Why is this an issue?

Assuming that a comparator or compareTo method always returns -1 or 1 if the first operand is less than or greater than the second is incorrect.

The specifications for both methods, Comparator.compare and Comparable.compareTo, state that their return value is "a negative integer, zero, or a positive integer as this object is less than, equal to, or greater than the specified object." Even if a specific comparator always returns -1, 0, or 1, this is only an implementation detail, not the API contract developers can rely on.

How to fix it

Replace

Code examples

Noncompliant code example

public class Main {

  boolean isAGreaterThanB(Comparable<Integer> a, Integer b) {
    return a.compareTo(b) == 1; // Noncompliant, check for constant return value
  }

  public static void main(String[] args) {
    ByteComparator comparator = new ByteComparator();
    if (comparator.compare((byte) 23, (byte) 42) == -1) { // Noncompliant, check for constant return value
      System.out.println("23 < 42");
    } else {
      System.out.println("23 >= 42");
    }
  }

  static class ByteComparator implements Comparator<Byte> {
    @Override
    public int compare(Byte a, Byte b) {
      return a - b;
    }
  }
}

Compliant solution

public class Main {

  boolean isAGreaterThanB(Comparable<Integer> a, Integer b) {
    return a.compareTo(b) > 0; // Compliant, check for positive return value
  }

  public static void main(String[] args) {
    ByteComparator comparator = new ByteComparator();
    if (comparator.compare((byte) 23, (byte) 42) < 0) { // Compliant, check for negative return value
      System.out.println("23 < 42");
    } else {
      System.out.println("23 >= 42");
    }
  }

  static class ByteComparator implements Comparator<Byte> {
    @Override
    public int compare(Byte a, Byte b) {
      return a - b;
    }
  }
}

Resources

Documentation