equals

问题 In the equals() method of my class, I am using a private instance HashMap variable to compare for the equality. However, 2 different objects still show being equal when comparing their HashMap variables. Further research brought me to the link : Link Here . However, it just says that the reason for HashMap1.equals(HashMap2) not working is because " apparantly Java's arrays cannot be tested for equality without writing a customized code." I did not understand this reason. Can anyone please

问题 matches : Will check if the complete string entered is equal to the value present in the string object. equalsIgnoreCase : Ignoring the case, it checks if the string entered is equal to the value present in the string object. equals : Case sensitive and it checks if the string entered is equal to the value present in the string object. This is what I know about the methods, present in String class. Are there any other differences(Am I missing any valuable differences)? If there are no

问题 It is my understanding that two unequal objects can have the same hashcode. How would this be handled when adding or retrieving from a HashMap java? 回答1: They will just be added to the same bucket and equals() will be used to distinguish them. Each bucket can contain a list of objects with the same hash code. In theory you can return the same integer as a hash code for any object of given class, but that would mean that you loose all performance benefits of the hash map and, in effect, will

问题 As I study the source code of some open source products, I find code like: if (a=="cluser") a is a String variable. Can a String equals operation be replaced with == ? 回答1: You should almost never use == and almost always use equals() . It will only work with == if both strings reference the same object. There's an intern() method on String to return the same reference for a given string value. String literals are implicitly interned. Only if you have a very good reason should you use == for

问题 Imagine that we have this piece of code. public class HashAddAfter { private class A { public int value; public A(int value) { this.value = value; } public void setValue(int value) { this.value = value; } // Code for hashCode()... // Code for equals()... } Set<A> list1 = new HashSet<A>(); Set<A> list2 = new HashSet<A>(); public static void main(String[] args) { HashAddAfter x = new HashAddAfter(); A e1 = x.new A(1); A e2 = x.new A(1); x.list1.add(e1); x.list2.add(e2); System.out.println(x

问题 Check this out : var a = Double.NaN; Console.WriteLine(a == a); Console.ReadKey(); Prints "False" var a = Double.NaN; Console.WriteLine(a.Equals(a)); Console.ReadKey(); Prints "True"! Why it prints "True"? Due to floating point numbers specification, value that is NaN is not equal to itself! So it seems that Equals() method is implemented wrong... Am I missing something ? 回答1: I found an article addressing your question: .NET Security Blog: Why == and the Equals Method Return Different

问题 I'm well aware of the contractual needs to make sure that hashCode is consistent with equals and that equals is consistent with compareTo . However, this is often violated in practice. Are there any tools, techniques, or libraries that can test for this consistency automatically? I suspect unfortunately that the answer is "no," but it would be useful to be able to have a unit test for this sort of thing that could make use of a library call or framework rather than needing to write a custom

问题 What is the standard idiom for implementing the equals and hashCode methods in Scala? I know the preferred approach is discussed in Programming in Scala , but I don't currently have access to the book. 回答1: There's a free 1st edition of PinS that discuss this subject just as well. However, I think the best source is this article by Odersky discussing equality in Java. The discussion in PinS is, iirc, an abbreviated version of this article. 回答2: After doing quite a bit of research, I couldn't

问题 When I test this code: java.util.Date date = new java.util.Date(); java.util.Date stamp = new java.sql.Timestamp(date.getTime()); assertTrue(date.equals(stamp)); assertTrue(date.compareTo(stamp) == 0); assertTrue(stamp.compareTo(date) == 0); assertTrue(stamp.equals(date)); I´ll be expecting a true, true, true, false. Because of this: In the javadoc for java.sql.Timestamp, it states: Note: This type is a composite of a java.util.Date and a separate nanoseconds value. Only integral seconds are

问题 I read a line from a file: KatalogObrazków 1 32 Means that I should look for data in: C:\Users\NAME_OF_THE_USER/KatalogObrazków and so I do it, but there is horrible thing going on. In splitLine[0] I have a word "KatalogObrazków" but then the computer says that "KatalogObrazków".equals(splitLine[0]) is false, there is no whitespace arround splitLine[0] left after splitting line. Please have a look at the code below. BufferedReader br = new BufferedReader(new FileReader(path)); String line;