避免创建不必要的对象

一、错误做法

//不要这么做,每次isBabyBoomer被调用，都会新建一个Calendar和TimeZone两个实例
    public boolean isBabyBoomer(){
        Calendar gmtCal = Calendar.
                getInstance(TimeZone.getTimeZone("GMT"));
        gmtCal.set(1946,Calendar.JANUARY,1,0,0,0);
        Date boomStart = gmtCal.getTime();
        gmtCal.set(1965,Calendar.JANUARY,1,0,0,0);
        Date boomEnd = gmtCal.getTime();
        return birthDate.compareTo(boomStart) >= 0 &&
                birthDate.compareTo(boomEnd) < 0;
//    }

二、正确做法

    private final Date birthDate = null;

    private static  Date BOOM_START = null;
    private static  Date BOOM_END = null;
    static {
        Calendar gmtCal = Calendar.
                getInstance(TimeZone.getTimeZone("GMT"));
        gmtCal.set(1946,Calendar.JANUARY,1,0,0,0);
        BOOM_START = gmtCal.getTime();
        gmtCal.set(1965,Calendar.JANUARY,1,0,0,0);
        BOOM_END = gmtCal.getTime();
     }

    /**
     * 避免创建不必要的对象
     * @return
     */
     public boolean isBabyBoomer(){
         return birthDate.compareTo(BOOM_START) >= 0 &&
                 birthDate.compareTo(BOOM_END) < 0;
     }