java8 复合类型对象的List集合的排序，求和，取最大值，按照条件过滤

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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遍历         personList.forEach(p -> System.out.println(p.getAge()));         //按照person的 age进行排序         //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         //遍历         personList.forEach(p -> System.out.println(p.getAge()));           System.out.println("========================================");           //获取年龄最大的Person         Person maxAgePerson = personList.stream().max(Comparator.comparing(Person::getAge)).get();         System.out.println(maxAgePerson.getAge());           System.out.println("========================================");           //获取年龄最小的Person         Person minAgePerson = personList.stream().min(Comparator.comparing(Person::getAge)).get();         System.out.println(minAgePerson.getAge());           //过滤出年龄是20的person，想过滤出什么条件的都可以         List<Person> personList1 = personList.stream().filter(person -> person.getAge() ==          20).collect(Collectors.toList());           //统计出年龄等于20的个数         long count = personList.stream().filter(person -> person.getAge() == 20).count();           //获得年龄的平均值         double asDouble = personList.stream().mapToInt(person -> person.getAge()).average().getAsDouble();           //获得年龄的求和         int sum = personList.stream().mapToInt(person -> person.getAge()).sum();       } }