equals

I have a simple base class, which is later extended by many separate classes, which potentially introduce new fields, but not necessarily. I defined an equals method in the base class, but also overriden that for a few subclasses. Is it OK to mix definitions in base/subclasses? In my case it was to avoid code duplication checking the same fields. Raph Take a look at "Implementing equals() To Allow Mixed-Type Comparison" from Angelika Langer . Here is a brief explanation of some problems and a possible solution: The equals contract says (amongst others): It is symmetric: for any non-null

I have integers that are supposed to be equal (and I verify it by output). But in my if condition Java does not see these variables to have the same value. I have the following code: if (pay[0]==point[0] && pay[1]==point[1]) { game.log.fine(">>>>>> the same"); } else { game.log.fine(">>>>>> different"); } game.log.fine("Compare:" + pay[0] + "," + pay[1] + " -> " + point[0] + "," + point[1]); And it produce the following output: FINE: >>>>>> different FINE: Compare:: 60,145 -> 60,145 Probably I have to add that point is defined like that: Integer[] point = new Integer[2]; and pay us taken from

From the JavaDoc of TreeMap : Note that the ordering maintained by a sorted map (whether or not an explicit comparator is provided) must be consistent with equals if this sorted map is to correctly implement the Map interface. (See Comparable or Comparator for a precise definition of consistent with equals.) This is so because the Map interface is defined in terms of the equals operation, but a map performs all key comparisons using its compareTo (or compare) method, so two keys that are deemed equal by this method are, from the standpoint of the sorted map, equal. The behavior of a sorted map

As far as I understand, Scala's == defines the natural equality of two objects. I expected that Array(0,1,2) == Array(0,1,2) compares the natural equality. For example, checks if all elements of the array return true when compared with the corresponding elements of the other array. People told me that Scala's Array is just a Java [] which only compares identity. Wouldn't it be more meaningful to override Array 's equals method to compare natural equality instead? Scala 2.7 tried to add functionality to Java [] arrays, and ran into corner cases that were problematic. Scala 2.8 has declared that

This question already has an answer here: Is there a difference between “==” and “is”? 15 answers String comparison in Python: is vs. == [duplicate] 4 answers I run the following in the Python interpreter: >>> foo = 10 >>> dir(foo) == dir(10) True >>> dir(foo) is dir(10) False >>> Why is this? is checks that 2 arguments refer to the same object, == checks that 2 arguments have the same value. dir() returns a list which contains the same data for both foo and 10 , but the actual list instances for the 2 things are different. 来源： https://stackoverflow.com/questions/15008380/double-equals-vs-is

I've read about 10 different questions on when and how to override GetHashCode but there's still something I don't quite get. Most implementations of GetHashCode are based on the hash codes of the fields of the object, but it's been cited that the value of GetHashCode should never change over the lifetime of the object. How does that work if the fields that it's based on are mutable? Also what if I do want dictionary lookups etc to be based on reference equality not my overridden Equals ? I'm primarily overriding Equals for the ease of unit testing my serialization code which I assume