equality

问题 This question already has answers here : Closed 7 years ago . Possible Duplicate: Understanding NSString comparison in Objective-C Was just reading up about equality vs identity and I realized that I've been using some equal signs when comparing strings in my objc code. The weird thing is that it actually works from times to times and I was wondering why. http://www.karlkraft.com/index.php/2008/01/07/equality-vs-identity/ I have two pieces of code, one work and one doesn't. WORKING. Here I

问题 I have a function that returns equalities, which I want to print, for example, x==y, or 2x+5==10. These usually have no meaning for mathematica, it cannot simplify it furhter. However, sometimes the both sides are equal, but I want to be able to print the equality in unevaluated form: that is, I want Mathematica to print x==x, and not True. A very simple example: Print[printableEqual[x,y]] should print x==y, while Print[printableEqual[x,x]] should print x==x Edit: The reason is that I have a

问题 I am trying to make a boolean test so that if one of the tire pressures is below 35 or over 45 the system outputs "bad inflation". In my class I must use a boolean, which is what I tried. However the boolean returned is always true. I don't understand why. public class tirePressure { private static double getDoubleSystem1 () //Private routine to simply read a double in from the command line { String myInput1 = null; //Store the string that is read form the command line double numInput1 = 0; /

问题 class L(object): def __eq__(self, other): print 'invoked L.__eq__' return False class R(object): def __eq__(self, other): print 'invoked R.__eq__' return False left = L() right = R() With this code, left side gets the first shot at comparison, as documented in the data model: >>> left == right invoked L.__eq__ False But if we make a slight modification on line 6 (everything else the same): class R(L): Now the right side gets to have the first shot at comparison. >>> left == right invoked R._

问题 I have found quote from jls: The equality operators may be used to compare two operands that are convertible (§5.1.8) to numeric type, or two operands of type boolean or Boolean, or two operands that are each of either reference type or the null type . All other cases result in a compile-time error. But this code String str= ""; Number num = 1; System.out.println(str == num); every operand is reference! said that it is incompatible types. Where did in jls say that these types should be

问题 I have found quote from jls: The equality operators may be used to compare two operands that are convertible (§5.1.8) to numeric type, or two operands of type boolean or Boolean, or two operands that are each of either reference type or the null type . All other cases result in a compile-time error. But this code String str= ""; Number num = 1; System.out.println(str == num); every operand is reference! said that it is incompatible types. Where did in jls say that these types should be

问题 I am trying to compare two JSON Strings for equality. I found this solution which uses Jackson as shown below but in all my project I am using GSON so I need to do the same thing using GSON. ObjectMapper mapper = new ObjectMapper(); JsonNode tree1 = mapper.readTree(jsonString1); JsonNode tree2 = mapper.readTree(jsonString2); if (tree1.equals(tree2)) { // yes, contents are equal -- note, ordering of arrays matters, objects not } else { // not equal } Is there any way to compare two JSON String

问题 I want to prove or falsify forall (P Q : Prop), (P -> Q) -> (Q -> P) -> P = Q. in Coq. Here is my approach. Inductive True2 : Prop := | One : True2 | Two : True2. Lemma True_has_one : forall (t0 t1 : True), t0 = t1. Proof. intros. destruct t0. destruct t1. reflexivity. Qed. Lemma not_True2_has_one : (forall (t0 t1 : True2), t0 = t1) -> False. Proof. intros. specialize (H One Two). inversion H. But, inversion H does nothing. I think maybe it's because the coq's proof independence (I'm not a

问题 How do you handle object equality for java objects managed by hibernate? In the 'hibernate in action' book they say that one should favor business keys over surrogate keys. Most of the time, i do not have a business key. Think of addresses mapped to a person. The addresses are keeped in a Set and displayed in a Wicket RefreshingView (with a ReuseIfEquals strategy). I could either use the surrogate id or use all fields in the equals() and hashCode() functions. The problem is that those fields

问题 What's your approach on writing equality checks for the structs and classes you create? 1) Does the "full" equality checking require that much of boilerplate code (like override Equals , override GetHashCode , generic Equals , operator== , operator!= )? 2) Do you specify explicitly that your classes model the IEquatable<T> interface? 3) Do I understand correctly, that there is no actual way to automatically apply Equals overrides, when I invoke something like a == b and I always have to