进阶学习：Java 8新特性与实战案例-蒲公英云

进阶学习：Java 8新特性与实战案例

原创 ╰半橙微兮° 2024-09-25 10:39 212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：

Lambda表达式：

实战案例：处理集合操作，如filter、map等。

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

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 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

}
```

排序容器（Stream API）：
- 实战案例：对数据进行排序、分组等操作。
```java
List names = Arrays.asList(“Alice”, “Bob”, “Charlie”);
// 1. 排序：升序降序
List 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> groupedNames;
groupedNames = names.stream()
```
.collect(Collectors.groupingBy(name -> name.toLowerCase())));
```
for (Map.Entry>> entry : groupedNames.entrySet()) {
```
System.out.println("Group: " + entry.getKey() + ", Names: " + entry.getValue()));
```
}

// Output: Group: a, Names: [Alice]
```
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’HHss.SSSSS”))); // Using DateTimeFormatter for format

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