CODEWITHSUNDEEP
javaeclipse
reez
reez

Reputation: 3

Java compareTo() undefined operator

I'm trying to write code that compares the marks of two report cards but everytime I use an operator like > or < it says it's undefined for the argument type. Could someone tell me what I am doing wrong?

Edit (from comments): The type of marks and getMarks is double[].

 * @param other
 * @return 1 if the average mark of calling object is more than average of parameter object
 * -1 if the average mark of calling object is less than average of parameter object
 * 0 if the average mark of calling object and the average of parameter object are the same
 */
public int compareTo(ReportCard other) {

    if(this.marks > other.getMarks()) {
        return 1;
        } else if (this.marks < other.getMarks()) {
            return -1;
        } else {
            return 0;
        }
    } //to be completed

Upvotes: 0

Views: 130

Answers (2)

RealSkeptic
RealSkeptic

Reputation: 34618

The operators <, >, <= and >= are only available for primitive numeric types (double,int,char etc.).

The type double [] is not a primitive type. It's an array type (which is an object). You have to devise your own way of comparing an array and write a loop for it.

Consider: what will you do if the current report card has 3 marks, and the other report card has 5 marks? Suppose the first three marks are the same. Which report card should be considered the greater?

If they have the same number of marks, then your loop should be something like (pseudocode):

For each element marks[i] in the current report card marks
    if it is greater than the other report card's mark at the same position
        return 1;
    else if it is less than the other report card's mark at the same position
        return -1;
end of loop
Return zero (the two arrays were exactly the same)

You need to expand this to consider the case when the arrays are not of the same length.

Note that this gives most significance to the first mark. If all marks are equally important, you may want to do something else, like comparing the mark averages or sums.

To sum up: you were trying to compare non-primitive values using the comparison operators. The operators are not defined for objects and array types and you have to write your own implementation that does this correctly.

Upvotes: 0

Sean Patrick Floyd
Sean Patrick Floyd

Reputation: 298838

your code can be simplified to:

public int compareTo(ReportCard other) {
    return Double.compare(this.getMarks(), other.getMarks());
}

Or, if you want to create a Comparator<ReportCard> rather than implementing Comparable<ReportCard>, then you can do something like this:

Comparator<ReportCard> comparator = Comparator.comparingDouble(ReportCard::getMarks);

Upvotes: 3

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