JDK之Calendar

亦凉 2022-05-11 09:26 184阅读 0赞

## 功能 ##

*  时间处理工具类

> Calendar是一个抽象类，不能直接new一个实例，可以有两种方法得到它的实例
> 
>  *  方法一：Calendar cal = new GregorianCalendar();
>  *  方法二：Calendar cal = Calendar.getInstance();

## 用到的设计模式 ##

*  工厂模式

> java.util.Calendar\#getInstance()

public static Calendar getInstance()
    { 
        return createCalendar(TimeZone.getDefault(), Locale.getDefault(Locale.Category.FORMAT));
    }
    
    private static Calendar createCalendar(TimeZone zone,
                                           Locale aLocale)
    { 
        CalendarProvider provider =
            LocaleProviderAdapter.getAdapter(CalendarProvider.class, aLocale)
                                 .getCalendarProvider();
        if (provider != null) { 
            try { 
                return provider.getInstance(zone, aLocale);
            } catch (IllegalArgumentException iae) { 
                // fall back to the default instantiation
            }
        }
    
        Calendar cal = null;
    
        if (aLocale.hasExtensions()) { 
            String caltype = aLocale.getUnicodeLocaleType("ca");
            if (caltype != null) { 
               // 工厂模式的应用
                switch (caltype) { 
                case "buddhist":
                cal = new BuddhistCalendar(zone, aLocale);
                    break;
                case "japanese":
                    cal = new JapaneseImperialCalendar(zone, aLocale);
                    break;
                case "gregory":
                    cal = new GregorianCalendar(zone, aLocale);
                    break;
                }
            }
        }
        if (cal == null) { 
            // If no known calendar type is explicitly specified,
            // perform the traditional way to create a Calendar:
            // create a BuddhistCalendar for th_TH locale,
            // a JapaneseImperialCalendar for ja_JP_JP locale, or
            // a GregorianCalendar for any other locales.
            // NOTE: The language, country and variant strings are interned.
            if (aLocale.getLanguage() == "th" && aLocale.getCountry() == "TH") { 
                cal = new BuddhistCalendar(zone, aLocale);
            } else if (aLocale.getVariant() == "JP" && aLocale.getLanguage() == "ja"
                       && aLocale.getCountry() == "JP") { 
                cal = new JapaneseImperialCalendar(zone, aLocale);
            } else { 
                cal = new GregorianCalendar(zone, aLocale);
            }
        }
        return cal;
    }

## 应用 ##

*  设置时间

public static void main(String[] args) { 
         SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
         Calendar cl = Calendar.getInstance();
         System.out.println(sdf.format(cl.getTime()));
         System.out.println(cl.getTimeInMillis());
         System.out.println("------------------");
         cl.set(Calendar.HOUR_OF_DAY, 23);
         cl.set(Calendar.MINUTE, 59);
         cl.set(Calendar.SECOND, 59);
         System.out.println(sdf.format(cl.getTime()));
         System.out.println(cl.getTimeInMillis());
     }

*  时间处理

SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
    Calendar c = Calendar.getInstance();
    c.add(Calendar.DAY_OF_MONTH, -1);
    String end = dateFormat.format(c.getTime());
    map.put("end", end + " 23:59:59");
    c.add(Calendar.DAY_OF_MONTH, -defaultDays);
    String start = dateFormat.format(c.getTime());
    map.put("start", start + " 00:00:00");

## 源码 ##

### 成员属性 ###

public final static int ERA = 0;
    public final static int YEAR = 1;
    public final static int MONTH = 2;
    
    public final static int DAY_OF_WEEK = 7;
    public final static int SUNDAY = 1;
    public final static int MONDAY = 2;
    public final static int TUESDAY = 3;
    public final static int WEDNESDAY = 4;
    public final static int THURSDAY = 5;
    public final static int FRIDAY = 6;
    public final static int SATURDAY = 7;

### 构造函数 ###

protected Calendar()
     { 
         this(TimeZone.getDefaultRef(), Locale.getDefault(Locale.Category.FORMAT));
         sharedZone = true;
     }
     protected Calendar(TimeZone zone, Locale aLocale)
     { 
         fields = new int[FIELD_COUNT];
         isSet = new boolean[FIELD_COUNT];
         stamp = new int[FIELD_COUNT];
    
         this.zone = zone;
         setWeekCountData(aLocale);
     }

### 成员方法 ###

/** * Gets a calendar using the default time zone and locale. */
    public static Calendar getInstance()
     { 
         return createCalendar(TimeZone.getDefault(), Locale.getDefault(Locale.Category.FORMAT));
     }
     
     public static Calendar getInstance(TimeZone zone)
     { 
         return createCalendar(zone, Locale.getDefault(Locale.Category.FORMAT));
     }
     
     public final Date getTime() { 
         return new Date(getTimeInMillis());
     }
     
     public final void setTime(Date date) { 
         setTimeInMillis(date.getTime());
     }
     
     /** * Returns this Calendar's time value in milliseconds. */
     public long getTimeInMillis() { 
         if (!isTimeSet) { 
             updateTime();
         }
         return time;
     }
     
     public void setTimeInMillis(long millis) { 
         // If we don't need to recalculate the calendar field values,
         // do nothing.
         if (time == millis && isTimeSet && areFieldsSet && areAllFieldsSet
             && (zone instanceof ZoneInfo) && !((ZoneInfo)zone).isDirty()) { 
             return;
         }
         time = millis;
         isTimeSet = true;
         areFieldsSet = false;
         computeFields();
         areAllFieldsSet = areFieldsSet = true;
     }