常用工具类介绍

Date类太老了,很多方法过时了,这里不详细介绍了LocalDateTime类常用方法:1 获取当前日期import java.sql.SQLOutput; import java.time.LocalDateTime; public class Demo1 { public static void main(String[] args) { //获取当前日期 LocalDateTime now LocalDateTime.now(); System.out.println(now); } }结果:2026-05-07T08:14:30.0243012 获取当前年月日import java.time.LocalDate; import java.time.LocalDateTime; public class Demo1 { public static void main(String[] args) { //获取当前年月日 LocalDate today LocalDate.now(); System.out.println(today); } }结果:2026-05-073 创建指定的日期import java.time.LocalDate; import java.time.LocalDateTime; public class Demo1 { public static void main(String[] args) { //创建指定日期时间 LocalDateTime time LocalDateTime.of(2026,5,19,23,45); System.out.println(time); } }结果:2026-05-19T23:454 根据字符串创建日期import java.time.LocalDate; import java.time.LocalDateTime; import java.time.format.DateTimeFormatter; public class Demo1 { public static void main(String[] args) { //定义时间字符串 String str 2026-05-07 08:20:45; //创建格式化对象 DateTimeFormatter formatter DateTimeFormatter.ofPattern(yyyy-MM-dd HH:mm:ss); //字符串转日期 LocalDateTime time LocalDateTime.parse(str,formatter); System.out.println(time); } }结果:2026-05-07T08:20:455 获取具体详细信息import java.time.LocalDateTime; public class Demo1 { public static void main(String[] args) { LocalDateTime now LocalDateTime.now(); System.out.println(年: now.getYear()); System.out.println(月: now.getMonthValue()); System.out.println(日: now.getDayOfMonth()); System.out.println(时: now.getHour()); System.out.println(分: now.getMinute()); System.out.println(秒: now.getSecond()); } }结果:年: 2026月: 5日: 7时: 8分: 40秒: 36 日期运算import java.time.LocalDateTime; public class Demo1 { public static void main(String[] args) { LocalDateTime now LocalDateTime.now(); //加法 System.out.println(now.plusDays(3)); //减法 System.out.println(now.minusDays(1)); //加小时 System.out.println(now.plusHours(5)); } }结果:2026-05-10T09:05:59.9673592026-05-06T09:05:59.9673592026-05-07T14:05:59.9673597 根据当前时间获取指定时间import java.time.LocalDateTime; public class Demo1 { public static void main(String[] args) { LocalDateTime now LocalDateTime.now(); LocalDateTime newTime now.withYear(2030).withMonth(10).withDayOfMonth(1).withHour(8).withMinute(30); System.out.println(newTime); } }结果:2030-10-01T08:30:04.602279BigDecimal类常用的构造方法1 加减乘import java.math.BigDecimal; public class Demo1 { public static void main(String[] args) { BigDecimal a new BigDecimal(10.5); BigDecimal b new BigDecimal(2.5); //加法 System.out.println(a.add(b)); //减法 System.out.println(a.subtract(b)); //乘法 System.out.println(a.multiply(b)); //除法 System.out.println(a.divide(b)); } }结果:13.08.026.254.22 除法BigDecimal做除法时有些结果会出现无限小数无限小数解决方法·指定保留几位小数·指定舍入方式标准写法:import java.math.BigDecimal; import java.math.RoundingMode; public class Demo1 { public static void main(String[] args) { BigDecimal a new BigDecimal(10); BigDecimal b new BigDecimal(3); BigDecimal result a.divide(b,2, RoundingMode.HALF_UP); System.out.println(result); } }结果:3.33