immutability

问题 String s1 = "String1"; System.out.println(s1.hashCode()); // return an integer i1 Field field = String.class.getDeclaredField("value"); field.setAccessible(true); char[] value = (char[])field.get(s1); value[0] = 'J'; value[1] = 'a'; value[2] = 'v'; value[3] = 'a'; value[4] = '1'; System.out.println(s1.hashCode()); // return same value of integer i1 Here even after I changed the characters with the help of reflection, same hash code value is mainatained. Is there anything I need to know here?

问题 I'm in the process of trying to 'learn more of' and 'learn lessons from' functional programming and the idea of immutability being good for concurrency, etc. As a thought exercise I imagined a simple game where Mario-esq type character can run and jump around with enemies that shoot at him... Then I tried to imagine this being written functionally using immutable objects. This raised some questions that puzzled me (being an Imperative OO programmer). 1) If my little guy at position x10,y100

问题 I am developing an app that creates a large number of small, immutable Java objects. An example might be: public class Point { final int x; final int y; final int z; ..... } Where it is likely that many instances of Point will need to refer to the same (x,y,z) location. To what extent does it make sense to try to cache and re-use such objects during the lifetime of the application? Any special tricks to handle this kind of situation? 回答1: The problem you are likely to have is making the

问题 This question already has answers here : Is there a way to compare lambdas? (3 answers) Closed 4 years ago . I am not sure how I can be sure about equality/immutability of functional interface. I guess there might be no way to assure equality when I use this syntactic sugar in java 8, please let me know any hint if you have any. I made a short code snippet for my question. public interface Element { void doSomething(int a); } and I've tried to add instance of this interface in functional way

问题 The question is simple. Can a type that can change its internal state without it being observable from the outside be considered immutable ? Simplified example: public struct Matrix { bool determinantEvaluated; double determinant; public double Determinant { get //asume thread-safe correctness in implementation of the getter { if (!determinantEvaluated) { determinant = getDeterminant(this); determinantEvaluated = true; } return determinant; } } } UPDATE : Clarified the thread-safeness issue,

问题 I am trying to figure out whether the following are immutable in Sage (which is built on Python so I believe if it is immutable in python, I believe in most cases it will be immutable in Sage) Below are objects e, f, g, i class e: pass f = e() g = pi # (g's "type" in Sage is symbolic expression. It's supposed to be 3.1415....etc) i = lambda x: x*x I gather that e is a class which means it is mutable (Does an immutable class make sense? Can't all classes be modified?). Since f is an instance

问题 Experiencing some unexpected performance from Microsoft ImmutableList from NuGet package Microsoft.Bcl.Immutable version 1.0.34 and also 1.1.22-beta When removing items from the immutable list the performance is very slow. For an ImmutableList containing 20000 integer values (1...20000) if starting to remove from value 20000 to 1 it takes about 52 seconds to remove all items from the list. If I do the same with a generic List<T> where I create a copy of the list after each remove operation it

问题 I've discovered a strange behavior for mutable sets which I cannot understand: I have a object which I want to add to a set. The equals method for the class is overridden. When I add two different objects to the set, which produces the same output for equals method, I get a different behavior between mutable and immutable sets for the contains method. Here is the code snippet: class Test(text:String){ override def equals(obj:Any) = obj match { case t: Test => if (t.text == this.text) true

问题 In the book Java Concurrency In Practice it explains the advantages of "effectively immutable" objects versus mutable objects concurrency-wise. But it does not explain what advantage "effectively immutables" objects would offer over really immutable objects. And I don't get it: can't you always build a really immutable object at the moment you'd decide to publish safely an "effectively immutable" object? (instead of doing your "safe publication" you'd build a really immutable object and that

问题 I want a string with one additional attribute, let's say whether to print it in red or green. Subclassing(str) does not work, as it is immutable. I see the value, but it can be annoying. Can multiple inheritence help? I never used that. Inheriting only object and using self.value=str means I have to implement all string-ness messages (like strip) myself. Or is there a way to forward them, like Ruby's missing_method? I think using a class-level dictionary indexed by instance to store the color