What is the purpose of overriding toString(), and what's the difference between Object's default implementation and a well-designed custom one?

Object's default toString() returns a largely unhelpful string combining the class name and the object's hash code in hexadecimal (e.g., com.example.Point@7852e922), which is rarely useful for debugging or logging; a well-designed custom toString() returns a concise, human-readable summary of the object's meaningful state (typically the class name plus its key field values), dramatically improving the usefulness of debugger displays, log output, and exception messages that happen to include the object, without needing to manually inspect individual fields.

public class Point {
    private final int x, y;

    @Override
    public String toString() {
        return "Point{x=" + x + ", y=" + y + "}";
    }
}

System.out.println(new Point(3, 4));
// Default would print: Point@7852e922 (unhelpful)
// Custom prints: Point{x=3, y=4} (immediately useful for debugging)