【java】java.util.Calendar类学习

public abstract class Calendar implements Serializable, Cloneable{}
public static Calendar getInstance()
    {
//其实，这个方法内部也是return new GregorianCalendar(zone, aLocale);利用其具体的实现子类
        return createCalendar(TimeZone.getDefault(), Locale.getDefault());
    }


/**吗的，原来Calendar是如此的抽象，以至于我们必须要用到 GregorianCalendar（公历历法） */
public class GregorianCalendar extends Calendar{}

public static void main(String[] args) {
		Calendar c1 = Calendar.getInstance();
		System.out.println(c1.getTime());
		
		//年，月，日，时，分，秒
		Calendar c2 = new GregorianCalendar(2008,8,8,18,10,5);
		System.out.println(c2.getTime());
		
}

结果：
Mon Dec 13 11:03:59 CST 2010
Mon Sep 08 18:10:05 CST 2008

c2好像出错了，打印的是Sep 汗一个~~看源码吧

     
    public final static int JANUARY = 0;
    public final static int FEBRUARY = 1;
    public final static int MARCH = 2;
    public final static int APRIL = 3;
    public final static int MAY = 4;
    public final static int JUNE = 5;
    public final static int JULY = 6;
    public final static int AUGUST = 7;
    public final static int SEPTEMBER = 8;
    public final static int OCTOBER = 9;
    public final static int NOVEMBER = 10;
    public final static int DECEMBER = 11;
    public final static int UNDECIMBER = 12;

january是从0开始的，擦了。推荐如下方法，看起来更美观，有点像sql中的TYPE.VARCHAR

Calendar c3 = new GregorianCalendar(2008,Calendar.FEBRUARY,8,18,10,5);
System.out.println(c3.getTime());

Fri Feb 08 18:10:05 CST 2008

*
若想取第几个月，则用

Calendar c3 = new GregorianCalendar(2008,Calendar.FEBRUARY,8,18,10,5);
System.out.println(c1.get(Calendar.MONTH));

同理，上下午就是c1.get(Calendar.AM_PM);

还有一个比较实用的，与Date转化

public final Date getTime() {
        return new Date( getTimeInMillis() );
    }

补充一个add方法，就像oracle中的Add_months(d,n)一样的用法，n可正可负。
工作中写了一个简单的方法，取一个月的最后一天，思路就是下个月的第一天减去1即可。

java.util.Calendar c = new  GregorianCalendar(2010,10,01);
		c.add(Calendar.DATE, -1);
		System.out.println(c.get(Calendar.MONTH)+1);
		System.out.println(c.get(Calendar.DAY_OF_MONTH));
		System.out.println(c.get(Calendar.YEAR));
		String endDate = String.valueOf(c.get(Calendar.YEAR))+String.valueOf(c.get(Calendar.MONTH)+1)+String.valueOf(c.get(Calendar.DAY_OF_MONTH));
		System.out.println(endDate);

10
31
2010
20101031