hashcode

问题 I have a cache based on Dictionary<MethodBase, string> The key is rendered from MethodBase.GetCurrentMethod. Everything worked fine until methods were explicitly declared. But one day it is appeared that: Method1<T>(string value) Makes same entry in Dictionary when T gets absolutely different types. So my question is about better way to cache value for generic methods. (Of course I can provide wrapper that provides GetCache and equality encountered generic types, but this way doesn't look

问题 I believe I read somewhere people generating equals / hashcode / toString methods during compile time (using APT) by identifying which fields should be part of the hash / equality test. I couldn't find anything like that on the web (I might have dreamed it ?) ... That could be done like that : public class Person { @Id @GeneratedValue private Integer id; @Identity private String firstName, lastName; @Identity private Date dateOfBirth; //... } For an entity (so we want to exlude some fields,

问题 Consider the following code: struct Vec2 : IEquatable<Vec2> { double X,Y; public bool Equals(Vec2 other) { return X.Equals(other.X) && Y.Equals(other.Y); } public override bool Equals(object obj) { if (obj is Vec2) { return Equals((Vec2)obj); } return false; } // this will return the same value when X, Y are swapped public override int GetHashCode() { return X.GetHashCode() ^ Y.GetHashCode(); } } Beyond the conversation of comparing doubles for equality (this is just demo code), what I am

问题 Consider the following code: struct Vec2 : IEquatable<Vec2> { double X,Y; public bool Equals(Vec2 other) { return X.Equals(other.X) && Y.Equals(other.Y); } public override bool Equals(object obj) { if (obj is Vec2) { return Equals((Vec2)obj); } return false; } // this will return the same value when X, Y are swapped public override int GetHashCode() { return X.GetHashCode() ^ Y.GetHashCode(); } } Beyond the conversation of comparing doubles for equality (this is just demo code), what I am

问题 I was playing around with Dictionary and stumbled across the below scenario public class MyObject { public string I { get; set; } public string J { get; set; } public string K { get; set; } public override int GetHashCode() { int hashCode = (I+J+K).GetHashCode(); Debugger.Log(9, "INFO", hashCode.ToString() + System.Environment.NewLine); return hashCode; } } class Program { static void Main(string[] args) { MyObject obj1 = new MyObject() { I = "Hello", J = "World" }; MyObject obj2 = new

问题 If I have a map and an object as map key, are the default hash and equals methods enough? class EventInfo{ private String name; private Map<String, Integer> info } Then I want to create a map: Map<EventInfo, String> map = new HashMap<EventInfo, String>(); Do I have to explicitly implement hashCode() and equals()? Thanks. 回答1: Yes, you do. HashMap s work by computing the hash code of the key and using that as a base point. If the hashCode function isn't overriden (by you), then it will use the

问题 The HashSet class has an add(Object o) method, which is not inherited from another class. The Javadoc for that method says the following: Adds the specified element to this set if it is not already present. More formally, adds the specified element e to this set if this set contains no element e2 such that (e==null ? e2==null : e.equals(e2)) . If this set already contains the element, the call leaves the set unchanged and returns false . In other words, if two objects are equal, then the

问题 So I asked another related question here: java string hash function with avalanche effect, but I have a different, related question now. What I established in that question was that the hashCode() function for String does not have an avalanche effect. This means, for example, that if I have strings "k1", "k2", "k3", and I call hashCode() on each, the values returned will be contiguous. Now, based on my recollection of data structures 101, I was under the impression that this is a bad thing.

问题 Edit: Prepare my objects for the use within a HashMap. after reading a bit about how to generate a hash code, im kind of confused now. My (probably trivial) question is, how should I implement a hashCode method when I have one field that I could use? Can I use the fiels directly? If I understand correctly, the values for hashCode must not change during the lifetime of an object, and I only have an ID filed that fits this, but I have read otherwhere, that one should not use ID...despide of

问题 It is well known that comparing floats by == is usually a mistake. In a 3D-vector class (with float components X, Y, Z) i wrote, two vectors are considered equal if their distance is considered zero. public override bool Equals(object obj) { if (obj == null) { return false; } if (GetType () != obj.GetType ()) { return false; } float d = DistSq ((Vec) obj); return IsConsideredZero (d); } public float DistSq(Vec p) { Vec d = this - p; return d.LengthSq (); } public float LengthSq() { return X *