2021-04-05

[TOC]

1.时间日期类

java.util.Date

    //构造方法
    public static void main(String[] args) {
        Date date1 = new Date();
        System.out.println(date1);  //当前时间
        Date date2 = new Date(0L);
        System.out.println(date2);  //Thu Jan 01 08:00:00 CST 1970
        Date date3 = new Date(3600000L);
        System.out.println(date3);  //Thu Jan 01 09:00:00 CST 1970
    }
    //getTime() && setTime()
    public static void main(String[] args) {
        Date date1 = new Date();
        Long time1 = date1.getTime();
        System.out.println(time1);  //获取date对象毫秒值

        date1.setTime(0L);  //设置date对象毫秒值
        System.out.println(date1);  //Thu Jan 01 08:00:00 CST 1970
    }

java.text.SimpleDateFormat

    //format()格式化
    public static void main(String[] args) {
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        Date date = new Date();
        String result1 = sdf.format(date);   //2021-04-04 11:03:53
        System.out.println(result1);
    }
    //parse()解析
     public static void main(String[] args) throws ParseException {
        String s = "2021-04-04 11:03:53";
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        Date date = sdf.parse(s);   //Sun Apr 04 11:03:53 CST 2021
        System.out.println(date);
    }

java.time.LocalDateTime(1.8新增)

    public static void main(String[] args) throws ParseException {
        //of() && now()
        LocalDateTime now = LocalDateTime.now();
        System.out.println(now);    //2021-04-04T21:31:23.521
        LocalDateTime localDateTime = LocalDateTime.of(2020, 11, 11, 11, 11, 11);
        System.out.println(localDateTime);  //2020-11-11T11:11:11
        //getDayOfMonth()
        int dayOfMonth = localDateTime.getDayOfMonth();
        System.out.println(dayOfMonth); //11
        //toLocalDate()转换为年月日
        LocalDate localDate = localDateTime.toLocalDate();
        //toLocalTime()转换为时分秒
        LocalTime localTime = localDateTime.toLocalTime();
        System.out.println(localDate); //2020-11-11
        System.out.println(localTime); //11:11:11
    }

    public static void main(String[] args) {
        //format
        LocalDateTime localDateTime = LocalDateTime.now();
        DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
        String s = localDateTime.format(dateTimeFormatter);
        System.out.println(s);
        //parse
        String s1 = "2021-04-04 21:52:00";
        LocalDateTime parse = LocalDateTime.parse(s1, dateTimeFormatter);
        System.out.println(parse);
    }

     public static void main(String[] args) {
        //plus && minus && with
        LocalDateTime localDateTime = LocalDateTime.now();
        LocalDateTime newlocalDateTime1 = localDateTime.plusYears(1);
        LocalDateTime newlocalDateTime2 = localDateTime.minusYears(1);
        LocalDateTime newlocalDateTime3 = localDateTime.withYear(2099);
        //Period.between 两个日期相差的天数
        Period period = Period.between(newlocalDateTime1.toLocalDate(), newlocalDateTime3.toLocalDate());
        System.out.println(period); //P-79Y
        System.out.println(period.getYears()); //79
        //Duration.between 两个日期相差的秒数
        Duration duration = Duration.between(newlocalDateTime1, newlocalDateTime3);
        System.out.println(duration); //PT674976H
        System.out.println(duration.getSeconds()); //2429913600
    }

2.异常

异常体系

graph TD;
    Throwable-->Error;
    Throwable-->Exception;
    Exception-->RuntimeException及其子类;
    Exception-->除RuntimeException之外的所有异常
    

3.集合

集合类体系

graph TD;   
    集合-->|单列| Collection;
    集合-->|单列| Map;
    Collection-->|可重复| List;
    Collection-->|不可重复| Set;
    Map-->HashMap;
    Map-->TreeMap;
    List-->ArrayList;
    List-->LinkedList;
    Set-->HashSet;
    Set-->TreeSet;
    style ArrayList fill:white;
    style LinkedList fill:white;
    style HashSet fill:white;
    style TreeMap fill:white;
    style HashMap fill:white;
    style TreeSet fill:white;
    subgraph  
        接口
        实现类
        style 实现类 fill:white;
    end

collection常见成员方法

迭代器与增强for

    public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<>();
        list.add("aaaa");
        list.add("bbbb");
        list.add("cccc");
        list.add("dddd");
        Iterator<String> it = list.iterator();
        while (it.hasNext()) {
            String s = it.next();
            if ("bbbb".equals(s)) {
                it.remove();
            }
        }
        System.out.println(list);
        for (String s : list) {
            System.out.println(s);
        }
    }