JAVA8新特性

时间日期类 private LocalDate

//        LocalDate localDate=LocalDate.now();
//        System.out.println(localDate);  2021-3-19
//        LocalTime time=LocalTime.now();  11：58：40.031
//        LocalDateTime dateTime=LocalDateTime.now();2021-2-18T19:19:40.031

//        LocalDate date=LocalDate.of(2021,3,17);  指定整数组成时间

//        LocalDate date1=LocalDate.parse("2021-03-16");  将字符序列转成日期，中间必须用-两位数
//        date1.getYear();
          data1.getMonthValue();提取年月日
//        date1.getDayOfWeek();

//        //时间戳 毫秒数
        System.out.println(Instant.now().toEpochMilli());

        //时间格式化
//        DateTimeFormatter formatter=DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
//        System.out.println(formatter.format(LocalDateTime.now())); 2021-03-19 12：01：40


//        String[]names={"zhang","li","yang"};
//        Arrays.asList(names).forEach(System.out::println);
//asList转化为集合  forEach放的consumer接口
      //  Consumer 消费型接口  <T>      接受参数输出   都是函数式接口
//        Consumer <Integer> consumer1=Demo01::printData;
//        consumer1.accept(5);

      //  Supplier 供给型接口  获取
          Supplier<Integer>supplier=()-> new Random().nextInt(10);
          System.out.println(supplier.get());

          Supplier<Integer>supplier1=new Random()::nextInt;
          System.out.println(supplier1.get());

       // Predicate 断言  布尔值
        Predicate<Integer>predicate=(x) -> x>0;
        predicate.test(5);
        

      // Function 函数 执行  第一个参数是参数类型 第二个参数返回值类型
        Function<String,Integer>function=(str)->str.length();
        function.apply("sda");

       Function<Integer,Integer>function=(num)->num*num;
        function.apply(5);

 //  Consumer 消费型接口 一条语句实现

//    public static void printData(Integer x){
//        System.out.println(x+1);
//    }

@FunctionalInterface 函数式接口
//一个抽象方法
public interface Aritst {
    void sing(String singer);
    default void dance(){};
    default void paint(){};
    static void test(){
        System.out.println();
    }

接口可以加default实现或者加static静态方法

@FunctionalInterface注解只能包含
函数式接口只有一个抽象方法

   Aritst aritst =  (singer) -> {    //只能实现一个抽象接口
//            System.out.println(singer);
//            System.out.println(singer.length());
//        };
//        aritst.sing("a");

public class someOne implements Aritst {

    @Override
    public void sing(String name) {

    }

//    @Override
//    public void dance() {
//
//    }
//
//    @Override
//    public void paint() {
//
//    }
}

public class Calc {
//    int calc(int x int y){
//        return x+y;
//    }
//    (x,y)->{x+y}

函数式接口可以用：

lambda表达式->  是一个匿名函数，允许把一个函数作为参数进行传递
（参数1，参数2。。。）->{方法体}  只能用在函数式接口


方法的引用：：
方法的引用是用来访问类或者实例已经存在的方法或者构造方法
前提是，lambda表达式方法体只有一条代码

optional 非空验证 对普通对象的包装  私有


public class Demo {
    public Demo() {
    }

    public static void main(String[] args) {
      //  Person person = null; 用get抛出异常
        Person person1 = new Person();
        person1.setName((String)null);

        Optional<Person> op = Optional.ofNullable(person1); 不能为空ofNullable
        op.get();获取值
        System.out.println("----------------");

        PrintStream var10001 = System.out;
        op.ifPresent(var10001::println); 

     //orElse orElseGet当值不存在时返回默认值
        System.out.println(((Person)op.orElse(person1)).getName());
        System.out.println(((Person)op.orElseGet(() -> {
            return person1;
        })).getName());


        Street street = new Street("");
        street.setName("宾水西道");
        City city = new City();
        city.setStreet(street);
        Country country = new Country();
        country.setCity(city);
        Address address = new Address;
        address.setCountry(country);
        person1.setAddress(address);
        System.out.println(getStreetName(op));
        System.out.println("*******");

        System.out.println(op.filter((p) -> {  filter返回断言接口
            return Optional.of(p.getName()).isPresent();
        }));
    }

    public static String getStreetName(Optional<Person> p) {
        return (String)p.map((p1) -> {
            return p1.getAddress();
        }).map((a) -> {
            return a.getCountry();
        }).map((c) -> {
            return c.getCity();
        }).map((c) -> {
            return c.getStreet();
        }).map((s) -> {
            return s.getName();
        }).orElse("未知地址");
    }
}

public class Address {
    private Country country;

    public Address() {
    }

    public Country getCountry() {
        return this.country;
    }

    public void setCountry(Country country) {
        this.country = country;
    }
}

public class City {
    private Street street;

    public Street getStreet() {
        return street;
    }

    public void setStreet(Street street) {
        this.street = street;
    }
}

public class Country {
    private City city;

    public Country() {
    }

    public City getCity() {
        return this.city;
    }

    public void setCity(City city) {
        this.city = city;
    }
}


public class Street {
    private String name;

    public String getName() {
        return this.name;
    }

    public Street(String name) {
        this.name = name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String toString() {
        return "Street{name='" + this.name + '\'' + '}';
    }
}

public class Person {
    private String name;
    private Address address = null;

    public Person() {
    }

    public Address getAddress() {
        return this.address;
    }

    public void setAddress(Address address) {
        this.address = address;
    }

    public String getName() {
        return this.name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

stream 和集合一起，对集合或者数组中的数据  数据源：可以是数组或集合

public class Demo {
    public Demo() {
    }

    public static void main(String[] args) {
        List<Street> list = new ArrayList();
        list.add(new Street("宾水西道"));
        list.add(new Street("工西路"));
        list.add(new Street("ab"));

        Stream<Street> stream = list.stream();list获取流
        stream.forEach(System.out::println);
        String[] names ={"zhangsan", "lisi"};
      
        Arrays.stream(names).forEach(System.out::println);

        Stream var10000 = Arrays.stream(names);
        PrintStream var10001 = System.out;
        var10000.forEach(var10001::println);

        Stream<Integer> s1 = Stream.of(10, 20, 30);

        s1.forEach(System.out::println);

        System.out.println("--------generate无限流--------");

        s1=Stream.generate(()->new Random().nextInt(10));

        System.out.println("--------iterate无限流--------");

        s1=Stream.iterate(0,x->x+10);

        System.out.println("---------filter-------");断言

list.stream().filter((s)->s.getName().length()>3).forEach(System.out::println);

list.stream().skip(2).forEach(System.out::println); 跳过skip

list.stream().map((s)->s.getName().length()).forEach(System.out::println);映射

list.stream().sorted(Comparator.comparingInt((s)->s.getName().length())).forEach(System.out::println);

}sort Comparator接口

NIO paths类

public class Demo {
    public Demo() {
    }

Path path= Paths.get("filess","abc.txt");
if (!Files.exists(path));
try {
    Files.createDirectory(Paths.get("filess"));

Files.createFile(path);

} catch (IOException e) {
    e.printStackTrace();
}

try {
    Files.write(path,"今天上了9小时课".getBytes());写
} catch (IOException e) {
    e.printStackTrace();
}
try {
   List<String>list= Files.readAllLines(path);读
   list.stream().forEach(System.out::println);
} catch (IOException e) {
    e.printStackTrace();
}
 
channel通道  写到buffer里
FileChannel fileChannel=new FileOutputStream("filess/abc.txt").getChannel();文件通道
fileChannel.write(ByteBuffer.wrap("hahha".getBytes()));把字符数组转成字符缓冲流
fileChannel.close();

buffer
ByteBuffer buffer=ByteBuffer.allocate(1024);分配空间
fileChannel= new  FileInputStream("filess/abc.txt").getChannel();
fileChannel.read(buffer);
buffer.flip();从第一个元素读
while (buffer.hasRemaining()){有没有继续的状态
    System.out.println(buffer.get());
}

posted @ 2021-03-21 13:24 YangYuJia 阅读(6) 评论(0) 收藏举报

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