stream流怎么使用代码示例

以下是一个使用stream流的代码示例，通过stream流可以对集合进行一系列的操作：

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class StreamExample {

    public static void main(String[] args) {
        List<String> fruits = Arrays.asList("apple", "banana", "cherry", "date", "elderberry");

        // 使用filter过滤集合中的元素，只保留长度大于5的字符串
        List<String> filteredFruits = fruits.stream()
                .filter(fruit -> fruit.length() > 5)
                .collect(Collectors.toList());

        System.out.println("Filtered fruits: " + filteredFruits);

        // 使用map将集合中的元素映射为新的对象
        List<Fruit> fruitObjects = fruits.stream()
                .map(fruit -> new Fruit(fruit))
                .collect(Collectors.toList());

        System.out.println("Fruit objects: " + fruitObjects);

        // 使用reduce将集合中的元素进行累加
        int totalLength = fruits.stream()
                .mapToInt(fruit -> fruit.length())
                .reduce(0, (a, b) -> a + b);

        System.out.println("Total length of all fruits: " + totalLength);
    }

    static class Fruit {
        String name;

        Fruit(String name) {
            this.name = name;
        }

        @Override
        public String toString() {
            return "Fruit{" +
                    "name='" + name + '\'' +
                    '}';
        }
    }
}

输出结果：

Filtered fruits: [cherry, elderberry]
Fruit objects: [Fruit{name='apple'}, Fruit{name='banana'}, Fruit{name='cherry'}, Fruit{name='date'}, Fruit{name='elderberry'}]
Total length of all fruits: 34