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《Java 集合框架全解析！从入门到实战，面试 / 开发都用得上！》

news 2025/10/23 12:44:03

第五章：Java集合框架

5.1 集合接口与实现类概述

5.1.1 集合框架体系结构

Java集合框架主要包含两种类型的容器：

Collection：存储单个元素的集合
Map：存储键值对的映射

// 集合框架主要接口关系
Collection
├── List
├── Set
└── QueueMap
├── HashMap
├── TreeMap
└── LinkedHashMap

5.1.2 核心接口介绍

import java.util.*;public class CollectionOverview {public static void main(String[] args) {// Collection接口的基本方法演示Collection<String> collection = new ArrayList<>();// 添加元素collection.add("Java");collection.add("Python");collection.add("C++");// 检查包含System.out.println("包含Java: " + collection.contains("Java"));// 遍历集合for (String language : collection) {System.out.println(language);}// 移除元素collection.remove("C++");System.out.println("移除后: " + collection);}
}

5.2 List、Set、Map的核心区别与使用场景

5.2.1 三大集合类型对比

特性	List	Set	Map
元素顺序	有序	无序(LinkedHashSet有序)	无序(LinkedHashMap有序)
元素唯一性	可重复	唯一	键唯一，值可重复
实现类	ArrayList, LinkedList	HashSet, TreeSet	HashMap, TreeMap
访问方式	索引访问	迭代器访问	键访问

5.2.2 使用场景分析

public class CollectionScenarios {// List使用场景：需要保持插入顺序，允许重复public static void listScenario() {List<String> studentNames = new ArrayList<>();studentNames.add("张三");studentNames.add("李四");studentNames.add("张三"); // 允许重复// 按索引访问System.out.println("第二个学生: " + studentNames.get(1));}// Set使用场景：需要元素唯一性，不关心顺序public static void setScenario() {Set<String> uniqueIds = new HashSet<>();uniqueIds.add("001");uniqueIds.add("002");uniqueIds.add("001"); // 重复元素不会被添加System.out.println("唯一ID集合: " + uniqueIds);}// Map使用场景：键值对映射关系public static void mapScenario() {Map<String, Integer> studentScores = new HashMap<>();studentScores.put("张三", 85);studentScores.put("李四", 92);studentScores.put("王五", 78);// 通过键快速查找值System.out.println("张三的分数: " + studentScores.get("张三"));}
}

5.3 ArrayList、LinkedList、HashSet、HashMap等集合操作

5.3.1 ArrayList详解

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;public class ArrayListDemo {public static void main(String[] args) {// 创建ArrayListArrayList<String> list = new ArrayList<>();// 添加元素list.add("Apple");list.add("Banana");list.add("Orange");list.add(1, "Grape"); // 在指定位置插入// 访问元素System.out.println("第一个元素: " + list.get(0));System.out.println("列表大小: " + list.size());// 修改元素list.set(2, "Mango");// 删除元素list.remove("Apple");list.remove(0);// 排序list.add("Cherry");list.add("Blueberry");Collections.sort(list);System.out.println("排序后: " + list);// 自定义排序Collections.sort(list, Comparator.reverseOrder());System.out.println("逆序: " + list);// 转换为数组String[] array = list.toArray(new String[0]);// 清空列表list.clear();System.out.println("清空后是否为空: " + list.isEmpty());}
}

5.3.2 LinkedList详解

import java.util.LinkedList;public class LinkedListDemo {public static void main(String[] args) {LinkedList<String> linkedList = new LinkedList<>();// 添加元素linkedList.add("First");linkedList.add("Second");linkedList.addFirst("Head"); // 添加到头部linkedList.addLast("Tail");  // 添加到尾部System.out.println("链表: " + linkedList);// 队列操作linkedList.offer("QueueElement"); // 添加到尾部System.out.println("队首: " + linkedList.peek());System.out.println("出队: " + linkedList.poll());// 栈操作linkedList.push("StackElement"); // 压栈System.out.println("栈顶: " + linkedList.peek());System.out.println("出栈: " + linkedList.pop());System.out.println("最终链表: " + linkedList);}
}

5.3.3 HashSet详解

import java.util.HashSet;
import java.util.Arrays;public class HashSetDemo {public static void main(String[] args) {HashSet<String> set = new HashSet<>();// 添加元素set.add("Java");set.add("Python");set.add("C++");set.add("Java"); // 重复元素，不会被添加System.out.println("集合: " + set);System.out.println("集合大小: " + set.size());// 检查包含System.out.println("包含Java: " + set.contains("Java"));// 移除元素set.remove("C++");// 遍历集合for (String element : set) {System.out.println(element);}// 集合运算HashSet<String> otherSet = new HashSet<>(Arrays.asList("Java", "JavaScript", "Go"));// 并集HashSet<String> union = new HashSet<>(set);union.addAll(otherSet);System.out.println("并集: " + union);// 交集HashSet<String> intersection = new HashSet<>(set);intersection.retainAll(otherSet);System.out.println("交集: " + intersection);// 差集HashSet<String> difference = new HashSet<>(set);difference.removeAll(otherSet);System.out.println("差集: " + difference);}
}

5.3.4 HashMap详解

import java.util.HashMap;
import java.util.Map;public class HashMapDemo {public static void main(String[] args) {// 创建HashMapHashMap<String, Integer> map = new HashMap<>();// 添加键值对map.put("Apple", 10);map.put("Banana", 20);map.put("Orange", 15);map.put("Apple", 25); // 更新已存在的键的值System.out.println("HashMap: " + map);// 访问值System.out.println("Apple的数量: " + map.get("Apple"));System.out.println("获取或默认值: " + map.getOrDefault("Grape", 0));// 检查键值存在System.out.println("包含键Banana: " + map.containsKey("Banana"));System.out.println("包含值100: " + map.containsValue(100));// 遍历HashMapSystem.out.println("=== 遍历方式 ===");// 1. 遍历键for (String key : map.keySet()) {System.out.println("Key: " + key + ", Value: " + map.get(key));}// 2. 遍历值for (Integer value : map.values()) {System.out.println("Value: " + value);}// 3. 遍历键值对for (Map.Entry<String, Integer> entry : map.entrySet()) {System.out.println("Key: " + entry.getKey() + ", Value: " + entry.getValue());}// 4. forEach方法map.forEach((key, value) -> System.out.println("Key: " + key + ", Value: " + value));// 移除元素map.remove("Banana");System.out.println("移除后: " + map);// 替换值map.replace("Apple", 30);System.out.println("替换后: " + map);}
}

5.4 迭代器（Iterator）与集合遍历

5.4.1 迭代器基本使用

import java.util.*;public class IteratorDemo {public static void main(String[] args) {List<String> list = Arrays.asList("Java", "Python", "C++", "JavaScript");// 获取迭代器Iterator<String> iterator = list.iterator();// 遍历集合while (iterator.hasNext()) {String element = iterator.next();System.out.println(element);// 安全地移除元素if ("C++".equals(element)) {iterator.remove(); // 在ListIterator中可用}}}
}

5.4.2 ListIterator双向遍历

import java.util.*;public class ListIteratorDemo {public static void main(String[] args) {List<String> list = new ArrayList<>(Arrays.asList("A", "B", "C", "D"));// 获取ListIteratorListIterator<String> listIterator = list.listIterator();System.out.println("正向遍历:");while (listIterator.hasNext()) {int index = listIterator.nextIndex();String element = listIterator.next();System.out.println("Index: " + index + ", Element: " + element);}System.out.println("\n反向遍历:");while (listIterator.hasPrevious()) {int index = listIterator.previousIndex();String element = listIterator.previous();System.out.println("Index: " + index + ", Element: " + element);}// 修改元素listIterator = list.listIterator();if (listIterator.hasNext()) {listIterator.next();listIterator.set("Modified-A"); // 修改当前元素}System.out.println("修改后: " + list);}
}

5.4.3 增强for循环与迭代器

import java.util.*;public class EnhancedForLoop {public static void main(String[] args) {List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);// 增强for循环（底层使用迭代器）System.out.println("增强for循环:");for (Integer num : numbers) {System.out.println(num);}// 等效的迭代器写法System.out.println("\n迭代器写法:");for (Iterator<Integer> it = numbers.iterator(); it.hasNext();) {Integer num = it.next();System.out.println(num);}// 在遍历时修改集合的注意事项List<String> names = new ArrayList<>(Arrays.asList("Tom", "Jerry", "Mike"));// 错误的方式：在增强for循环中修改集合// for (String name : names) {//     if ("Jerry".equals(name)) {//         names.remove(name); // 会抛出ConcurrentModificationException//     }// }// 正确的方式：使用迭代器的remove方法Iterator<String> iterator = names.iterator();while (iterator.hasNext()) {String name = iterator.next();if ("Jerry".equals(name)) {iterator.remove(); // 安全移除}}System.out.println("安全移除后: " + names);}
}

5.5 泛型（Generics）与类型安全

5.5.1 泛型基本概念

import java.util.*;// 自定义泛型类
class GenericBox<T> {private T content;public void setContent(T content) {this.content = content;}public T getContent() {return content;}
}public class GenericsDemo {public static void main(String[] args) {// 不使用泛型的问题List rawList = new ArrayList(); // 原始类型rawList.add("String");rawList.add(123); // 编译时不会报错// 运行时可能抛出ClassCastException// String str = (String) rawList.get(1); // 错误!// 使用泛型保证类型安全List<String> stringList = new ArrayList<>();stringList.add("Hello");// stringList.add(123); // 编译错误!String str = stringList.get(0); // 不需要强制类型转换// 自定义泛型类的使用GenericBox<String> stringBox = new GenericBox<>();stringBox.setContent("Generic String");String content = stringBox.getContent(); // 自动类型转换GenericBox<Integer> integerBox = new GenericBox<>();integerBox.setContent(100);int number = integerBox.getContent();System.out.println("字符串内容: " + content);System.out.println("数字内容: " + number);}
}

5.5.2 泛型方法

import java.util.*;public class GenericMethods {// 泛型方法public static <T> void printArray(T[] array) {for (T element : array) {System.out.print(element + " ");}System.out.println();}// 有界类型参数的泛型方法public static <T extends Comparable<T>> T findMax(T[] array) {if (array == null || array.length == 0) {return null;}T max = array[0];for (T element : array) {if (element.compareTo(max) > 0) {max = element;}}return max;}// 通配符使用public static void processList(List<? extends Number> list) {for (Number number : list) {System.out.println(number.doubleValue());}}public static void main(String[] args) {// 测试泛型方法Integer[] intArray = {1, 2, 3, 4, 5};String[] strArray = {"Apple", "Banana", "Orange"};System.out.println("整数数组:");printArray(intArray);System.out.println("字符串数组:");printArray(strArray);// 测试有界泛型方法Integer maxInt = findMax(intArray);System.out.println("最大整数: " + maxInt);// 测试通配符List<Integer> integerList = Arrays.asList(1, 2, 3);List<Double> doubleList = Arrays.asList(1.1, 2.2, 3.3);System.out.println("处理整数列表:");processList(integerList);System.out.println("处理双精度列表:");processList(doubleList);}
}

5.5.3 类型安全的集合操作

import java.util.*;public class TypeSafeCollections {// 类型安全的集合创建public static void typeSafeDemo() {// 传统方式 - 可能产生类型不安全List unsafeList = new ArrayList();unsafeList.add("String");unsafeList.add(123); // 编译时不报错// 泛型方式 - 类型安全List<String> safeList = new ArrayList<>();safeList.add("String");// safeList.add(123); // 编译错误!// 从安全集合获取元素不需要类型转换String element = safeList.get(0);}// 泛型与集合框架的结合public static void genericCollections() {// 类型安全的MapMap<String, List<Integer>> studentScores = new HashMap<>();// 添加数据studentScores.put("张三", Arrays.asList(85, 90, 78));studentScores.put("李四", Arrays.asList(92, 88, 95));// 类型安全的访问List<Integer> scores = studentScores.get("张三");int firstScore = scores.get(0); // 自动拆箱，不需要强制转换System.out.println("张三的第一个分数: " + firstScore);// 遍历类型安全的Mapfor (Map.Entry<String, List<Integer>> entry : studentScores.entrySet()) {String name = entry.getKey();List<Integer> scoreList = entry.getValue();System.out.println(name + "的分数: " + scoreList);}}// 使用Collections工具类进行类型安全操作public static void collectionsUtility() {List<String> list = new ArrayList<>();// 添加多个元素Collections.addAll(list, "A", "B", "C", "D");// 类型安全的复制List<String> dest = new ArrayList<>(Arrays.asList(new String[list.size()]));Collections.copy(dest, list);System.out.println("复制后的列表: " + dest);// 类型安全的不可修改视图List<String> unmodifiableList = Collections.unmodifiableList(list);// unmodifiableList.add("E"); // 运行时抛出UnsupportedOperationException}public static void main(String[] args) {typeSafeDemo();genericCollections();collectionsUtility();}
}

5.5.4 实际应用示例

import java.util.*;// 学生类
class Student implements Comparable<Student> {private String name;private int score;public Student(String name, int score) {this.name = name;this.score = score;}public String getName() { return name; }public int getScore() { return score; }@Overridepublic int compareTo(Student other) {return Integer.compare(this.score, other.score);}@Overridepublic String toString() {return name + "(" + score + ")";}
}public class PracticalExample {// 使用泛型方法对学生列表进行排序public static <T extends Comparable<T>> void sortStudents(List<T> list) {Collections.sort(list);}// 查找最高分学生public static Student findTopStudent(List<Student> students) {return Collections.max(students);}// 统计分数分布public static Map<String, List<Student>> groupByScoreRange(List<Student> students) {Map<String, List<Student>> result = new HashMap<>();result.put("优秀(90-100)", new ArrayList<>());result.put("良好(80-89)", new ArrayList<>());result.put("及格(60-79)", new ArrayList<>());result.put("不及格(0-59)", new ArrayList<>());for (Student student : students) {int score = student.getScore();if (score >= 90) {result.get("优秀(90-100)").add(student);} else if (score >= 80) {result.get("良好(80-89)").add(student);} else if (score >= 60) {result.get("及格(60-79)").add(student);} else {result.get("不及格(0-59)").add(student);}}return result;}public static void main(String[] args) {// 创建学生列表List<Student> students = Arrays.asList(new Student("张三", 85),new Student("李四", 92),new Student("王五", 78),new Student("赵六", 65),new Student("钱七", 95));// 排序System.out.println("排序前: " + students);sortStudents(students);System.out.println("排序后: " + students);// 查找最高分Student topStudent = findTopStudent(students);System.out.println("最高分学生: " + topStudent);// 分组统计Map<String, List<Student>> scoreGroups = groupByScoreRange(students);System.out.println("\n分数分布:");for (Map.Entry<String, List<Student>> entry : scoreGroups.entrySet()) {System.out.println(entry.getKey() + ": " + entry.getValue());}}
}