equals

I am trying accomplish the LINQ query below but I need a "not equal" instead of equal, so that filteredEmployees has all employees from groupA minus groupB. List<Employee> groupA = getEmployeeA(); List<Employee> groupB = getEmployeeB(); var filteredEmployees = from a in groupA join b in groupB on a.Name equals b.Name select a; You don't need a join for that: var filteredEmployees = groupA.Except(groupB); Note that this will be a sequence of unique employees - so if there are any duplicates in groupA , they will only appear once in filteredEmployees . Of course, it also assumes you've got a

I want to write an if/else statement that tests if the value of a text input does NOT equal either one of two different values. Like this (excuse my pseudo-English code): var test = $("#test").val(); if (test does not equal A or B){ do stuff; } else { do other stuff; } How do I write the condition for the if statement on line 2? Think of ! (negation operator) as "not", || (boolean-or operator) as "or" and && (boolean-and operator) as "and". See Operators and Operator Precedence . Thus: if(!(a || b)) { // means neither a nor b } However, using De Morgan's Law , it could be written as: if(!a &&

The contract of equals with regards to null , is as follows: For any non-null reference value x , x.equals(null) should return false . This is rather peculiar, because if o1 != null and o2 == null , then we have: o1.equals(o2) // returns false o2.equals(o1) // throws NullPointerException The fact that o2.equals(o1) throws NullPointerException is a good thing, because it alerts us of programmer error. And yet, that error would not be catched if for various reasons we just switched it around to o1.equals(o2) , which would just "silently fail" instead. So the questions are: Why is it a good idea

Many of my questions here on SO concerns IEquatable implementation. I found it being extremely difficult to implement correctly, because there are many hidden bugs in the naïve implementation, and the articles I found about it are quite incomplete. I want to find or write a definitive reference which must include: How to implement IEquatable correctly How to override Equals correctly How to override GetHashCode correctly How to implement the ToString method correctly How to implement the operator == correctly How to implement the operator != correctly Such a complete reference already exists?

I've been working with JPA (implementation Hibernate) for some time now and each time I need to create entities I find myself struggling with issues as AccessType, immutable properties, equals/hashCode, ... . So I decided to try and find out the general best practice for each issue and write this down for personal use. I would not mind however for anyone to comment on it or to tell me where I'm wrong. Entity Class implement Serializable Reason: The specification says you have to, but some JPA providers do not enforce this. Hibernate as JPA provider does not enforce this, but it can fail

How should I implement hashCode() and equals() for the following class in Java? class Emp { int empid ; // unique across all the departments String name; String dept_name ; String code ; // unique for the department } jutky in Eclipse right mouse click-> source -> generate hashCode() and equals() gives this: /* (non-Javadoc) * @see java.lang.Object#hashCode() */ @Override public int hashCode() { final int prime = 31; int result = 1; result = prime * result + (code == null ? 0 : code.hashCode()); return result; } /* (non-Javadoc) * @see java.lang.Object#equals(java.lang.Object) */ @Override

I'm a bit confused about the way Java treats == and equals() when it comes to int , Integer and other types of numbers. For example: Integer X = 9000; int x = 9000; Short Y = 9000; short y = 9000; List<Boolean> results = new ArrayList<Boolean>(); // results.add(X == Y); DOES NOT COMPILE 1) results.add(Y == 9000); // 2) results.add(X == y); // 3) results.add(X.equals(x)); // 4) results.add(X.equals(Y)); // 5) results.add(X.equals(y)); // 6) System.out.println(results); outputs (maybe you should make your guess first): [true, true, true, false, false] That X == Y does not compile is to be

I've been looking for a method that operates like Arrays.equals(a1, a2) , but ignoring the element order. I haven't been able to find it in either Google Collections (something like Iterables.elementsEqual() , but that does account for ordering) and JUnit ( assertEquals() obviously just calls equals() on the Collection, which depends on the Collection implementation, and that's not what I want) It would be best if such a method would take Iterable s, but I'm also fine with simply taking Collection s Such a method would of course take into account any duplicate elements in the collection (so it

According to the groovy docs , the == is just a 'clever' equals() as it also takes care of avoiding NullPointerException. So, the == and equals() should return the same value if the objects are not null. However, I'm getting unexpected results on executing the following script: println "${'test'}" == 'test' println "${'test'}".equals('test') The output that I'm getting is true false An example of this can be found here . Is this a known bug related to GStringImpl or something that I'm missing? Nice question, the surprising thing about the code above is that println "${'test'}".equals('test')