Im trying to save two dates into a serialized . bin file. I use the Calendar class to get the current date then I add 30 days onto it. So I try to save two date variables fd (First Date) and ed (Expiration Date). If I change them to Strings in the expiration_date_serial file they work, but when I try to save them as Date they throw errors on these 2 lines:

我试图将两个日期保存为序列化。 bin文件。我使用Calendar类来获取当前日期,然后我将其添加30天。所以我尝试保存两个日期变量fd(First Date)和ed(Expiration Date)。如果我将它们更改为expiration_date_serial文件中的字符串,它们可以工作,但是当我尝试将它们保存为Date时,它们会在这两行上抛出错误:

exp_date.fd = current_formateddate;

exp_date.fd = current_formateddate;

exp_date.ed = formateddate;

exp_date.ed = formateddate;

Error: incompatible types: java.lang.String cannot be converted to java.util.Date

错误:不兼容的类型:java.lang.String无法转换为java.util.Date

Runnable Class:

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

public class GetCurrentDate {
public static void main(String[] args) {
    // get current date
    DateFormat currentdateFormat = new SimpleDateFormat("MM/dd/yy");

    Date current_date = new Date();

    String current_formateddate = currentdateFormat.format(current_date);
    System.out.println("Current date:  " + (current_formateddate));

    // ADD 30 days to the current date
    DateFormat dateFormat = new SimpleDateFormat("MM/dd/yy");
    Calendar c = Calendar.getInstance();
    c.add(Calendar.DATE, 30);
    Date d = c.getTime();
    String formateddate = dateFormat.format(d);

    System.out.println("+ 30 days: " + formateddate);


    // Serialization start
    expiration_date_serial exp_date = new expiration_date_serial();
    exp_date.fd = current_formateddate;
    exp_date.ed = formateddate;

    String fileName = "data.bin";
    try {
        ObjectOutputStream os = new ObjectOutputStream(
                new FileOutputStream(fileName));
        os.writeObject(exp_date);
        os.close();
    } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    System.out.println("Done writing...");

    try {
        ObjectInputStream is = new ObjectInputStream(new FileInputStream(
                fileName));
        expiration_date_serial p = (expiration_date_serial) is.readObject();
        System.out.println("First Date = " + p.fd +
                " Expiration Date = " + p.ed);
    } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    } catch (ClassNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}

}

Other class:

import java.io.Serializable;
import java.util.Date;


public class expiration_date_serial implements Serializable {
public Date fd;//First Date
public Date ed;//Expiration Date
}

2 个解决方案

#1

tl;dr

LocalDate.now( ZoneId.of( "America/Montreal" ) )
         .plusDays( 30 )
         .toString()

Details

The Answer by Orlangure is correct, about assigning across types.

Orlangure的回答是正确的,关于跨类型的分配。

Also, other problems include:

此外,其他问题包括:

Using old outmoded legacy classes for date-time handling.

使用旧的过时遗留类进行日期时间处理。

Poor choice of format for serialized date values.

序列化日期值的格式选择不佳。

Incorrectly choosing to use a date-time class for a date-only value.

错误地选择将日期时间类用于仅日期值。

java.time

The old date-time classes are poorly-designed, confusing, and troublesome. Avoid them. Now legacy, supplanted by the java.time classes.

旧的日期时间类设计糟糕,令人困惑,麻烦。避免他们。现在遗留下来,取而代之的是java.time类。

ISO 8601

The ISO 8601 standard defines textual formats for date-time values. These formats are unambiguous, intuitive across cultures, and practical. The standard format for a date-only value is YYYY-MM-DD such as 2016-10-23.

ISO 8601标准定义了日期时间值的文本格式。这些格式在各种文化中都是明确的,直观的,实用的。仅日期值的标准格式为YYYY-MM-DD,例如2016-10-23。

The java.time classes use ISO 8601 by default when parsing and generating Strings to represent their date-time values.

在解析和生成字符串以表示其日期时间值时,java.time类在默认情况下使用ISO 8601。

`LocalDate`

The LocalDate class represents a date-only value without time-of-day and without time zone.

LocalDate类表示没有时间且没有时区的仅日期值。

A time zone is crucial in determining a date. For any given moment, the date varies around the globe by zone. For example, a few minutes after midnight in Paris France is a new day while still “yesterday” in Montréal Québec.

时区对于确定日期至关重要。对于任何给定的时刻,日期在全球范围内因地区而异。例如,法国巴黎午夜过后几分钟,在魁北克蒙特利尔的“昨天”仍然是新的一天。

ZoneId z = ZoneId.of( "America/Montreal" );
LocalDate today = LocalDate.now( z );

Strings

To generate an ISO 8601 compliant String, simply call toString.

要生成符合ISO 8601标准的String,只需调用toString即可。

String output = today.toString();  // 2016-10-23

To parse, simply call parse.

要解析,只需调用解析。

LocalDate ld = LocalDate.parse( "2016-10-23" );

Date math

You can add or subtract amounts of time. Just call the plus… and minus… methods.

您可以添加或减去一定的时间。只需调用plus ...和minus ...方法。

LocalDate thirtyDaysAgo = ld.minusDays( 30 );
LocalDate oneMonthAgo = ld.minusMonths( 1 );

About java.time

The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date, Calendar, & SimpleDateFormat.

java.time框架内置于Java 8及更高版本中。这些类取代了麻烦的旧遗留日期时间类,如java.util.Date,Calendar和SimpleDateFormat。

The Joda-Time project, now in maintenance mode, advises migration to java.time.

现在处于维护模式的Joda-Time项目建议迁移到java.time。

To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations. Specification is JSR 310.

要了解更多信息,请参阅Oracle教程。并搜索Stack Overflow以获取许多示例和解释。规范是JSR 310。

Where to obtain the java.time classes?

从哪里获取java.time类?

Java SE 8 and SE 9 and later
- Built-in.
- Part of the standard Java API with a bundled implementation.
- Java 9 adds some minor features and fixes.

Java SE 8和SE 9及更高版本内置。带有捆绑实现的标准Java API的一部分。 Java 9增加了一些小功能和修复。

Java SE 6 and SE 7
- Much of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.

Java SE 6和SE 7大部分java.time功能都被反向移植到ThreeTen-Backport中的Java 6和7。

Android
- The ThreeTenABP project adapts ThreeTen-Backport (mentioned above) for Android specifically.
- See How to use….

Android ThreeTenABP项目专门针对Android调整ThreeTen-Backport(如上所述)。请参阅如何使用....

The ThreeTen-Extra project extends java.time with additional classes. This project is a proving ground for possible future additions to java.time. You may find some useful classes here such as Interval, YearWeek, YearQuarter, and more.

ThreeTen-Extra项目使用其他类扩展了java.time。该项目是未来可能添加到java.time的试验场。您可以在这里找到一些有用的课程,如Interval,YearWeek,YearQuarter等。

将日期保存到序列化文件