="m_5caae6d3 mantine-CodeHighlight-code">import java.util.ArrayList;
class User {
private ArrayList<User> friends;
public ArrayList<User> getFriends() {
return friends;
}
public void setFriends(ArrayList<User> friends) {
this.friends = friends;
}
}</code></pre></div></div></div><button class="mantine-focus-auto m_c9378bc2 mantine-CodeHighlight-showCodeButton m_87cf2631 mantine-UnstyledButton-root" data-hidden="true" type="button">Expand code</button></div>
<p>Пока все выглядит отлично, но посмотрите на возможный пример использования.</p>
<div style="margin-bottom:var(--mantine-spacing-lg)" class="m_e597c321 mantine-CodeHighlight-codeHighlight" dir="ltr"><div class="m_be7e9c9c mantine-CodeHighlight-controls"><button style="--ai-bg:transparent;--ai-hover:transparent;--ai-color:inherit;--ai-bd:none" class="mantine-focus-auto mantine-active m_d498bab7 mantine-CodeHighlight-control m_8d3f4000 mantine-ActionIcon-root m_87cf2631 mantine-UnstyledButton-root" data-variant="none" type="button" aria-label="Copy code"><span class="m_8d3afb97 mantine-ActionIcon-icon"><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" stroke-width="2" stroke="currentColor" fill="none" stroke-linecap="round" stroke-linejoin="round"><path stroke="none" d="M0 0h24v24H0z" fill="none"></path><path d="M8 8m0 2a2 2 0 0 1 2 -2h8a2 2 0 0 1 2 2v8a2 2 0 0 1 -2 2h-8a2 2 0 0 1 -2 -2z"></path><path d="M16 8v-2a2 2 0 0 0 -2 -2h-8a2 2 0 0 0 -2 2v8a2 2 0 0 0 2 2h2"></path></svg></span></button></div><div style="--scrollarea-scrollbar-size:calc(0.25rem * var(--mantine-scale));--sa-corner-width:0px;--sa-corner-height:0px" class="m_f744fd40 mantine-CodeHighlight-scrollarea m_d57069b5 mantine-ScrollArea-root" dir="ltr"><div style="overflow-x:hidden;overflow-y:hidden;overscroll-behavior-inline:none" class="m_c0783ff9 mantine-ScrollArea-viewport" data-scrollbars="xy"><div class="m_b1336c6 mantine-ScrollArea-content"><pre class="m_2c47c4fd mantine-CodeHighlight-pre" style="padding:0"><code class="m_5caae6d3 mantine-CodeHighlight-code">import java.util.List;
var user = new User();
var friends = List.of(new User(), new User());
user.setFriends(friends); // Упс</code></pre></div></div></div><button class="mantine-focus-auto m_c9378bc2 mantine-CodeHighlight-showCodeButton m_87cf2631 mantine-UnstyledButton-root" data-hidden="true" type="button">Expand code</button></div>
<p>Этот код не скомпилируется, потому что тип переменной <code style="margin-bottom:var(--mantine-spacing-lg)" class="m_dfe9c588 mantine-InlineCodeHighlight-inlineCodeHighlight m_e597c321 mantine-CodeHighlight-codeHighlight m_dfe9c588 mantine-InlineCodeHighlight-inlineCodeHighlight">friends</code> будет <code style="margin-bottom:var(--mantine-spacing-lg)" class="m_dfe9c588 mantine-InlineCodeHighlight-inlineCodeHighlight m_e597c321 mantine-CodeHighlight-codeHighlight m_dfe9c588 mantine-InlineCodeHighlight-inlineCodeHighlight">List<User></code>, а не <code style="margin-bottom:var(--mantine-spacing-lg)" class="m_dfe9c588 mantine-InlineCodeHighlight-inlineCodeHighlight m_e597c321 mantine-CodeHighlight-codeHighlight m_dfe9c588 mantine-InlineCodeHighlight-inlineCodeHighlight">ArrayList<User></code> как ожидается. Правильным выходом из этой ситуации будет завязка не на конкретную реализацию <code style="margin-bottom:var(--mantine-spacing-lg)" class="m_dfe9c588 mantine-InlineCodeHighlight-inlineCodeHighlight m_e597c321 mantine-CodeHighlight-codeHighlight m_dfe9c588 mantine-InlineCodeHighlight-inlineCodeHighlight">ArrayList</code>, а на интерфейс <code style="margin-bottom:var(--mantine-spacing-lg)" class="m_dfe9c588 mantine-InlineCodeHighlight-inlineCodeHighlight m_e597c321 mantine-CodeHighlight-codeHighlight m_dfe9c588 mantine-InlineCodeHighlight-inlineCodeHighlight">List</code>.</p>
<div style="margin-bottom:var(--mantine-spacing-lg)" class="m_e597c321 mantine-CodeHighlight-codeHighlight" dir="ltr"><div class="m_be7e9c9c mantine-CodeHighlight-controls"><button style="--ai-bg:transparent;--ai-hover:transparent;--ai-color:inherit;--ai-bd:none" class="mantine-focus-auto mantine-active m_d498bab7 mantine-CodeHighlight-control m_8d3f4000 mantine-ActionIcon-root m_87cf2631 mantine-UnstyledButton-root" data-variant="none" type="button" aria-label="Copy code"><span class="m_8d3afb97 mantine-ActionIcon-icon"><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" stroke-width="2" stroke="currentColor" fill="none" stroke-linecap="round" stroke-linejoin="round"><path stroke="none" d="M0 0h24v24H0z" fill="none"></path><path d="M8 8m0 2a2 2 0 0 1 2 -2h8a2 2 0 0 1 2 2v8a2 2 0 0 1 -2 2h-8a2 2 0 0 1 -2 -2z"></path><path d="M16 8v-2a2 2 0 0 0 -2 -2h-8a2 2 0 0 0 -2 2v8a2 2 0 0 0 2 2h2"></path></svg></span></button></div><div style="--scrollarea-scrollbar-size:calc(0.25rem * var(--mantine-scale));--sa-corner-width:0px;--sa-corner-height:0px" class="m_f744fd40 mantine-CodeHighlight-scrollarea m_d57069b5 mantine-ScrollArea-root" dir="ltr"><div style="overflow-x:hidden;overflow-y:hidden;overscroll-behavior-inline:none" class="m_c0783ff9 mantine-ScrollArea-viewport" data-scrollbars="xy"><div class="m_b1336c6 mantine-ScrollArea-content"><pre class="m_2c47c4fd mantine-CodeHighlight-pre" style="padding:0"><code class="m_5caae6d3 mantine-CodeHighlight-code">import java.util.List;
class User {
private List<User> friends;
public List<User> getFriends() {
return friends;
}
public void setFriends(List<User> friends) {
this.friends = friends;
}
}</code></pre></div></div></div><button class="mantine-focus-auto m_c9378bc2 mantine-CodeHighlight-showCodeButton m_87cf2631 mantine-UnstyledButton-root" data-hidden="true" type="button">Expand code</button></div>
<p>Почему именно так? Фактически в этом и есть смысл интерфейсов. Реализация может поменяться, но код от этого меняться не должен, если интерфейс не меняется. Код выше работает с любой конкретной реализацией:</p>
<div style="margin-bottom:var(--mantine-spacing-lg)" class="m_e597c321 mantine-CodeHighlight-codeHighlight" dir="ltr"><div class="m_be7e9c9c mantine-CodeHighlight-controls"><button style="--ai-bg:transparent;--ai-hover:transparent;--ai-color:inherit;--ai-bd:none" class="mantine-focus-auto mantine-active m_d498bab7 mantine-CodeHighlight-control m_8d3f4000 mantine-ActionIcon-root m_87cf2631 mantine-UnstyledButton-root" data-variant="none" type="button" aria-label="Copy code"><span class="m_8d3afb97 mantine-ActionIcon-icon"><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" stroke-width="2" stroke="currentColor" fill="none" stroke-linecap="round" stroke-linejoin="round"><path stroke="none" d="M0 0h24v24H0z" fill="none"></path><path d="M8 8m0 2a2 2 0 0 1 2 -2h8a2 2 0 0 1 2 2v8a2 2 0 0 1 -2 2h-8a2 2 0 0 1 -2 -2z"></path><path d="M16 8v-2a2 2 0 0 0 -2 -2h-8a2 2 0 0 0 -2 2v8a2 2 0 0 0 2 2h2"></path></svg></span></button></div><div style="--scrollarea-scrollbar-size:calc(0.25rem * var(--mantine-scale));--sa-corner-width:0px;--sa-corner-height:0px" class="m_f744fd40 mantine-CodeHighlight-scrollarea m_d57069b5 mantine-ScrollArea-root" dir="ltr"><div style="overflow-x:hidden;overflow-y:hidden;overscroll-behavior-inline:none" class="m_c0783ff9 mantine-ScrollArea-viewport" data-scrollbars="xy"><div class="m_b1336c6 mantine-ScrollArea-content"><pre class="m_2c47c4fd mantine-CodeHighlight-pre" style="padding:0"><code class="m_5caae6d3 mantine-CodeHighlight-code">import java.util.ArrayList;
var user = new User();
var friends = new ArrayList<User>();
friends.add(new User());
friends.add(new User());
user.setFriends(friends);</code></pre></div></div></div><button class="mantine-focus-auto m_c9378bc2 mantine-CodeHighlight-showCodeButton m_87cf2631 mantine-UnstyledButton-root" data-hidden="true" type="button">Expand code</button></div>
<p>Сегодня мы решили использовать <code style="margin-bottom:var(--mantine-spacing-lg)" class="m_dfe9c588 mantine-InlineCodeHighlight-inlineCodeHighlight m_e597c321 mantine-CodeHighlight-codeHighlight m_dfe9c588 mantine-InlineCodeHighlight-inlineCodeHighlight">ArrayList</code>, а завтра захотели поменять его на <code style="margin-bottom:var(--mantine-spacing-lg)" class="m_dfe9c588 mantine-InlineCodeHighlight-inlineCodeHighlight m_e597c321 mantine-CodeHighlight-codeHighlight m_dfe9c588 mantine-InlineCodeHighlight-inlineCodeHighlight">LinkedList</code>, потому что так будет эффективнее. Код по-прежнему будет работать:</p>
<div style="margin-bottom:var(--mantine-spacing-lg)" class="m_e597c321 mantine-CodeHighlight-codeHighlight" dir="ltr"><div class="m_be7e9c9c mantine-CodeHighlight-controls"><button style="--ai-bg:transparent;--ai-hover:transparent;--ai-color:inherit;--ai-bd:none" class="mantine-focus-auto mantine-active m_d498bab7 mantine-CodeHighlight-control m_8d3f4000 mantine-ActionIcon-root m_87cf2631 mantine-UnstyledButton-root" data-variant="none" type="button" aria-label="Copy code"><span class="m_8d3afb97 mantine-ActionIcon-icon"><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" stroke-width="2" stroke="currentColor" fill="none" stroke-linecap="round" stroke-linejoin="round"><path stroke="none" d="M0 0h24v24H0z" fill="none"></path><path d="M8 8m0 2a2 2 0 0 1 2 -2h8a2 2 0 0 1 2 2v8a2 2 0 0 1 -2 2h-8a2 2 0 0 1 -2 -2z"></path><path d="M16 8v-2a2 2 0 0 0 -2 -2h-8a2 2 0 0 0 -2 2v8a2 2 0 0 0 2 2h2"></path></svg></span></button></div><div style="--scrollarea-scrollbar-size:calc(0.25rem * var(--mantine-scale));--sa-corner-width:0px;--sa-corner-height:0px" class="m_f744fd40 mantine-CodeHighlight-scrollarea m_d57069b5 mantine-ScrollArea-root" dir="ltr"><div style="overflow-x:hidden;overflow-y:hidden;overscroll-behavior-inline:none" class="m_c0783ff9 mantine-ScrollArea-viewport" data-scrollbars="xy"><div class="m_b1336c6 mantine-ScrollArea-content"><pre class="m_2c47c4fd mantine-CodeHighlight-pre" style="padding:0"><code class="m_5caae6d3 mantine-CodeHighlight-code">import java.util.LinkedList;
var user = new User();
var friends = new LinkedList<User>();
friends.add(new User());
friends.add(new User());
user.setFriends(friends);</code></pre></div></div></div><button class="mantine-focus-auto m_c9378bc2 mantine-CodeHighlight-showCodeButton m_87cf2631 mantine-UnstyledButton-root" data-hidden="true" type="button">Expand code</button></div></div><div style="margin-block:var(--mantine-spacing-xl)" class=""><h2 style="--title-fw:var(--mantine-h2-font-weight);--title-lh:var(--mantine-h2-line-height);--title-fz:var(--mantine-h2-font-size);margin-bottom:var(--mantine-spacing-md)" class="m_8a5d1357 mantine-Title-root" data-order="2">Рекомендуемые программы</h2><style data-mantine-styles="inline">.__m__-_R_2mremqrdub_{--carousel-slide-gap:var(--mantine-spacing-xs);--carousel-slide-size:70%;}@media(min-width: 36em){.__m__-_R_2mremqrdub_{--carousel-slide-gap:var(--mantine-spacing-xl);--carousel-slide-size:50%;}}</style><div style="--carousel-control-size:calc(2.5rem * 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7.35036 10.7951 7.15803 10.6148L3.15803 6.86477C2.95657 6.67591 2.94637 6.35949 3.13523 6.15803Z" fill="currentColor" fill-rule="evenodd" clip-rule="evenodd"></path></svg></button><button class="mantine-focus-auto m_64f58e10 mantine-Carousel-control m_87cf2631 mantine-UnstyledButton-root" type="button" data-inactive="true" data-type="next" tabindex="-1"><svg viewBox="0 0 15 15" fill="none" xmlns="http://www.w3.org/2000/svg" style="transform:rotate(-90deg);width:calc(1rem * var(--mantine-scale));height:calc(1rem * var(--mantine-scale));display:block"><path d="M3.13523 6.15803C3.3241 5.95657 3.64052 5.94637 3.84197 6.13523L7.5 9.56464L11.158 6.13523C11.3595 5.94637 11.6759 5.95657 11.8648 6.15803C12.0536 6.35949 12.0434 6.67591 11.842 6.86477L7.84197 10.6148C7.64964 10.7951 7.35036 10.7951 7.15803 10.6148L3.15803 6.86477C2.95657 6.67591 2.94637 6.35949 3.13523 6.15803Z" fill="currentColor" fill-rule="evenodd" clip-rule="evenodd"></path></svg></button></div><div class="m_a2dae653 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