The method getTime() is undefined for the type Obj

问题:

I have created an application that generates a difference between two dates when u click on a button named "calculate difference", but I don't know whats wrong with this code. I tried different methods and without any result. If you can help me I will be grateful guys.

public class DateForm extends javax.swing.JPanel {

    String date1 = "26/02/2011";
    String time1 = "11:00 AM";
    String date2 = "27/02/2011";
    String time2 = "12:15 AM";
    SimpleDateFormat sdf = new SimpleDateFormat("dd/MM/yyyy hh:mm a");
    private Object dateObj1;
    private Object dateObj2;

    public DateForm() {
        initComponents();
    }      

    private void btnActionPerformed(java.awt.event.ActionEvent evt) {                                    
        try {
            Date dateObj1 = sdf.parse(date1 + " " + time1);
        } catch (ParseException ex) {
            Logger.getLogger(DateForm.class.getName()).log(Level.SEVERE, null, ex);
        }
        try {
            Date dateObj2 = sdf.parse(date2 + " " + time2);        // TODO add your handling code here:
        } catch (ParseException ex) {
            Logger.getLogger(DateForm.class.getName()).log(Level.SEVERE, null, ex);
        }
        System.out.println(dateObj1);
        System.out.println(dateObj2);
        long diff = dateObj2.getTime() - dateObj1.getTime();
        double diffInHours = diff / ((double) 1000 * 60 * 60);
        System.out.println(diffInHours);
        System.out.println("Hours " + (int)diffInHours);
        System.out.println("Minutes " + (diffInHours - (int)diffInHours)*60 );

    } 
}

回答1:

Since it's 2018, you really should be making use of the date/time APIs introduced in Java 8 (or the ThreeTen Backport if you're Java 7 or below)

String date1 = "26/02/2011";
String time1 = "11:00 AM";
String date2 = "27/02/2011";
String time2 = "12:15 AM";

DateTimeFormatter formatter = DateTimeFormatter.ofPattern("dd/MM/yyyy hh:mm a");

LocalDateTime start = LocalDateTime.parse(date1 + " " + time1, formatter);
LocalDateTime end = LocalDateTime.parse(date2 + " " + time2, formatter);

Duration duration = Duration.between(start, end);

long hours = duration.toHours();
long mins = duration.minusHours(hours).toMinutes();
// Or if you're using Java 9+
//long mins = duration.toMinutesPart();
System.out.println("Hours = " + hours);
System.out.println("Mins = " + mins);

which ouputs

Hours = 13
Mins = 15

I would recommend having a read of Date and Time Classes

"whats wrong with this code please?"

The following...

try {
    Date dateObj1 = sdf.parse(date1 + " " + time1);
} catch (ParseException ex) {
    Logger.getLogger(DateForm.class.getName()).log(Level.SEVERE, null, ex);
}
try {
    Date dateObj2 = sdf.parse(date2 + " " + time2);        // TODO add your handling code here:
} catch (ParseException ex) {
    Logger.getLogger(DateForm.class.getName()).log(Level.SEVERE, null, ex);
}

Is simply creating two objects whose scope is only relevant to the try-catch blocks they are defined in, dateObj1 and dateObj2 can't be accessed outside of those blocks ... but ...

You define...

private Object dateObj1;
private Object dateObj2;

as instance fields, which means...

System.out.println(dateObj1);
System.out.println(dateObj2);

will most likely print null and...

long diff = dateObj2.getTime() - dateObj1.getTime();

won't compile, because dateObj1 and dateObj2 are just defined as Object and Object doesn't have a getTime method

Date/time calculations are complex and governed by many different rules (further complicated by the type of calendar you are using)

Simply doing...

double diffInHours = diff / ((double) 1000 * 60 * 60);

is naive at best, broken at worst

And...

System.out.println("Minutes " + (diffInHours - (int)diffInHours)*60 );

is well, pointless, what's (something - something) * 60?

回答2:

MadProgrammer’s answer is a very good one. I’d just like to supply a detail: Depending on taste you may parse the date and time strings separately and combine them after parsing:

    DateTimeFormatter dateFormatter = DateTimeFormatter.ofPattern("dd/MM/uuuu");
    DateTimeFormatter timeFormatter 
            = DateTimeFormatter.ofPattern("hh:mm a", Locale.ENGLISH);

    String date1 = "26/02/2011";
    String time1 = "11:00 AM";
    LocalDateTime start = LocalDate.parse(date1, dateFormatter)
            .atTime(LocalTime.parse(time1, timeFormatter));
    System.out.println(start);

Output is:

2011-02-26T11:00

One potential advantage is in case of a bug in one of the parsed string you will get a preciser error message.

And one more detail now I’m at it: specify locale. AM and PM are called other things in other languages, so to make sure that your code works on other computers and also on the day when you play with your regional settings…