Java学习第26天-StringBuffer类、Data类、Calendar类

StringBuffer类：

package GaoJiTexing.chapter2.StingClass.StringBuffer;

public class StringBufferTest {
    public static void main(String[] args) {
        StringBuffer strBuffer=new StringBuffer();
        System.out.println(strBuffer.length());

        //在末尾追加字符串
        strBuffer.append("java");
        System.out.println(strBuffer.length());
        System.out.println(strBuffer);

        strBuffer.append("你好");
        String str=strBuffer.toString();
        System.out.println(str);


        System.out.println("============");
        //在指定位置插入字符串
        strBuffer.insert(0,"html");
        System.out.println(strBuffer);


    }
}

Data类

package GaoJiTexing.chapter2;
import java.text.SimpleDateFormat;
import java.util.Date;

public class DataTest {
    public static void main(String[] args) {
        Date date=new Date();
        //System.out.println(date.toLocaleString());//过时方法
        //简单的日期转换方法
        SimpleDateFormat sdf=
                new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        //HH为24小时制，hh为12小时制

        String dateStr=sdf.format(date);
        System.out.println(dateStr);
    }
}

Calendar类

package GaoJiTexing.chapter2;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Date;

public class CalendarTest {
    public static void main(String[] args) {
        Calendar cal=Calendar.getInstance();//得到实例
        //System.out.println(cal.toString());
        int y=cal.get(Calendar.YEAR);//根据对应（年份）编号取数据
        int M=cal.get(Calendar.MONTH)+1;
        int D=cal.get(Calendar.DATE);
        int h=cal.get(Calendar.HOUR);
        int m=cal.get(Calendar.MINUTE);
        int s=cal.get(Calendar.SECOND);

        System.out.println(y+"-"+M+"-"+D+" "+h+":"+m+":"+s);

        //System.out.println("======");
        //修改年月日等
        // cal.set(Calendar.YEAR,2021);
        // int year=cal.get(Calendar.YEAR);
        // System.out.println("year:"+year);

        System.out.println("=======");
        Date date=cal.getTime();
        SimpleDateFormat sdf=new SimpleDateFormat("yyyy年MM月dd日");
        String dataStr=sdf.format(date);

        System.out.println(dataStr);
        //month从0开始，填数据时需要实际数据减1
        System.out.println("==========");
        int week=getWeekCount(2015,3,1);
        System.out.println("week:"+week);
    }

    //获取指定日期在指定年份中的周数
    public static int getWeekCount(int year,int month,int date){
        Calendar cal=Calendar.getInstance();
        cal.set(year, month, date);
        return cal.get(Calendar.WEEK_OF_YEAR);
    }
}