設計模式-Builder(建立者)

Builder 定義

1. 使用物件有多參數輸入時，可以簡化多參數建立並初始化實例功能
2. 強調物件屬性與物件建構可以分離，不同建構可以表示不同物件

Builder 使用情況

1. 初始化參數因參數多，簡化參數建立過程
2.

Builder 案例

這是利用Buildr模式來簡化日期計算可以看到DateBuilder建立只有基本參數宣告，實際計算方法是建立在Builder物件中，最後載執行由Calendar做日期加減的計算。建立者分離的物件參數與計算方法，但是帶來良好封裝性

    /**
     * Name: builder
     * Description :  日期建立可以自由輸入年 月 日後，建立日期
     * Created by blackbryant on 2017/1/7.
     */
    public class DateBuilder {
        private Locale locale ; 
        private String format ; 
        private int day ; 
        private int month ; 
        private int year ; 
        private int hour ;
        private int minute ; 
        private int second ;
        private String date ; 

        //需要宣告為靜態類別
        public static class Builder{
            private Locale locale ; 
            private String format ; 
            private int day ; 
            private int month ; 
            private int year ; 
            private int hour ;
            private int minute ; 
            private int second ;
            private String date ; 

            public Builder(String calDate, String formate){
                this.date = calDate ;
                this.format = formate ;
            }

            public DateBuilder build(){
                return new DateBuilder(this) ;
            }

            public Builder addDay(int day){
                this.day = day  ; 
                return this;
            }

            public Builder addMonth(int month){
                this.month = month  ; 
                return this;
            }

            public Builder addYear(int year){
                this.year = year  ; 
                return this;
            }

            public Builder addHour(int hour){
                this.hour = hour;
                return this;
            }

            public Builder addMinute(int minute){
                this.minute = minute ; 
                return this ;
            }

            public Builder addSecond(int second){
                this.second = second ;
                return this;
            }

            public Builder setformat(String format){
                this.format = format ; 
                return this ;
            }
        }

        private DateBuilder(Builder builder){
            this.locale = builder.locale ;
            this.year = builder.year ; 
            this.month = builder.month ; 
            this.day = builder.day ; 
            this.hour = builder.hour ; 
            this.minute = builder.minute ; 
            this.second = builder.second ; 
            this.format = builder.format ;
            this.date = builder.date ;
        }


        public Locale getLocale() {
            return locale;
        }

        public String getFormat() {
            return format;
        }

        public int getDay() {
            return day;
        }

        public int getMonth() {
            return month;
        }

        public int getYear() {
            return year;
        }

        public int getHour() {
            return hour;
        }

        public int getMinute() {
            return minute;
        }

        public int getSecond() {
            return second;
        }

        public String getDate(){
            return date ;
        }

        @Override
        public String toString() {
            StringBuilder sb = new StringBuilder() ; 
            sb.append("locale="+this.locale) ; 
            sb.append("year="+this.year) ; 
            sb.append("month="+this.month) ; 
            sb.append("day="+this.day) ; 
            sb.append("hour="+this.hour) ; 
            sb.append("minute="+this.minute) ; 
            sb.append("second="+this.second) ; 
            sb.append("format="+this.format) ; 
            return sb.toString();
        }

        public  static  void main(String[] args){
            DateBuilder dateBuilder = new DateBuilder.Builder("2001-01-01","yyyy-MM-dd").addDay(2).build() ;

            SimpleDateFormat sdf = new SimpleDateFormat(dateBuilder.getFormat()) ;

            try {
                Date calDate = sdf.parse(dateBuilder.getDate());
                Calendar c = Calendar.getInstance() ;
                c.setTime(calDate);
                c.add(Calendar.YEAR,  dateBuilder.getYear());
                c.add(Calendar.MONTH, dateBuilder.getMonth());
                c.add(Calendar.DAY_OF_MONTH, dateBuilder.getDay());
                c.add(Calendar.HOUR, dateBuilder.getHour());
                c.add(Calendar.MINUTE, dateBuilder.getMinute());
                c.add(Calendar.SECOND, dateBuilder.getSecond());
                Date afterDate = c.getTime() ;
                System.out.print("add 1 day : " +afterDate.toString());
            } catch (ParseException e) {
                e.printStackTrace();
            }
        }
    }