Implementing equals method using compareTo

Question

General question: When implementing an override of the default equals method in Java, what concerns should I have about simply utilizing an already implemented compareTo method vs writing independent logic into the equals method? I noticed someone mention in another question that foo.equals((String)null) returns false whereas String.compareTo((String)null) throws a NullPointerException. What makes these inconsistent results ideal functionality?

Sample equals method:

@Override
public boolean equals(Object obj) {
    if (obj != null && obj instanceof MyClass) {
        MyClass msg = (MyClass)obj;
        return this.compareTo(msg) == 0;
    }
    return false;
}

Edit: Quote from documentation on Comparable

The natural ordering for a class C is said to be consistent with equals if and only if e1.compareTo(e2) == 0 has the same boolean value as e1.equals(e2) for every e1 and e2 of class C. Note that null is not an instance of any class, and e.compareTo(null) should throw a NullPointerException even though e.equals(null) returns false

Edit:

After further review, I find it of note that the Comparable documentation also states the following:

The implementor must ensure sgn(x.compareTo(y)) == -sgn(y.compareTo(x)) for all x and y. (This implies that x.compareTo(y) must throw an exception iff y.compareTo(x) throws an exception.)

Ergo, since null.compareTo(x) obviously throws a NPE, x.compareTo(null) should throw a NPE as well. Whereas for equals, that is not necessarily the case. I am pretty big on the proper handling of NPEs, so I find this relatively significant.

Answer 1

compareTo may involve a lot more work than is necessary just to get an equality answer, which may end up being a performance issue, depending on your application usage.

Other than that, following DRY principles it would be a good idea to re-use the code as you have suggested.