JDK8之前Calendar日历类（抽象类）的使用

• 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();
System.out.println(calendar.getClass());//class java.util.GregorianCalendar

• 常用方法

//get()
int days = calendar.get(Calendar.DAY_OF_MONTH);
System.out.println(days);
System.out.println(calendar.get(Calendar.DAY_OF_YEAR));//29

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

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

最重要的日历类

//getTime():日历类---> Date
Date date = calendar.getTime();
System.out.println(date);//Sat Mar 19 10:23:52 CST 2022

//setTime():Date ---> 日历类
Date date1 = new Date();
calendar.setTime(date1);
days = calendar.get(Calendar.DAY_OF_MONTH);
System.out.println(days);//29