compareto

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

I can use it to sort by emp id but I'm not sure if it is possible to compare strings. I get an error the operator is undefined for strings. public int compareTo(Emp i) { if (this.getName() == ((Emp ) i).getName()) return 0; else if ((this.getName()) > ((Emp ) i).getName()) return 1; else return -1; What you need to use is the compareTo() method of Strings. return this.getName().compareTo(i.getName()); That should do what you want. Usually when implementing the Comparable interface, you will just aggregate the results of using other Comparable members of the class. Below is a pretty typical

I want to do something like this: class Foo extends Ordered[Foo] { val x val y val z . . . . def compare(that: Foo) = { val c0 = this.length compareTo that.length // primary comparison lazy val c1 = this.x compareTo that.x // secondary comparison lazy val c2 = this.y.size compareTo that.y.size // tertiary comparison lazy val c3 = this.z.head compareTo that.z.head // final tie breaker if (c0 != 0) c0 else if (c1 != 0) c1 else if (c2 != 0) c2 else if (c3 != 0) c3 else c4 } } I was wondering if there was any cleaner way to write this kind of thing. I am expecting some thing like Ordering

I posted some code here which correctly solved a problem the poster had. OP wanted to remove duplicates and bring certain special items to the top of a list. I used a TreeSet with a special Comparable class which wrapped the Locale they were working with to achieve what they wanted. I then got to thinking ... as you do ... that I was eliminating duplicates by returning 0 from the compareTo method, not by returning true from an equals implementation as one would need to do to correctly indicate a duplicate in a Set (from the definition of a Set ). I have no objection to using this technique but

It is said that when input parameter is null, compareTo() should throw a NullPointerException. However, I am implementing a class which needs to compare fields with the type of String. These fields need not to be mandatory. I wonder in this case, 1) What should I return when the input is null? Should any not-null strings lexicographically bigger or smaller than null? and 2) If this is considered bad practice, is there any supporting arguments? Should I force the user to use empty strings instead? If using empty string, won't that confuse the case in which the field is not applicable and the