Converting 24 hour clock to 12 hour java

Question

Okay so I have a clock class which is initially set as a 24 hour clock but I have to have the clock display as a 12 hour clock using only this method! I have tried for hours but have fallen short! Please help. Make the clock display the time as a 12 hour clock (hh:mm:ss AM/PM). Use abstraction - don’t change anything but the updateDisplay() method. The clock can use military time "under the covers"; it just needs to return the proper string when getTime() is called.

private void updateDisplay()
{
    String AM = "AM";
    String PM = "PM";

    if(hours.getValue() == 0) {
        hours.setValue(hours.getValue() + 12);
        PM = "";
    }
    else if(hours.getValue() == 1 < hours.getValue() && hours.getValue() < 11) {
        PM = "";
    }
    else if(hours.getValue() == 12) {
       AM = "";
    }
    else if(hours.getValue() == 13 > 24) {
        hours.setValue(hours.getValue() - 12);
       AM = "";
    }

    displayString = hours.getDisplayValue() + ":" + 
    minutes.getDisplayValue() + ":" +
    seconds.getDisplayValue() + PM + AM;
}

Tim · Accepted Answer · 2013-01-28T05:25:22.607

A 24 Hour clock, H, runs from 0<=H<=23. If H div 12 is 0, then AM, else PM. Then the 12 Hour clock, h, is H mod 12 unless that value is 0, in which case h = 12. You shouldn't be changing the value (hours.setValue(...)) in your display code, nor do you need to convert to seconds. I think the issue with your code is just a syntax problem in the first conditional statement.

... if(hours.getValue() == 1 < hours.getValue() ... // This is wrong

You are comparing the value of hours to 1, and then the result of the comparison to hours. This won't compile in java, because bools are incomparable to ints.

Note: When I say div, I mean an integer division (i.e. truncated / operator in Java), and when I say mod I mean an integer modulus (% operator in Java).

Update: All you need to do is convert your 24 hour value hours.getValue() to the 12 Hour equivalent for display. Something along the lines of:

// Not correct Java!
string meridianNess = (hours.getValue()/12==0?"AM":"PM");
int h = hours.getValue()%12;
if (h==0) h = 12;
System.out.print(h+":"+new NumberFormat("00").format(minutes.getValue())+":"+
    new NumberFormat("00").format(seconds.getValue())+" "+meridianNess);

So.... all I need to do is code A 24 Hour clock, H, runs from 0<=H<=23. If H div 12 is 0, then AM, else PM. Then the 12 Hour clock, h, is H mod 12 unless that value is 0, in which case h = 12. And that will turn my 24 hour clock to 12 hour? — DrJonesYu, Jan 28 '13 at 05:13
Thanks I got it to work and I understand most of it but can you explain what (hours.getValue()/12==0?"AM":"PM") does? Thank you! — DrJonesYu, Jan 28 '13 at 16:46
It's called a ternary operator, and is basically just a condensed if/else statement. You can read that as "IF hours dot get value divided by 12 EQUALS 0 THEN return am ELSE return PM". Whichever one gets returned will be assigned to meridianNess. Also, I'm glad it worked for you, would you mind accepting my answer? Thanks. — Tim, Jan 28 '13 at 18:54

score 1 · Answer 2 · answered Mar 11 '15 at 08:29

A nice concise formula for this that works well is to add 11, then take the 'modulo 12', and then add one more:

hours.setValue(((hours.getValue()+11)%12)+1);

i.e.

h_12 = ( (h_24+11) % 12 ) + 1

This works out to give the desired result for any value including hours=0, hours=12, etc.

(And then of course use any of the solutions mentioned previously for the AM/PM display)

score 0 · Answer 3 · answered Jan 28 '13 at 03:20

0

Try converting the 24h time to seconds, then it should be easy...

answered Jan 28 '13 at 03:20

Rui Brito

44
3

Converting 24 hour clock to 12 hour java

3 Answers3