The operator > is undefined for the argument type(s) void, void

Question

Hi, I get the error in title with this java code

public static void age(Ship ob){
    DateTime myBirthDate = ob.getDate();
    DateTime now = new DateTime();
    Period period = new Period(myBirthDate, now);

    System.out.print("Ship age is " + ob.getName() + " е " );

    PeriodFormatter formatter = new PeriodFormatterBuilder()
        .appendYears().appendSuffix(" years") 
        .appendMonths().appendSuffix(" months") 
        .appendWeeks().appendSuffix(" weeks") 
        .appendDays().appendSuffix(" days")
        .appendHours().appendSuffix(" hours")
        .appendMinutes().appendSuffix(" mnutes")       
        .appendSeconds().appendSuffix(" seconds\n ")
        .printZeroNever().toFormatter();

    String elapsed = formatter.print(period);
    System.out.println(elapsed);
}

public static void compare(Ship ob, Ship ob2) throws ParseException {
    if(age(ob2) > age(ob)){ //<---- I get the Error here , when i try to comapre two objects
        System.out.println( "The ship,wich is more years is " + ob2);
    } else
        System.out.println( "The ship,wich is more years is " + ob);
}

Can you help me? I tried many ways to fix this error but nothing helps, thanks.

Answer 1

Error is happening because you are trying to compare two void (s) using > operator in the following statement:

if(age(ob2) > age(ob))

your age method returns void as mentioned here:

public static void age(Ship ob)

You probably should return an integer value from age, which will make your comparison logical.

Answer 2

Your'e comparing two void return values. You should return an integer in age method, and probably change its logic.

Answer 3

int compareResult = ob.getDate().compareTo(ob2.getDate());
if (compareResult > 0) //ob2 date after ob date
    else if (compareResult < 0) //ob2 date before ob
        else //ob2 has same date as ob

Calculating age like this ain't good if you want to practice OOP. You should make an age method a member of Ship class. And/or have a comparison method in Ship class that accepts another Ship and returns result of date/age compare.