进阶学习：Java 8新特性与实战案例

原创 ╰半橙微兮° 2024-09-25 10:39 104阅读 0赞

Java 8是自Java语言发布以来的一次重大升级，它引入了许多新的特性。以下是一些主要的新特性和实战案例：

1. Lambda表达式：
   - 实战案例：处理集合操作，如filter、map等。
   ```java
   List<String> names = Arrays.asList("John", "Alice", "Bob");
   List<String> evenNames = names.stream() // Stream API
       .filter(name -> name.length() % 2 == 0)) // Lambda expression for filter
       .collect(Collectors.toList()); // Collect and assign to new list
   ```

2. 方法引用来作为参数：
   - 实战案例：创建工具类，提供方便的方法。
   ```java
   // Tool class with methods using method references
   public static class Tools {
       public static String capitalizeFirstLetter(String str) {
           return str.substring(0, 1).toUpperCase() + str.substring(1);
       }

// Similar method for any class, e.g., Person
       public static <T> T getPrivateProperty(T obj, String propertyName) {
           try {
               Field field = obj.getClass()..getDeclaredField(propertyName);
               field.setAccessible(true); // Make accessible (if needed)
               return (T) field.get(obj);
           } catch (NoSuchFieldException | IllegalAccessException e) {
               throw new RuntimeException("Failed to get private property", e);
           }
       }
   }

// Usage in main method
   public static void main(String[] args) {
       Person john = new Person("John Doe", 30);
       System.out.println(Tools.capitalizeFirstLetter(john.getName()))); // Output: "John Doe"

String privateProperty = Tools.getPrivateProperty(person, "age")); // Assuming "person" is instance of Person class
       System.out.println(privateProperty); // Output: the value of "age" property in "person" object
   }
   ```
3. 排序容器（Stream API）：
   - 实战案例：对数据进行排序、分组等操作。
   ```java
   List<String> names = Arrays.asList("Alice", "Bob", "Charlie");

// 1. 排序：升序降序
   List<String> sortedNames;
   if (shouldSortAscending()) {
       sortedNames = names.stream().sorted() // Stream API, using Comparator
           .collect(Collectors.toList()));
   } else if (shouldSortDescending()) {
       sortedNames = names.stream().sorted(Comparator.reverseOrder()))
           .collect(Collectors.toList()));
   }

System.out.println(sortedNames); // Output: [Charlie, Bob, Alice]

// 2. 分组：按字母顺序分组
   Map<String, List<String>> groupedNames;
   groupedNames = names.stream()
       .collect(Collectors.groupingBy(name -> name.toLowerCase())));

for (Map.Entry<String, List<String>>> entry : groupedNames.entrySet()) {
       System.out.println("Group: " + entry.getKey() + ", Names: " + entry.getValue()));
   }

// Output: Group: a, Names: [Alice]
   ```

4. 高级日期时间API（Date-Time API）：
   - 实战案例：处理日期时间相关操作，如计算时间差、格式化输出等。
   ```java
   // 1. 计算时间差
   ZonedDateTime zdt1 = ZonedDateTime.now(); // Current date and time
   ZonedDateTime zdt2 = ZonedDateTime.parse("2023-04-05T12:00Z")); // Given date and time in UTC

Duration durationBetween = Duration.between(zdt1, zdt2)); // Using Duration class for calculation

System.out.println("Time difference between two dates: " + durationBetween.toMinutes()); // Output: Time difference between two dates: 36

// 2. 格式化日期时间
   String formattedDateTime = LocalDateTime.now().format(DateTimeFormatter.ofPattern("yyyy-MM-dd'T'HH:mm:ss.SSSSS"))); // Using DateTimeFormatter for format

System.out.println("Formatted date and time: " + formattedDateTime)); // Output: Formatted date and time: 2023-04-05T12:00.00000000Z
   ```

以上就是Java 8新特性与实战案例的概述，希望对你深入学习Java 8有所帮助。