Calendar 类 set() 方法使用要点

相关源码：

/*
 * ...... 
 * 
Getting and Setting Calendar Field Values
 *
 * 
The calendar field values can be set by calling the set
 * methods. Any field values set in a Calendar will not be
 * interpreted until it needs to calculate its time value (milliseconds from
 * the Epoch) or values of the calendar fields. Calling the
 * get, getTimeInMillis, getTime,
 * add and roll involves such calculation.
 * ......
 */
public abstract class Calendar implements Serializable, Cloneable, Comparable {
    ......
}

• 可以通过set方法修改Calendar实例各个Field的值；
• 只有在真正需要使用calendar的值之前，这种改变才会生效；
• get()、getTimeMillis()、getTime()、add()、roll()方法可以触发set方法的修改。

例子：

public static void main(String[] args) {
        Calendar calendar = Calendar.getInstance();
        System.out.println(calendar);

        calendar.set(Calendar.DAY_OF_MONTH, 1);
        System.out.println(calendar);

        calendar.getTime();
        System.out.println(calendar);
}