Calculating Time and Date difference

I am currently writing a report to calculate the TotalTimeDifference between two date variables in iReport.

The two variables that I am comparing are MO_DATECREATED and MO_DATECOMPLETED and I am trying to calculate the time difference only.

I have tried setting up a variable that does a simple subtraction of the two variables- and of course that has not worked at all.

I will attach photoes of what I currently have but I am looking for the way to compare the two variables (which contains date/time) and printing out a variables with the difference in time.

Example: If the MO was started at 1/2/15 12:55pm and completed at 1/3/15 1:55pm i want to print the time difference, or how long it took, as 25 hours

How can I do this in iReport? Thank you for helping out a newbie!

EDIT After answer, I would like to the show days to:

You do not need variables for this, use directly the textFieldExpression

If the fields MO_DATECREATED and MO_DATECOMPLETED are declared:

as java.lang.Date

<field name="MO_DATECREATED" class="java.lang.Date">
    <fieldDescription><![CDATA[]]></fieldDescription>
</field>

The textFieldExpression would be ($F{MO_DATECOMPLETED}.getTime()-$F{MO_DATECREATED}.getTime())/(1000*60*60) + " hours".

Hey thats java exactly so to understand what it does check out this: How to calculate time difference in java?

as java.lang.String

<field name="MO_DATECREATED" class="java.lang.String">
    <fieldDescription><![CDATA[]]></fieldDescription>
</field>

We need to parse them to Date object's first.. your pattern is mm/dd/yy hh:mm a

(new java.text.SimpleDateFormat("mm/dd/yy hh:mm a").parse($F{MO_DATECOMPLETED}).getTime()-new java.text.SimpleDateFormat("mm/dd/yy hh:mm a").parse($F{MO_DATECREATED}).getTime())/(1000*60*60) + " hours"

Considering that they maybe null we better add a printWhenExpression as well

Complete result

<textField>
     <reportElement x="0" y="0" width="100" height="20" uuid="eac93a84-7901-4205-b09c-556d48dc05e1">
        <printWhenExpression><![CDATA[new java.lang.Boolean($F{MO_DATECREATED}!=null && $F{MO_DATECOMPLETED}!=null)]]></printWhenExpression>
    </reportElement>
    <textFieldExpression><![CDATA[(new java.text.SimpleDateFormat("mm/dd/yy hh:mm a").parse($F{MO_DATECOMPLETED}).getTime()-new java.text.SimpleDateFormat("mm/dd/yy hh:mm a").parse($F{MO_DATECREATED}).getTime())/(1000*60*60) + " hours"]]></textFieldExpression>
</textField>

No doubt that it is better that they are java.lang.Date object, both the report will fill faster, no risk for parsing error and you can export correctly to excel ecc. To format a java.lang.Date object as you wish just use the pattern property.

EDIT: Users has opted for the java.util.Date and asked how he can display also minutes, for this I have created a general question on How to create a single expression displaying time difference between two Date's as years, months, days, hours, minutes, seconds and it is now answered

This was the temporary solution

<textField>
     <reportElement x="0" y="0" width="100" height="20" uuid="eac93a84-7901-4205-b09c-556d48dc05e1">
        <printWhenExpression><![CDATA[new java.lang.Boolean($F{MO_DATECREATED}!=null && $F{MO_DATECOMPLETED}!=null)]]></printWhenExpression>
    </reportElement>
    <textFieldExpression><![CDATA[($F{MO_DATECOMPLETED}.getTime()-$F{MO_DATECREATED}.getTime()) / (24* 60 * 60 * 1000)  + " days " +($F{MO_DATECOMPLETED}.getTime()-$F{MO_DATECREATED}.getTime()) / (60 * 60 * 1000) % 24 + " hours " +  ($F{MO_DATECOMPLETED}.getTime()-$F{MO_DATECREATED}.getTime()) / (60 * 1000) % 60 + " minutes"]]></textFieldExpression>
</textField>