新手容易犯的日期错误

今天调试代码遇到一个新手容易犯的错误。demo如下

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


public class Test {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		Calendar c1 = Calendar.getInstance();
		Calendar c2 = Calendar.getInstance();
		SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
		
		try {
			long time_1 = sdf.parse("2012-01-01 00:00:00").getTime();
			long time_2 = sdf.parse("2012-03-01 00:00:00").getTime();
			c1.setTimeInMillis(time_1);
			c2.setTimeInMillis(time_2);
			System.out.println(c1.before(c2));	//result true
			System.out.println(c1.getTime().before(c2.getTime())); //result true
			System.out.println(c1.before(c2.getTime())); //result false
		} catch (ParseException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}

}

 在对日期类型使用before,after方法进行比较时要注意参数类型与对象类型的一致，否则结果为false