Java集合框架实战HashMap与HashSet的使用案例

public class WordCounter {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入一段文本:");
        String text = scanner.nextLine();
        // 使用HashMap统计单词出现次数
        HashMap<String, Integer> wordCount = new HashMap<>();
        // 分割文本为单词（按空格和标点符号分割）
        String[] words = text.split("[\\s\\p{Punct}]+");
        for (String word : words) {
            if (!word.isEmpty()) {
                String lowerWord = word.toLowerCase(); // 不区分大小写
                wordCount.put(lowerWord, wordCount.getOrDefault(lowerWord, 0) + 1);
            }
        }
        // 输出统计结果
        System.out.println("\n单词统计结果:");
        for (Map.Entry<String, Integer> entry : wordCount.entrySet()) {
            System.out.println(entry.getKey() + ": " + entry.getValue());
        }
    }
}

String[] words = text.split("[\\s\\p{Punct}]+");

wordCount.put(lowerWord, wordCount.getOrDefault(lowerWord, 0) + 1);

// 传统方式
if (wordCount.containsKey(lowerWord)) {
    wordCount.put(lowerWord, wordCount.get(lowerWord) + 1);
} else {
    wordCount.put(lowerWord, 1);
}
// 现代方式（推荐）
wordCount.put(lowerWord, wordCount.getOrDefault(lowerWord, 0) + 1);

HashMap<String, Integer> wordCount = new HashMap<>(expectedSize);

Arrays.stream(words)
      .parallel()
      .forEach(word -> {
          // 统计逻辑
      });

public class DeduplicationAndSorting {
    public static void main(String[] args) {
        // 创建包含重复元素的整数列表
        ArrayList<Integer> numbers = new ArrayList<>(Arrays.asList(
            5, 2, 8, 2, 1, 9, 5, 3, 7, 1, 4, 6, 8, 3
        ));
        System.out.println("原始列表: " + numbers);
        // 使用HashSet去重
        HashSet<Integer> uniqueNumbers = new HashSet<>(numbers);
        System.out.println("去重后: " + uniqueNumbers);
        // 使用TreeSet排序（自动排序）
        TreeSet<Integer> sortedNumbers = new TreeSet<>(uniqueNumbers);
        System.out.println("排序后: " + sortedNumbers);
        // 或者使用Collections.sort()方法
        ArrayList<Integer> sortedList = new ArrayList<>(uniqueNumbers);
        Collections.sort(sortedList);
        System.out.println("使用Collections.sort()排序: " + sortedList);
    }
}

class Student {
    private String id;
    private String name;
    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Student student = (Student) o;
        return Objects.equals(id, student.id);
    }
    @Override
    public int hashCode() {
        return Objects.hash(id);
    }
}

// 降序排序
TreeSet<Integer> descendingSet = new TreeSet<>(Collections.reverseOrder());
descendingSet.addAll(uniqueNumbers);
// 自定义对象排序
TreeSet<Student> studentSet = new TreeSet<>(
    Comparator.comparing(Student::getName)
              .thenComparing(Student::getAge)
);