Java – how does CompareTo work?

I know CompareTo returns negative or positive results related to one string and another, but why:

public class Test {
    public static void main(String[] args) {
        String y = "ab2";
        if(y.compareTo("ac3") == -1) {
            System.out.println("Test");
        }
    }
}

It's true

public class Test {
    public static void main(String[] args) {
        String y = "ab2";
        if(y.compareTo("ab3") == -1) {
            System.out.println("Test");
        }
    }
}

So is it?

Solution

Comparable. The total contract of CompareTo (o) is returned

>Positive integer if greater than another object. > If it is lower than another object, it is a negative integer If this is equal to another object, > 0

In your example, "AB2" CompareTo ("AC3") = = - 1 and "AB2" CompareTo ("AB3") = = - 1 only means that "AB2" is lower than "AC3" and "AB3" Using these examples alone, you can't get anything about "AC3" and "AB3"

This result is expected because B precedes C in the alphabet (so "AB2" < "AC3") and 2 precedes 3 (so "AB2" < "AB3"): Java sorts the string lexicographically