Java各种数据类型互转

一时失言乱红尘 2022-11-25 13:26 115阅读 0赞

> **目录**
> 
> 一、int转String
> 
> 二、String转int
> 
> 三、char转int
> 
> 四、String 转 double
> 
> 五、String 转 Float
> 
> 六、String为Long
> 
> 七、String与Date互转
> 
> 八、使用正则表达式判断String是否为int整型or浮点型数据
> 
> 九、判断字符串是否为数字
> 
> --------------------
> 
> ### 一、int转String ###
> 
>     public class IntegerDemo2 {
>     public static void main(String[] args) {
>     	int num=100;
>     	//1
>     	String s1=""+num;
>     	System.out.println(s1);
>     	//2
>     	String s2 =String.valueOf(num);
>     	System.out.println(s2);
>         //3
>         Integer i =new Integer(num);
>     	String s3 =i.toString();
>     	System.out.println(s3);
>     	//4
>     	String s4 =Integer.toString(i);
>     	System.out.println(s4);
>     }
>     }
> 
> ### 二、String转int ###
> 
>     String s="100";
>     	Integer ii =new Integer(s);
>     	int x=ii.intValue();
>     	System.out.println(x);
>     	int y = Integer.parseInt(s);
>     	System.out.println(y);
> 
> ### 三、char转int ###
> 
>     char ch = '9';
>     if (Character.isDigit(ch)){  // 判断是否是数字
>     	int num = Integer.parseInt(String.valueOf(ch));
>     	System.out.println(num);
>     }	
>     
>     
>     char ch = '9';
>     if (Character.isDigit(ch)){  // 判断是否是数字
>     	int num = (int)ch - (int)('0');
>     	System.out.println(num);
>     }
> 
> ### 四、String 转 double ###
> 
> ![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xpYnVzaTAwMQ_size_16_color_FFFFFF_t_70][]
> 
> ### 五、String 转 Float ###
> 
> ![20200809193206793.png][]
> 
> ### 六、String为Long ###
> 
> 注意，当String为Long数据类型时，即String长度超过int的长度时转换int数据类型时会出现错误的结果
> 
> ![20200809193224400.png][]
> 
> ### 七、String与Date互转 ###
> 
>     package com.god.genius.basic.jdk8.date;
>     
>     import org.junit.jupiter.api.Test;
>     
>     import java.time.*;
>     import java.time.format.DateTimeFormatter;
>     import java.time.temporal.ChronoUnit;
>     import java.util.Date;
>     
>     /**
>      * @author liSir
>      * @date 2020/5/13
>      * @desp jdk8日期各种用法及各种转换使用
>      */
>     public class DateDemo {
>         public static void main(String[] args) {
>             //1.时间日期
>             getDateTime();
>             //2.LocalDateTime与String互转
>             timeToString();
>             //3.Date与LocalDateTime互转
>             dateToLocalDateTime();
>             //4.时间运算
>             demo4();
>             //6.时间戳、瞬时点、Date、本地时间、转换
>             demo7();
>         }
>     
>         private static void demo4() {
>             LocalDateTime ldt = LocalDateTime.now();
>             //-----获取指定单位的值:2020
>             int year = ldt.getYear();
>             //-----MAY,5
>             Month month = ldt.getMonth();
>             int value = month.getValue();
>             //140
>             int dayOfYear = ldt.getDayOfYear();
>             //-----19
>             int dayOfMonth = ldt.getDayOfMonth();
>             //TUESDAY,2
>             DayOfWeek dayOfWeek = ldt.getDayOfWeek();
>             int weekValue = dayOfWeek.getValue();
>             //-----9
>             int hour = ldt.getHour();
>             //-----18
>             int minute = ldt.getMinute();
>             //-----59
>             int second = ldt.getSecond();
>     
>             //2020-06-03T17:59:00.123
>             //指定时间单位的值 2022-06-12T17:58:21.040
>             LocalDateTime localDateTime = ldt.withDayOfMonth(12).withYear(2022);
>             //在现有时间上做加法 2021-05-03T17:59:42.689
>             LocalDateTime localDateTime1 = ldt.plusYears(1).plusMonths(-1);
>     
>             // 在现有时间上做减法
>             LocalDateTime ldt2 = LocalDateTime.now().minus(-2, ChronoUnit.MONTHS).minusDays(3);
>     
>             // 获取一天的开始或结束
>             LocalDateTime ldtStart = LocalDateTime.of(LocalDate.now(), LocalTime.MIN);
>             LocalDateTime ldtEnd = LocalDateTime.of(LocalDate.now(), LocalTime.MAX);
>     
>             // 时间是否在指定时间之前
>             boolean isBefore = ldt.isBefore(ldt2);
>     
>             // 时间是否在指定时间之后
>             boolean isAfter = ldt.isAfter(ldt2);
>     
>             // 比较两个日期是否相等 重写的equals可以直接比较
>             boolean equality = ldt.equals(ldt2);
>     
>             // 比较是否是周期性日期，比如 生日 节假日 账单日 等
>             MonthDay holiday = MonthDay.of(5, 1); // 五一
>     
>             boolean xx = holiday.equals(MonthDay.from(LocalDateTime.now())); // 今天是否是五一
>     
>             System.out.println(0);
>     
>     
>         }
>     
>         /**
>          * 测试数据转换及封装工具的使用
>          */
>         @Test
>         public void convert() {
>             /*Date date = DateUtils.parseDate("2018-08-01 21:22:22", DateUtils.DATE_YMDHMS);
>             LocalDateTime localDateTime = DateUtils.dateConvertToLocalDateTime(date);
>             Long localDateTimeSecond = localDateTime.toEpochSecond(ZoneOffset.of("+8"));
>             Long dateSecond = date.toInstant().atOffset(ZoneOffset.of("+8")).toEpochSecond();
>             Assert.assertTrue(dateSecond.equals(localDateTimeSecond));*/
>         }
>     
>     
>         private static void demo7() {
>             LocalDateTime now = LocalDateTime.now();
>             //1.获取秒数,毫秒数
>             long l = now.toEpochSecond(ZoneOffset.of("+8"));
>             long l1 = now.toInstant(ZoneOffset.of("+8")).toEpochMilli();
>             System.out.println(l);
>             System.out.println(l1);
>         }
>     
>         private static void dateToLocalDateTime() {
>             Date date = new Date();
>             LocalDateTime localDateTime = dateToLocalDateTime(date);
>             System.out.println("localDateTime->" + localDateTime);
>             Date date2 = localDateTimeToDate(LocalDateTime.now());
>             System.out.println(date2);
>         }
>     
>         private static Date localDateTimeToDate(LocalDateTime now) {
>             return Date.from(now.toInstant(ZoneOffset.of("+8")));
>         }
>     
>         private static LocalDateTime dateToLocalDateTime(Date date) {
>             return date.toInstant().atOffset(ZoneOffset.of("+8")).toLocalDateTime();
>         }
>     
>     
>         private static void timeToString() {
>             LocalDateTime now = LocalDateTime.now();
>             //1.LocalDateTime与String互转
>             DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd");
>             DateTimeFormatter formatter2 = DateTimeFormatter.ofPattern("yyyyMMddHHmmssSSS");
>             String dateTime = now.format(formatter2);
>             System.out.println(dateTime);
>             //字符串转时间,字符串必须带时分秒
>             String dateTimeStr = "2020-07-28 14:11:15";
>             DateTimeFormatter df = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
>             LocalDateTime dateTime2 = LocalDateTime.parse(dateTimeStr, df);
>             System.out.println(dateTime2);
>         }
>     
>         private static void getDateTime() {
>             //本地时间 09:07:12.976
>             LocalTime lt = LocalTime.now();
>             //本地日期 2020-05-19
>             LocalDate ld = LocalDate.now();
>     
>             //本地日期时间 2020-05-19T09:08:07.727
>             LocalDateTime now = LocalDateTime.now();
>             //创建一个指定的时间 2012-02-12T12:12:12
>             LocalDateTime ldt = LocalDateTime.of(2012, 2, 12, 12, 12, 12);
>     
>             //日期时间转日期或时间 2012-02-12
>             LocalDate localDate = ldt.toLocalDate();
>             //09:18:59.746
>             LocalTime localTime = ldt.toLocalTime();
>         }
>     
>     }
> 
> ### 八、使用正则表达式判断String是否为int整型or浮点型数据。 ###
> 
> 动态选择方法转换数据
> 
> ![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xpYnVzaTAwMQ_size_16_color_FFFFFF_t_70 1][]
> 
> ### 九、判断字符串是否为数字 ###
> 
>     //方法一：用JAVA自带的函数
>     public static boolean isNumeric(String str){
>        for (int i = str.length();--i>=0;){  
>            if (!Character.isDigit(str.charAt(i))){
>                return false;
>            }
>        }
>        return true;
>     }
>     
>     
>     
>     /*方法二：推荐，速度最快
>       * 判断是否为整数 
>       * @param str 传入的字符串 
>       * @return 是整数返回true,否则返回false 
>     */
>     
>       public static boolean isInteger(String str) {  
>             Pattern pattern = Pattern.compile("^[-\\+]?[\\d]*$");  
>             return pattern.matcher(str).matches();  
>       }
>     
>     
>     //方法三：
>     public static boolean isNumeric(String str){
>         Pattern pattern = Pattern.compile("[0-9]*");
>         return pattern.matcher(str).matches();   
>     }
>     
>     
>     
>     //方法四：
>     public final static boolean isNumeric(String s) {
>         if (s != null && !"".equals(s.trim()))
>             return s.matches("^[0-9]*$");
>         else
>             return false;
>     }
>     
>     
>     
>     //方法五：用ascii码 
>     public static boolean isNumeric(String str){
>         for(int i=str.length();--i>=0;){
>             int chr=str.charAt(i);
>             if(chr<48 || chr>57)
>                 return false;
>         }
>        return true;
>     }
> 
>

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[20200809193206793.png]: /images/20221124/1200d011a7d1470f933196962ada0bb6.png
[20200809193224400.png]: /images/20221124/a01ee3079ec04cde84c2535498272661.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xpYnVzaTAwMQ_size_16_color_FFFFFF_t_70 1]: /images/20221124/5e36044795174a5a8909fcb282b499cb.png