在Java8中使用StreamAPI的实际应用

List<String> fruits = Arrays.asList("Apple", "Banana", "Cherry", "Date");
fruits.stream()
      .filter(fruit -> fruit.startsWith("A"))
      .forEach(System.out::println); // 输出: Apple

List<String> names = Arrays.asList("Alice", "Bob", "Charlie", "David");
// 中间操作（filter, map）和终端操作（forEach）
names.stream()
     .filter(name -> name.length() > 3)  // 中间操作
     .map(String::toUpperCase)          // 中间操作
     .forEach(System.out::println);     // 终端操作

List<Product> products = Arrays.asList(
    new Product("Laptop", 999.99, "Electronics"),
    new Product("Desk", 299.99, "Furniture"),
    new Product("Phone", 599.99, "Electronics")
);
// 获取所有电子类产品名称（价格>500）
List<String> expensiveElectronics = products.stream()
    .filter(p -> p.getCategory().equals("Electronics"))
    .filter(p -> p.getPrice() > 500)
    .map(Product::getName)
    .collect(Collectors.toList());
System.out.println(expensiveElectronics); // [Laptop, Phone]

int[] numbers = {3, 5, 7, 11, 13, 17, 19};
IntSummaryStatistics stats = Arrays.stream(numbers)
    .summaryStatistics();
System.out.println("Max: " + stats.getMax());      // 19
System.out.println("Min: " + stats.getMin());      // 3
System.out.println("Avg: " + stats.getAverage());  // 10.714...

Map<String, List<Product>> productsByCategory = products.stream()
    .collect(Collectors.groupingBy(Product::getCategory));
// 按价格分区（高价/低价）
Map<Boolean, List<Product>> partitionedProducts = products.stream()
    .collect(Collectors.partitioningBy(p -> p.getPrice() > 500));

long count = products.parallelStream()
    .filter(p -> p.getPrice() > 300)
    .count();
System.out.println("Expensive products: " + count);

List<List<String>> nestedNames = Arrays.asList(
    Arrays.asList("Alice", "Bob"),
    Arrays.asList("Charlie", "David")
);
List<String> allNames = nestedNames.stream()
    .flatMap(Collection::stream)
    .collect(Collectors.toList());
// 结果: [Alice, Bob, Charlie, David]

Optional<Product> firstExpensive = products.stream()
    .filter(p -> p.getPrice() > 500)
    .findFirst();

String joinedNames = products.stream()
    .map(Product::getName)
    .collect(Collectors.joining(", ", "[", "]"));
// 示例结果: [Laptop, Desk, Phone]