Calendar   set方法：

先看原始碼：

/**
 * Sets the values for the calendar fields <code>YEAR</code>,
 * <code>MONTH</code>, and <code>DAY_OF_MONTH</code>.
 * Previous values of other calendar fields are retained.  If this is not desired,
 * call {@link #clear()} first.
 *
 * @param 
 
year the value used to set the <code>YEAR</code> calendar field.
 * @param month the value used to set the <code>MONTH</code> calendar field.
 * Month value is 0-based. e.g., 0 for January.
 * @param date the value used to set the <code>DAY_OF_MONTH</code> calendar field.
 
 * @see #set(int,int)
 * @see #set(int,int,int,int,int)
 * @see #set(int,int,int,int,int,int)
 */
public final void set(int year, int month, int date)
{
    set(YEAR, year);
set(MONTH, month);
set(DATE, date);
}

問題來了，當呼叫set時（例如2016-08-31），date加1，month會不會改變。

先測試一下and方法：

Calendar cal = Calendar.getInstance
 
();
//設定時間2016-08-31
cal.set(2016,Calendar.AUGUST,31);
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
System.out.println(sdf.format(cal.getTime()));
//add 天數加1
cal.add(Calendar.DAY_OF_MONTH, 1);
System.out.println(sdf.format(cal.getTime()));
//set 設定天數
cal.set(Calendar.DAY_OF_MONTH, 1);
System.out.println(sdf.format(cal.getTime()));

再測試一下date+1：

Calendar cal = Calendar.getInstance();
//設定時間2016-08-31
cal.set(2016,Calendar.AUGUST,31);
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
System.out.println(sdf.format(cal.getTime()));
Calendar cal2 = Calendar.getInstance();
cal2.set(cal.get(Calendar.YEAR),cal.get(Calendar.MONTH),cal.get(Calendar.DAY_OF_MONTH)+1);
System.out.println(sdf.format(cal2.getTime()));
cal2.set(2016,Calendar.AUGUST,360);
System.out.println(sdf.format(cal2.getTime()));