Java------常用类（二）

import org.junit.Test;

import java.io.UnsupportedEncodingException;
import java.util.Arrays;


public class StringTest1 {

    
    @Test
    public void test1(){
        String str1 = "123";//数据存储在常量池中
//        int num = (int)str1;//错误的
        int num = Integer.parseInt(str1);

        String str2 = String.valueOf(num);   //"123
        String str3 = num + "";//有变量名参与，那么 String str3数据存储在堆里
        System.out.println(str2);//123
        System.out.println(str1 == str3);   //false
    }



        @Test
        
        public void test2(){
            String str1 = "123";
//        int num = (int)str1;//错误的
            int num = Integer.parseInt(str1);

            String str2 = String.valueOf(num);   //"123
            String str3 = num + "";
            System.out.println(str2);//123
            System.out.println(str1 == str3);   //false
        }
    @Test
    
   

    public void test3(){
        String str1 = "abc123"; //题目： a21cb3

        char[] charArray = str1.toCharArray();
        for (int i = 0; i < charArray.length; i++) {
            System.out.println(charArray[i]);
        }

        char[] arr = new char[]{'h','e','l','l','o'};
        String str2 = new String(arr);
        System.out.println(str2);
    }
    @Test
    
    public void test4() throws UnsupportedEncodingException {
        String str1 = "abc123重工";
        byte[] bytes = str1.getBytes();//使用默认的字符编码集,进行转换
        System.out.println(Arrays.toString(bytes));

        byte[] gbks = str1.getBytes("gbk");//使用gbk字符集进行编码。
        System.out.println(Arrays.toString(gbks));

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

        String str2 = new String(bytes);//使用默认的字符集，进行解码。
        System.out.println(str2);

        String str3 = new String(gbks);
        System.out.println(str3);//出现乱码。原因：编码集和解码集不一致！

        String str4 = new String(gbks,"gbk");
        System.out.println(str4);//没有出现乱码。原因：编码集和解码集一致！

    }
    @Test
    public void sss(){
        final String s1 = "awdq";
        String s2 = s1 + "qfqi";
        String s3 = "awdqqfqi";
        System.out.println(s3 == s2);
        //s1此时是个常量，而不是变量，因为加了fianl
    }
}

package doy2;


import org.junit.Test;


public class StringExer {

    // 第1题
    public String myTrim(String str) {
        if (str != null) {
            int start = 0;// 用于记录从前往后首次索引位置不是空格的位置的索引
            int end = str.length() - 1;// 用于记录从后往前首次索引位置不是空格的位置的索引

            while (start < end && str.charAt(start) == ' ') {
                start++;
            }

            while (start < end && str.charAt(end) == ' ') {
                end--;
            }
            if (str.charAt(start) == ' ') {
                return "";
            }

            return str.substring(start, end + 1);
        }
        return null;
    }

    @Test
    public void testMyTrim() {
        String str = "   a   ";
        // str = " ";
        String newStr = myTrim(str);
        System.out.println("---" + newStr + "---");
    }
}

package doy3;


import org.junit.Test;



public class StringBufferBuilderTest {
    
    @Test
    public void test1(){
        StringBuffer sb1 = new StringBuffer("abc");
        sb1.setCharAt(0,'m');
        System.out.println(sb1);

        StringBuffer sb2 = new StringBuffer();
        System.out.println(sb2.length());   //0
    }
}

package doy3;


import org.junit.Test;


public class StringBufferBuilderTest1 {

    
    @Test
    public void test2(){
        StringBuffer s1 = new StringBuffer("abc");
        s1.append(1);
        s1.append('1');
        System.out.println(s1);
//        s1.delete(2,4);
//        s1.replace(2,4,"hello");
//        s1.insert(2,false);
//        s1.reverse();
        String s2 = s1.substring(1,3);
        System.out.println(s1);
        System.out.println(s1.length());
        System.out.println(s2);
    }
}

package doy3;


import org.junit.Test;


public class StringBufferBuilderTest2 {

    
    @Test
    public void test3(){
        //初始设置
        long startTime = 0L;
        long endTime = 0L;
        String text = "";
        StringBuffer buffer = new StringBuffer("");
        StringBuilder builder = new StringBuilder("");
        //开始对比
        startTime = System.currentTimeMillis();
        for (int i = 0; i < 20000; i++) {
            buffer.append(String.valueOf(i));
        }
        endTime = System.currentTimeMillis();
        System.out.println("StringBuffer的执行时间：" + (endTime - startTime));

        startTime = System.currentTimeMillis();
        for (int i = 0; i < 20000; i++) {
            builder.append(String.valueOf(i));
        }
        endTime = System.currentTimeMillis();
        System.out.println("StringBuilder的执行时间：" + (endTime - startTime));

        startTime = System.currentTimeMillis();
        for (int i = 0; i < 20000; i++) {
            text = text + i;
        }
        endTime = System.currentTimeMillis();
        System.out.println("String的执行时间：" + (endTime - startTime));

    }
}

package doy4;


import org.junit.Test;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;


public class DateTimeTest {

    //1.System类中的currentTimeMillis()
    @Test
    public void test1(){
        long time = System.currentTimeMillis();
        //返回当前时间与1970年1月1日0时0分0秒之间以毫秒为单位的时间差。
        //称为时间戳
        System.out.println(time);
    }
    
    @Test
    public void testSimpleDateFormat() throws ParseException, ParseException {
        //实例化SimpleDateFormat
        // SimpleDateFormat() ：默认的模式和语言环境创建对象
        SimpleDateFormat sdf = new SimpleDateFormat();

        //格式化：日期---》字符串
        Date date = new Date();
        System.out.println(date);   //Sun May 10 16:34:30 CST 2020

        String format = sdf.format(date);
        // public String format(Date date)：方法格式化时间对象date
        System.out.println(format); //20-5-10 下午4:34

        //解析：格式化的逆过程，字符串---》日期
        String str = "19-12-18 上午11:43";
        Date date1 = sdf.parse(str);
       //public Date parse(String source)：从给定字符串的开始解析文本，以生成 一个日期。
        System.out.println(date1);  //Wed Dec 18 11:43:00 CST 2019

        /

    @Test
    public void test2(){
        //构造器一：Date()：创建一个对应当前时间的Date对象
        Date date1 = new Date();
        System.out.println(date1.toString());   //Tue Oct 09 20:09:11 CST 2020
       //ublic String toString():返回该对象的字符串表示
        System.out.println(date1.getTime());    //1589026216998
        //getTime表示返回的毫秒数
        //构造器二：创建指定毫秒数的Date对象
        Date date2 = new Date(1589026216998L);
        //Date(long date)  里面需要传输long型数据，且后面带L
        System.out.println(date2.toString());

        //创建java.sql.Date对象
        java.sql.Date date3 = new java.sql.Date(35235325345L);
        System.out.println(date3);  //1971-02-13

        //如何将java.util.Date对象转换为java.sql.Date对象
        //情况一：
        Date date4 = new java.sql.Date(2343243242323L);
        java.sql.Date date5 = (java.sql.Date) date4;
        //情况二：
//        Date date6 = new Date();
//        java.sql.Date date7 = new java.sql.Date(date6.getTime());
    }
    @Test
    public void testExer() throws ParseException {
        String birth = "2020-09-08";

        SimpleDateFormat sdf1 = new SimpleDateFormat("yyyy-MM-dd");
        //yyyy代表的是4个位数的年数，MM表示精确到两位数的月份，dd表示精确到两位数的日数
        Date date = sdf1.parse(birth);
//        System.out.println(date);

        java.sql.Date birthDate = new java.sql.Date(date.getTime());
        System.out.println(birthDate);
    }

}

package doy4;


import java.util.Calendar;
import java.util.Date;

import org.junit.Test;


public class DateTime1 {

    
    //DAY_OF_MONTH--->日期    DAY_OF_YEAR---->这一年的第几天
    @Test
    public void testCalendar(){
        //1.实例化
        //方式一：创建其子类（GregorianCalendar）的对象
        //方式二：调用其静态方法getInstance()
        Calendar calendar = Calendar.getInstance();
//这个对象并不是Calendar 自身实例，而是其子类实例，这是在getInstance方法内部其实是实例化了GregorianCalendar 对象并返回了。
//        System.out.println(calendar.getClass());    //class java.util.GregorianCalendar

        //2.常用方法
        //get()获取
        int days = calendar.get(Calendar.DAY_OF_MONTH);//获取日期
        System.out.println(days);   //10
        System.out.println(calendar.get(Calendar.DAY_OF_YEAR)); //获取这一年的第几天//131,今天是这一年的131天

        //set()设置
        //calendar可变性
        calendar.set(Calendar.DAY_OF_MONTH,22);//修改日期
        days = calendar.get(Calendar.DAY_OF_MONTH);
        System.out.println(days);   //22

        //add()修改
        calendar.add(Calendar.DAY_OF_MONTH,-3);
        days = calendar.get(Calendar.DAY_OF_MONTH);
        System.out.println(days);   //22-3 --》19

        //getTime():日历类---> Date
        Date date = calendar.getTime();//返回当前时间到 自 1970 年 1 月 1 日 00:00:00 GMT 以来此 Date 对象表示的毫秒数。
        System.out.println(date);  //返回了一个Dare类型的 //Tue May 19 17:12:06 CST 2020

        //setTime():Date ---> 日历类
        Date date1 = new Date();
        calendar.setTime(date1);
        //public void setTime(long time)：设置此Date对象,以表示 1970 年1月1日 00:00:00 GMT以后 time 毫秒的时间点
        days = calendar.get(Calendar.DAY_OF_MONTH);
        System.out.println(days);   //10
    }
}

package doy4;


import org.junit.Test;

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;


public class DateTime {

    
    @Test
    public void testExer() throws ParseException {
        String birth = "2020-09-08";

        SimpleDateFormat sdf1 = new SimpleDateFormat("yyyy-MM-dd");
        Date date = sdf1.parse(birth);
//        System.out.println(date);

        java.sql.Date birthDate = new java.sql.Date(date.getTime());
        //new java.sql.Date(date.getTime())是什么意思
        //----->表示将java.util.Date下的date转化成毫秒数，传到java.sql.Date
        System.out.println(birthDate);
    }
    
    @Test
    public void testSimpleDateFormat() throws ParseException {
        //实例化SimpleDateFormat
        SimpleDateFormat sdf = new SimpleDateFormat();
// SimpleDateFormat() ：默认的模式和语言环境创建对象-->采用默认的时间格式
        //格式化：日期---》字符串
        Date date = new Date();//显示当前时间
        System.out.println(date);   //Sun May 10 16:34:30 CST 2020

        String format = sdf.format(date);
//        public String format(Date date)：方法格式化时间对象date 有返回值，Stirng类型的
        //格式化之后是'年份'-'月份'-'日期'  '上午或者下午''时间'
        System.out.println(format); //20-5-10 下午4:34

        //解析：格式化的逆过程，字符串---》日期
        String str = "19-12-18 上午11:43";
        Date date1 = sdf.parse(str);
        System.out.println(date1);  //Wed Dec 18 11:43:00 CST 2019
        
        /
public class JDK8DateTimeTest {

    @Test
    public void testDate(){
        //偏移量
        Date date1 = new Date(2020,9,8);
        System.out.println(date1);  //Fri Oct 08 00:00:00 CST 3920

        Date date2 = new Date(2020 - 1900,9 - 1,8);
        System.out.println(date2); //Tue Sep 08 00:00:00 CST 2020
    }
}

import org.junit.Test;

import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.LocalTime;


public class JDK8DateTimeTest {

    
    @Test
    public void test1(){
        //now():获取当前的日期、时间、日期+时间
        LocalDate localDate = LocalDate.now();
        LocalTime localTime = LocalTime.now();
        LocalDateTime localDateTime = LocalDateTime.now();

        System.out.println(localDate);
        System.out.println(localTime);
        System.out.println(localDateTime);

        //of():设置指定的年、月、日、时、分、秒。没有偏移量
        LocalDateTime localDateTime1 = LocalDateTime.of(2020, 10, 6, 13, 23, 43);
        System.out.println(localDateTime1);

        //getXxx()：获取相关的属性
        System.out.println(localDateTime.getDayOfMonth());
        System.out.println(localDateTime.getDayOfWeek());
        System.out.println(localDateTime.getMonth());
        System.out.println(localDateTime.getMonthValue());
        System.out.println(localDateTime.getMinute());

        //体现不可变性
        //withXxx():设置相关的属性
        LocalDate localDate1 = localDate.withDayOfMonth(22);
        System.out.println(localDate);
        System.out.println(localDate1);

        LocalDateTime localDateTime2 = localDateTime.withHour(4);
        System.out.println(localDateTime);
        System.out.println(localDateTime2);

        //不可变性
        LocalDateTime localDateTime3 = localDateTime.plusMonths(3);
        System.out.println(localDateTime);
        System.out.println(localDateTime3);

        LocalDateTime localDateTime4 = localDateTime.minusDays(6);
        System.out.println(localDateTime);
        System.out.println(localDateTime4);
    }
}

import org.junit.Test;

import java.time.*;


public class JDK8DateTimeTest {

    
    @Test
    public void test2(){
        //now():获取本初子午线对应的标准时间
        Instant instant = Instant.now();
        System.out.println(instant);    //2020-05-10T09:55:55.561Z

        //添加时间的偏移量
        OffsetDateTime offsetDateTime = instant.atOffset(ZoneOffset.ofHours(8));//东八区
        System.out.println(offsetDateTime); //2020-05-10T18:00:00.641+08:00

        //toEpochMilli():获取自1970年1月1日0时0分0秒（UTC）开始的毫秒数  ---> Date类的getTime()
        long milli = instant.toEpochMilli();
        System.out.println(milli);  //1589104867591

        //ofEpochMilli():通过给定的毫秒数，获取Instant实例  -->Date(long millis)
        Instant instant1 = Instant.ofEpochMilli(1550475314878L);
        System.out.println(instant1);   //2019-02-18T07:35:14.878Z
    }
}

import org.junit.Test;

import java.time.*;
import java.time.format.DateTimeFormatter;
import java.time.format.FormatStyle;
import java.time.temporal.TemporalAccessor;


public class JDK8DateTimeTest {

    
    @Test
    public void test3(){
        //方式一：预定义的标准格式。如：ISO_LOCAL_DATE_TIME;ISO_LOCAL_DATE;ISO_LOCAL_TIME
        DateTimeFormatter formatter = DateTimeFormatter.ISO_LOCAL_DATE_TIME;
        //格式化:日期-->字符串
        LocalDateTime localDateTime = LocalDateTime.now();
        String str1 = formatter.format(localDateTime);
        System.out.println(localDateTime);
        System.out.println(str1);//2020-05-10T18:26:40.234

        //解析：字符串 -->日期
        TemporalAccessor parse = formatter.parse("2020-05-10T18:26:40.234");
        System.out.println(parse);

        //方式二：
        //本地化相关的格式。如：ofLocalizedDateTime()
        //FormatStyle.LONG / FormatStyle.MEDIUM / FormatStyle.SHORT :适用于LocalDateTime
        DateTimeFormatter formatter1 = DateTimeFormatter.ofLocalizedDateTime(FormatStyle.LONG);
        //格式化
        String str2 = formatter1.format(localDateTime);
        System.out.println(str2);//2020年5月10日 下午06时26分40秒

        //本地化相关的格式。如：ofLocalizedDate()
        //FormatStyle.FULL / FormatStyle.LONG / FormatStyle.MEDIUM / FormatStyle.SHORT : 适用于LocalDate
        DateTimeFormatter formatter2 = DateTimeFormatter.ofLocalizedDate(FormatStyle.MEDIUM);
        //格式化
        String str3 = formatter2.format(LocalDate.now());
        System.out.println(str3);//2020-5-10


       //重点： 方式三：自定义的格式。如：ofPattern(“yyyy-MM-dd hh:mm:ss”)
        DateTimeFormatter formatter3 = DateTimeFormatter.ofPattern("yyyy-MM-dd hh:mm:ss");
        //格式化
        String str4 = formatter3.format(LocalDateTime.now());
        System.out.println(str4);//2020-05-10 06:26:40

        //解析
        TemporalAccessor accessor = formatter3.parse("2020-05-10 06:26:40");
        System.out.println(accessor);

    }
}

import org.junit.Test;

import java.time.*;
import java.util.Set;


public class JDK8DateTimeTest {
	
	@Test
	public void test1(){
		//ZoneId:类中包含了所有的时区信息
		// ZoneId的getAvailableZoneIds():获取所有的ZoneId
		Set zoneIds= ZoneId.getAvailableZoneIds();
		for(String s: zoneIds) {
			System.out.println(s);
		}
		// ZoneId的of():获取指定时区的时间
		LocalDateTime localDateTime= LocalDateTime.now(ZoneId.of("Asia/Tokyo"));
		System.out.println(localDateTime);
		
		//ZonedDateTime:带时区的日期时间
		// ZonedDateTime的now():获取本时区的ZonedDateTime对象
		ZonedDateTime zonedDateTime= ZonedDateTime.now();
		System.out.println(zonedDateTime);
		// ZonedDateTime的now(ZoneId id):获取指定时区的ZonedDateTime对象
		ZonedDateTime zonedDateTime1= ZonedDateTime.now(ZoneId.of("Asia/Tokyo"));
		System.out.println(zonedDateTime1);
	}
}

import java.time.Duration;
import java.time.LocalDateTime;
import java.time.LocalTime;

import org.junit.Test;

public class JDK8APITest {
	
	@Test
	public void test2(){
		//Duration:用于计算两个“时间”间隔，以秒和纳秒为基准
		LocalTime localTime= LocalTime.now();
		LocalTime localTime1= LocalTime.of(15, 23, 32);
		//between():静态方法，返回Duration对象，表示两个时间的间隔
		Duration duration= Duration.between(localTime1, localTime);
		System.out.println(duration);
		
		System.out.println(duration.getSeconds());
		System.out.println(duration.getNano());
		
		LocalDateTime localDateTime= LocalDateTime.of(2016, 6, 12, 15, 23, 32);
		LocalDateTime localDateTime1= LocalDateTime.of(2017, 6, 12, 15, 23, 32);
		
		Duration duration1= Duration.between(localDateTime1, localDateTime);
		System.out.println(duration1.toDays());
	}
}

import java.time.Period;
import org.junit.Test;

public class JDK8APITest {
	
	@Test
	public void test3(){
		//Period:用于计算两个“日期”间隔，以年、月、日衡量
		LocalDate localDate= LocalDate.now();
		LocalDate localDate1= LocalDate.of(2028, 3, 18);
		
		Period period= Period.between(localDate, localDate1);
		System.out.println(period);
        System.out.println(period.getYears());
		
		System.out.println(period.getMonths());
		System.out.println(period.getDays());
		
		Period period1= period.withYears(2);
		System.out.println(period1);
	}
}