Download Equals Movie
Stefania Bahrke
The general contract of hashCode is:
- Whenever it is invoked on the same object more than once during an execution of a Java application, the hashCode method must consistently return the same integer, provided no information used in equals comparisons on the object is modified. This integer need not remain consistent from one execution of an application to another execution of the same application.
- If two objects are equal according to the equals(Object) method, then calling the hashCode method on each of the two objects must produce the same integer result.
- It is not required that if two objects are unequal according to the equals(java.lang.Object) method, then calling the hashCode method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hash tables.
The equals method for class Object implements the most discriminating possible equivalence relation on objects; that is, for any non-null reference values x and y, this method returns true if and only if x and y refer to the same object (x == y has the value true).
I'm still pretty fresh to all this, but I'm working on attaining my OCAJP certification (Java). I remembered reading previously that the .equals method could be overridden when I came to this question:
This got me thinking, is that true? I mean, if I get the question on the exam, I know how to answer it now, but in the deep dark abyss of overriding madness, is it possible to create a situation where a.equals(a) returns false? I feel like this would make Aristotle angry...
This question, however, specifically says that these are primitive wrappers (e.g. Integer, Boolean, etc.) and since these classes are final, you cannot extend them, thus a.equals(a) will always return true.
One example: Java's own Collection classes (java.util.Collection and friends) rely on equals. If an instance of a class that does not correctly implement equals is put into a collection, weird things happen, such as the collection sometimes containing the instance and sometimes not.
You can take a look at the implementations of all the primitive wrappers , i.e: Integer, Boolean, Character etc... you will see that the implementation is correct.
The reason is that with equals, once of the checks being done is to check reference equality, and x.equals(x) as the both object and the argument are the same object.
General question: When implementing an override of the default equals method in Java, what concerns should I have about simply utilizing an already implemented compareTo method vs writing independent logic into the equals method? I noticed someone mention in another question that foo.equals((String)null) returns false whereas String.compareTo((String)null) throws a NullPointerException. What makes these inconsistent results ideal functionality?
The natural ordering for a class C is said to be consistent with equals if and only if e1.compareTo(e2) == 0 has the same boolean value as e1.equals(e2) for every e1 and e2 of class C. Note that null is not an instance of any class, and e.compareTo(null) should throw a NullPointerException even though e.equals(null) returns false
Ergo, since null.compareTo(x) obviously throws a NPE, x.compareTo(null) should throw a NPE as well. Whereas for equals, that is not necessarily the case. I am pretty big on the proper handling of NPEs, so I find this relatively significant.
The difference between equals() and compareTo() is that equals() just checks if two objects are equal to each other where the compareTo() is used to identify the natural order of the instances of specified class. Also equals() method has a contract with hashCode() method but compareTo() hasn't.
It is strongly recommended, but not strictly required that (x.compareTo(y)==0) == (x.equals(y)). Generally speaking, any class that implements the Comparable interface and violates this condition should clearly indicate this fact. The recommended language is "Note: this class has a natural ordering that is inconsistent with equals."
You can feel free to reuse compareTo() method logic in your equals() method but keep in mind all the contracts to the equals(), hashCode() and contract from JavaDoc for compareTo() method. If they do not conflict with each other then go ahead.
RW Eisinger, CW Dieffenbach, AS Fauci. HIV viral load and transmissibility of HIV infection: undetectable equals untransmittable. Journal of the American Medical Association DOI: 10.1001/jama.2018.21167 (2019).
Objectives: 'Undetectable equals Untransmittable' (U=U) is an empowering message that may enable people living with HIV (PLHIV) to reach and maintain undetectability. We estimated the percentage of PLHIV who ever discussed U=U with their main HIV care provider, and measured associations with health-related outcomes. Secondarily, we evaluated whether the impact of the U=U message varied between those who heard it from their healthcare provider (HCP) vs from elsewhere.
All of these have the potential of inflating the respective library's numbers in comparison to fast-equals, but it was the closest apples-to-apples comparison I could create of a reasonable sample size. It should be noted that react elements can be circular objects, however simple elements are not; I kept the react comparison very basic to allow it to be included.
So I currently have a custom attributes where I need to check parameters if not equals to the set attribute but I want the condition to be case insensitive. And it seems like using != operator doesn't work that way.
Eye health equals opportunity, allowing children to learn and adults to earn. It equals improved wellbeing: supporting families, communities and nations to thrive. And it equals progress towards reducing poverty and inequality.
Note that most code, for example all collections, handle our persons as objects and thus always call equals(Object). So we better make sure we provide an implementation with that signature! We can of course create a specialized equals implementation and call it from our more general one if we like that better.
We have seen how to properly implement equals (and will soon look at hashCode). But what if we are using classes that we have no control over? What if their implementations of these methods do not suit our needs or are plain wrong?
However, this way of thinking implies that the equality comparisons form a one-dimensional "spectrum" where "totally strict" lies on one end and "totally loose" lies on the other. This model falls short with Object.is, because it isn't "looser" than double equals or "stricter" than triple equals, nor does it fit somewhere in between (i.e., being both stricter than double equals, but looser than triple equals). We can see from the sameness comparisons table below that this is due to the way that Object.is handles NaN. Notice that if Object.is(NaN, NaN) evaluated to false, we could say that it fits on the loose/strict spectrum as an even stricter form of triple equals, one that distinguishes between -0 and +0. The NaN handling means this is untrue, however. Unfortunately, Object.is has to be thought of in terms of its specific characteristics, rather than its looseness or strictness with regard to the equality operators.
However, this way of thinking implies that the equality comparisons form a one-dimensional \"spectrum\" where \"totally strict\" lies on one end and \"totally loose\" lies on the other. This model falls short with Object.is, because it isn't \"looser\" than double equals or \"stricter\" than triple equals, nor does it fit somewhere in between (i.e., being both stricter than double equals, but looser than triple equals). We can see from the sameness comparisons table below that this is due to the way that Object.is handles NaN. Notice that if Object.is(NaN, NaN) evaluated to false, we could say that it fits on the loose/strict spectrum as an even stricter form of triple equals, one that distinguishes between -0 and +0. The NaN handling means this is untrue, however. Unfortunately, Object.is has to be thought of in terms of its specific characteristics, rather than its looseness or strictness with regard to the equality operators.
8d45195817