java8 List集合的排序，求和，取最大值，按照條件過濾

public class Java8Test {

    public static void main(String[] args) {

        Person p1 = new Person("麻子", 31);
        Person p2 = new Person("李四", 20);
        Person p3 = new Person("王五", 26);

        List<Person> personList = new ArrayList<Person>();
        personList.add(p1);
        personList.add(p2);
        personList.add(p3);

        //java8遍歷
        personList.forEach(p -> System.out.println(p.getAge()));
        //按照person的 age進行排序
        //方法一
        personList.sort((o1, o2) -> o1.getAge().compareTo(o2.getAge())); //正序
        personList.sort((o1, o2) -> o2.getAge().compareTo(o1.getAge())); //倒序
        //方法二
        personList.sort(Comparator.comparing(Person::getAge)); // 正序
        personList.sort(Comparator.comparing(Person::getAge).reversed()); // 倒序
        //遍歷
        personList.forEach(p -> System.out.println(p.getAge()));

        System.out.println("========================================");

        //獲取年齡最大的Person
        Person maxAgePerson = personList.stream().max(Comparator.comparing(Person::getAge)).get();
        System.out.println(maxAgePerson.getAge());

        System.out.println("========================================");

        //獲取年齡最小的Person
        Person minAgePerson = personList.stream().min(Comparator.comparing(Person::getAge)).get();
        System.out.println(minAgePerson.getAge());

        //過濾出年齡是20的person，想過濾出什麼條件的均可以
        List<Person> personList1 = personList.stream().filter(person -> person.getAge() == 20).collect(Collectors.toList());

        //統計出年齡等於20的個數
        long count = personList.stream().filter(person -> person.getAge() == 20).count();

        //得到年齡的平均值
        double asDouble = personList.stream().mapToInt(person -> person.getAge()).average().getAsDouble();

        //得到年齡的求和
        int sum = personList.stream().mapToInt(person -> person.getAge()).sum();

    }
}