接受变量 Date 和 final int 并计算天差 [重复]

Question

我有一个关于方法的赋值，以及 Date 类型的 2 个变量：

• _borrowedDate（也与 Date 方法有关）
• _returnDate（也是Date 类型）

我还有一个int MAX_DAYS = 30

我需要设置一个borrowdate，然后接受一个returndate，如果返回日期的天数大于30（MAX_DAYS），与借用日期相比，我应该输出真的。

public class Book {
    private String _title;
    private String _author;
    private int _yearPublished;
    private int _noOfPages;
    private boolean _borrowed;
    private String _studentName;
    private Date _borrowedDate;
    private Date _returnDate;
    final int MAX_DAYS = 30;
    final int FINE = 5;
    final int MIN_YEAR =1800;
    final int MAX_YEAR = 2018;
    final int DEFAULT_YEAR = 2000;
    int d1;
    int days;

    public Book( String title, String author, int yearPublished, int noOfPages)
    {
        if (yearPublished <MIN_YEAR || yearPublished >MAX_YEAR){
            _yearPublished = DEFAULT_YEAR;
            _title = title;
            _author = author;
            _noOfPages = noOfPages;}
        else{
            _title = title;
            _author = author;
            _yearPublished = yearPublished;
            _noOfPages = noOfPages;

        }
    }

    public Book ( Book other) {
        _title = other._title;
        _author = other._author;
        _yearPublished = other._yearPublished;
        _noOfPages = other._noOfPages;
        _borrowed = other._borrowed;
        _studentName = other._studentName;
        _borrowedDate = other._borrowedDate;
        _returnDate = other._returnDate;

    }

    public boolean equal(Book compare){
        return ((_title == compare._title)&&(_author==compare._author)&&(_yearPublished==compare._yearPublished)
            &&(_noOfPages==compare._noOfPages)&&(_borrowed==compare._borrowed)&&(_studentName==compare._studentName)
            &&(_borrowedDate==compare._borrowedDate)&&(_returnDate==compare._returnDate));
    }

    boolean olderBook(Book other){
        return other._yearPublished > _yearPublished;
    }

    public int getYear(){
        return _yearPublished;
    }

    public int getPages(){
        return _noOfPages;
    }

    public String getTitle(){
        return _title;
    }

    public String getAuthor(){
        return _author;
    }

    public boolean getBorrowed(){
        return _borrowed;
    }

    public String toString(){
        return "Title:"+_title+"Author:"+_author+ "Year:"+_yearPublished+","+_noOfPages+"pages";
    }

    private  int calculateDate(int day, int month,int year){
        if(month<3){
            year--;
            month += 12;
        }
        return  365*year+year/4-year/100+year/400+((month+1)*306)/10+(day-62);
    }

    public void borrowBook(String name, Date d){
        _studentName = name;
        _borrowedDate = new Date(d);
        _borrowed = true;
    }

    public boolean returnBook(Date d){
        _returnDate = new Date(d);
        _studentName = null;

        return (_returnDate.after(_borrowedDate));
    }

    public int howLongBorrowed(Date d){
        return 5;   
    }

    public void setYear(int n){
        if(n > MAX_YEAR || n<MIN_YEAR){
            _yearPublished = _yearPublished;
        }
        else
            _yearPublished = n;
    }

    public Date getBorrowedDate(){
        return _borrowedDate;   
    }

    public String getStudentName(){
        return _studentName;
    }

    public Date getReturnDate(){
        return _returnDate;
    }

    public void setTitle(String s){
        _title = s;
    }

    public void setAuthor(String s){
        _author = s;
    }

    public void setPages(int n){
        _noOfPages = n;
    }

    public boolean sameAuthor(Book other){
        return other._author.equals(_author);
    }
}

代码尚未完成，只是在这个特定的事情上遇到了麻烦。 我尝试了明显的>，但由于变量类型不同，它不起作用。

.after 有效，但我需要在 30 天后专门做，仅此而已。

Answer 1

如果您使用的是 Java 8 或更高版本，最好使用 LocalDate 而不是 java.util.Date：

LocalDate today = LocalDate.now();
LocalDate later = today.plusDays(30);

将LocalDate 对象与isBefore、isEqual 和isAfter 方法进行比较。

如果您使用的是早期版本，或者出于某种原因您只是更喜欢使用 Date，则需要一个 Calendar 实例来执行此操作：

Calendar cal = Calendar.getInstance();
cal.setTime(date);
cal.add(Calendar.DATE, 30);