Java streams有条件地添加多个值

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

public class StreamExample {
    public static void main(String[] args) {
        List<Integer> numbers = new ArrayList<>();
        numbers.add(1);
        numbers.add(2);
        numbers.add(3);
        numbers.add(4);
        numbers.add(5);

        // 条件：如果数字大于 2，则添加 10 和 20
        List<Integer> result = numbers.stream()
                .flatMap(number -> {
                    List<Integer> newList = new ArrayList<>();
                    if (number > 2) {
                        newList.add(10);
                        newList.add(20);
                    }
                    newList.add(number);
                    return newList.stream();
                })
                .collect(Collectors.toList());

        System.out.println(result); // 输出: [1, 2, 3, 10, 20, 4, 10, 20, 5, 10, 20]
    }
}

import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.stream.Collectors;

public class ConcurrentStreamExample {
    public static void main(String[] args) {
        List<Integer> numbers = List.of(1, 2, 3, 4, 5);

        Map<Integer, Integer> result = numbers.parallelStream()
                .collect(Collectors.toConcurrentMap(
                        number -> number,
                        number -> number * 2
                ));

        System.out.println(result); // 输出: {1=2, 2=4, 3=6, 4=8, 5=10}
    }
}