Java8 十大新特性

1、lambda表达式

1）对象 =（变量…） ->{
方法实现
}
2）实例：

public class LambdaDemo{
    public static void main(String[] args){
        System.out.println("kk");


        Runnable r =()->{
            int i = 0;
            System.out.println("i="+(i++));
        };

        Action action = (String content)->{
            System.out.println(content);
        };
        action.execute("haha");
    }

    static  interface  Action{
        void execute(String content);
    }
}

2、Stream泛型接口，有过滤功能

1）创建一个元素Person集合：people使用Stream 和 forEach显示该集合所以元素

public class Person {
    public static enum Sex {
        FEMALE, MALE;
    }

    public String name;
    public int age;
    public Sex sex;

    public Person(String name, int age, Sex sex) {
        this.name = name;
        this.age = age;
        this.sex = sex;
    }

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", sex=" + sex +
                '}';
    }
}

打印所有信息

public class StreamDemo {
    public static void main(String[] args){
        List<Person> persons = initPersons();
        Stream<Person> stream = persons.stream();
        stream.filter(p -> p.sex == Person.Sex.FEMALE);
        stream.forEach(
                p -> System.out.println(p.toString())
        );
    }

    public static List<Person> initPersons(){
        List<Person> persons = new ArrayList<Person>();
        Person person = new Person("tom", 22 , Person.Sex.FEMALE);
        persons.add(person);
        person = new Person("jack", 23 , Person.Sex.FEMALE);
        persons.add(person);
        person = new Person("lily", 24 , Person.Sex.FEMALE);
        persons.add(person);
        person = new Person("stone", 25 , Person.Sex.FEMALE);
        persons.add(person);
        return  persons;
    }

}

3、Stream求平均值

public class StreamDemo {

    public static void main(String[] args) {
        List<Person> persons = initPersons();
        Stream<Person> stream = persons.stream();
        double avgAge = stream.filter(p -> p.age > 18)
        .filter(p -> p.name.indexOf("tom")>=0)
        .mapToDouble(p -> p.age)
        .average()
        .getAsDouble();
        System.out.println(avgAge);     
    }

    public static List<Person> initPersons() {
        List<Person> persons = new ArrayList<Person>();
        Person person = new Person("tom", 22, Person.Sex.FEMALE);
        persons.add(person);
        person = new Person("jack", 23, Person.Sex.FEMALE);
        persons.add(person);
        person = new Person("lily", 24, Person.Sex.FEMALE);
        persons.add(person);
        person = new Person("stone", 25, Person.Sex.FEMALE);
        persons.add(person);
        return persons;
    }
}

4、LocateDate 与 LocateTime的用法

1)LocateDate.now():系统日期
2)LocateDate.of(int year, int month, int dayOfMonth):按指定日期创建LocateDate
3)getYear():返回日期中的年份
4)getMonth():返回日期中的月份
5)getDayOfMonth():返回月份中的日

public class LocateDateDemo {
    public static void main(String[] args) {
        LocalDate date = LocalDate.now();
        System.out.println(date.toString());
        System.out.println(date.getYear() + "年");
        System.out.println(date.getMonth()+ "月");
        System.out.println(date.getDayOfMonth() + "日");

        LocalTime time = LocalTime.now();
        System.out.println(time.getHour());
        System.out.println(time.getMinute());
        System.out.println(time.getSecond());
        System.out.println(time.toString());

        LocalDateTime dateTime = LocalDateTime.now();
        System.out.println(dateTime.toString());
        System.out.println(dateTime.getYear() + "年");
        System.out.println(dateTime.getMonth()+ "月");
        System.out.println(dateTime.getDayOfMonth() + "日"); 
        System.out.println(dateTime.getHour());
        System.out.println(dateTime.getMinute());
        System.out.println(dateTime.getSecond());
    }
}

5、DateTimeFormatter

public class DateFormatterDemo {

    public static void main(String[] args) {
        DateTimeFormatter dtf = DateTimeFormatter.ofPattern("yyyy-MM-dd:HH:mm:ss");
        LocalDateTime dateTime = LocalDateTime.parse("2018-11-31:11:12:13",dtf);
        System.out.println(dateTime.toString());
    }
}

6、ZonedDateTime系统时间

LocalDateTime dateTime = LocalDateTime.parse("2018-11-31:11:12:13",dtf);
ZonedDateTime dt = ZonedDateTime.now();
String formatDate = dt.format(dtf);
System.out.println(formatDate);