packagemeta;publicclassBirthDate{privateintday=1;privateintmonth=1;privateintyear=1900;publicBirthDate(intday,intmonth,intyear){this.day=day;this.month=month;this.year=year;}publicBirthDate(BirthDatedate){this.day=date.day;this.month=date.month;this.year=date.year;}publicBirthDateaddDays(intadd_days){BirthDatedate1=newBirthDate(this);//構(gòu)造方法用this作為參數(shù)調(diào)用date1.day=date1.day+add_days;returndate1;}publicstaticBirthDateaddDays2(BirthDatedate1,intadd_days){date1.day=date1.day+add_days;returndate1;}publicstaticvoidprintDate(BirthDatedate){System.out.println(date.year+""+date.month+""+date.day);}publicstaticvoidmain(String[]args){//TODOAuto-generatedmethodstubBirthDatedate0=newBirthDate(3,5,1988);printDate(date0);date0=date0.addDays(7);printDate(date0);date0=addDays2(date0,4);printDate(date0);}}第一，構(gòu)造方法publicBirthDate(BirthDatedate)這種調(diào)用自身類類型作為參數(shù)究竟是什么意思？目的何在？第二，BirthDatedate1=newBirthDate(this);這里的this又作為了參數(shù)目的是什么？