Overloaded compareTo¶
ID: java/wrong-compareto-signature
Kind: problem
Security severity:
Severity: error
Precision: medium
Tags:
- reliability
- correctness
Query suites:
- java-security-and-quality.qls
Click to see the query in the CodeQL repository
Classes that implement Comparable<T> and define a compareTo method whose parameter type is not T overload the compareTo method instead of overriding it. This may not be intended.
Example¶
In the following example, the call to compareTo on line 17 calls the method defined in class Super, instead of the method defined in class Sub, because the type of a and b is Super. This may not be the method that the programmer intended.
public class CovariantCompareTo {
static class Super implements Comparable<Super> {
public int compareTo(Super rhs) {
return -1;
}
}
static class Sub extends Super {
public int compareTo(Sub rhs) { // Definition of compareTo uses a different parameter type
return 0;
}
}
public static void main(String[] args) {
Super a = new Sub();
Super b = new Sub();
System.out.println(a.compareTo(b));
}
}
Recommendation¶
To override the Comparable<T>.compareTo method, the parameter of compareTo must have type T.
In the example above, this means that the type of the parameter of Sub.compareTo should be changed to Super.
References¶
J. Bloch, Effective Java (second edition), Item 12. Addison-Wesley, 2008.
Java Language Specification: Overriding (by Instance Methods), Overloading.
The Java Tutorials: Overriding and Hiding Methods.