Compare operators custom object java

Question

Is there a plug in that supports compare operations on a custom object?

I would like to use this:

class MyTemperatureObject implements Comparable<MyTemperatureObject> {
    ...
    @Override
    public int compareTo(MyTemperatureObject object) {
       return getValue().compareTo(object.getValue());
    }
}

MyTemperatureObject a;
MyTemperatureObject b;

if (a < b){
    ...
}

This gives the compile error:

Operator '<' cannot be applied to MyTemperatureObject

But I think that the compiler can use the Comparable interface to evaluate this. Or is there maybe a reason that this is not possible or not wisely to do this.

I know that I can use the compareTo function

a.compareTo(b) < 0

But I think this is better readable/understandable

 a < b

I think this is better readable/understandable a<b, is not supported in Java for MyTemperatureObject. — Naman Gala
– Naman Gala, Commented Apr 20, 2015 at 7:24
And in future if you get another doubt of using equals method instead of == as it is more readable/understandable, then please refer this answer. — Naman Gala
– Naman Gala, Commented Apr 20, 2015 at 7:28

Robby Cornelissen · Accepted Answer · 2015-04-20 07:17:14Z

5

In Java, the < operator can only be used on numeric types. The compiler will not automagically apply the compareTo method for object comparisons.

Rewrite your condition as follows:

if (a.compareTo(b) < 0){ /* ... */ }

The semantics of the compareTo method are clearly documented in the JavaDoc, but in essence it boils down to this:

Returns a negative integer, zero, or a positive integer as this object is less than, equal to, or greater than the specified object.

edited Apr 20, 2015 at 7:17

answered Apr 20, 2015 at 7:11

Robby Cornelissen

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4 Comments

Dragos Rizescu Over a year ago

I think you should explain him the return value of the compareTo method as well.

bmooij Over a year ago

I know this function I have implemented this function. But what I want is to not use this function. a < b is more understandable than a.compareTo(b) < 0

bmooij Over a year ago

But what are the downsides for to not support this?

Robby Cornelissen Over a year ago

I don't see any immediate downsides. Dealing with null cases would probably be a little bit tricky, as well as dealing with incompatible types. All issues that could probably be solved more or less elegantly, but I can't speculate about the original language designers' motivations.

Vyncent · Accepted Answer · 2015-04-20 07:14:33Z

2

if you want to do like on C++ operator overloading : Wikipedia - C++ Operator Overloading, then it doesn't exist on java.

answered Apr 20, 2015 at 7:14

Vyncent

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Comments

Naman Gala · Accepted Answer · 2015-04-20 07:21:30Z

0

You can refer documentation of compareTo method.

Returns: a negative integer, zero, or a positive integer as this object is less than, equal to, or greater than the specified object.

You can use compareTo method.

if (a.compareTo(b) < 0){
    // Your code
}

Operator '<' cannot be applied to MyTemperatureObject

Answer : Operator overloading is not supported in Java, as it is supported in C++. So you can use < / > operator for numeric comparison only.

edited Apr 20, 2015 at 7:21

answered Apr 20, 2015 at 7:15

Naman Gala

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Comments

AKZ · Accepted Answer · 2015-04-20 07:22:46Z

0

You must use specific class that invoke compareTo method, Take a look as this tutorial, I hope help you http://www.tutorialspoint.com/java/java_using_comparator.htm

answered Apr 20, 2015 at 7:22

AKZ

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