日期处理

//获得某月第一天 最后一天   上个月第一天  最后一天   本周第一个周一package DateDemo;

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

public class Demo05 {

    public static void main(String[] args) {
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
        System.out.println(sdf.format(getTheFirstDayOfWeek(Calendar.getInstance())));
        System.out.println(sdf.format(getTheFirstDayOfMonth(Calendar.getInstance())));
        System.out.println(sdf.format(getTheLastOfMonth(Calendar.getInstance())));
        System.out.println(sdf.format(getTheLastDayofTheLastMonth(Calendar.getInstance())));
        System.out.println(sdf.format(getTheFirstDayofTheLastMonth(Calendar.getInstance())));

    }

    public static Date getTheFirstDayOfWeek(Calendar c) {
        int day_of_week = c.get(Calendar.DAY_OF_WEEK) - 1;//一周的第几天
        if (day_of_week == 0){
            day_of_week = 7;
        }
        c.add(Calendar.DATE, -day_of_week + 1);
        c.set(c.get(Calendar.YEAR), c.get(Calendar.MONTH), c.get(Calendar.DAY_OF_MONTH), 0, 0, 0);
        return c.getTime();
    }

    public static Date getTheFirstDayOfMonth(Calendar c){//月的第一天
        c.set(Calendar.DAY_OF_MONTH, c.getActualMinimum(Calendar.DAY_OF_MONTH));
        c.set(c.get(Calendar.YEAR), c.get(Calendar.MONTH), c.get(Calendar.DAY_OF_MONTH), 0, 0, 0);
        return c.getTime();
    }

    public static Date getTheLastOfMonth(Calendar c){//月的最后一天
        c.set(Calendar.DAY_OF_MONTH, c.getActualMaximum(Calendar.DAY_OF_MONTH));
        c.set(c.get(Calendar.YEAR), c.get(Calendar.MONTH), c.get(Calendar.DAY_OF_MONTH), 23, 59, 59);
        return c.getTime();
    }

    public static Date getTheLastDayofTheLastMonth(Calendar c){//上个月最后一天
        c.add(Calendar.MONTH, -1);
        return getTheLastOfMonth(c);
    }

    public static Date getTheFirstDayofTheLastMonth(Calendar c){//上个月最后一天
        c.add(Calendar.MONTH, -1);
        return getTheFirstDayOfMonth(c);
    }

}