equals

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

Is there a method similar to equals() that expresses "not equal to"? An example of what I am trying to accomplish is below: if (secondaryPassword.equals(initialPassword)) { JOptionPane.showMessageDialog(null, "You've successfully completed the program."); } else { secondaryPassword = JOptionPane.showInputDialog(null, "Your passwords do not match. Please enter you password again."); } I am trying to find something that will not require me to use if ( a != c) . Just put a '!' in front of the boolean expression "Not equals" can be expressed with the "not" operator ! and the standard .equals . if

I am a bit puzzled about the behaviour of SortedSet, see following example: public class Blah { public double Value { get; private set; } public Blah(double value) { Value = value; } } public class BlahComparer : Comparer<Blah> { public override int Compare(Blah x, Blah y) { return Comparer<double>.Default.Compare(x.Value, y.Value); } } public static void main() { var blahs = new List<Blah> {new Blah(1), new Blah(2), new Blah(3), new Blah(2)} //contains all 4 entries var set = new HashSet<Blah>(blahs); //contains only Blah(1), Blah(2), Blah(3) var sortedset = new SortedSet<Blah>(blahs, new

I am using Java 7, and I have the following class below. I implemented equals and hashCode correctly, but the problem is that equals returns false in the main method below yet hashCode returns the same hash code for both objects. Can I get more sets of eyes to look at this class to see if I'm doing anything wrong here? UPDATE: I replaced the line on which I call the Objects.hash method with my own hash function: chamorro.hashCode() + english.hashCode() + notes.hashCode() . It returns a different hash code, which is what hashCode is supposed to do when two objects are different. Is the Objects

Based on various bad experiences my rule of thumb as a Java programmer is to only implement equals() and hashCode() on immutable objects, where two instances of the object really are interchangeable. Basically I want to avoid situations like the HashMap key problem in that link, or like the following: Get a thing with a certain identity. Modify it. Add it to a set. (later) Get another thing with the same identity. Modify it. Add it to the same set. Fail to notice that this add doesn't actually happen, since the set thinks the thing is already there. Do something with the things in the set.

If I have a object like: public class Person { public int id {get;set;} public string name {get;set;} } And I want the behavior: Person a = new Person(); Person b = new Person(); a == b; and that a == b returns true, do I have to override the Object.Equals() method? or is there some other way of doing it without overriding the Equals method? EDIT I want to compare data, as I want to know if a external method that I call returns a new object or a object with different data than a new object Abbas There are a couple of ways you can do this. By default Equals() and == check for reference equality