Lien rompu dans énoncé TP

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Modérateur : douinj

moro_al
Messages : 22
Inscription : 01 oct. 2020 21:34

Lien rompu dans énoncé TP

Message par moro_al » 15 oct. 2020 22:35

Bonjour,

Le lien mis en aide sur la question 2-1 du TP3 http://www.javaworld.com/javaworld/jw- ... ct-p2.html
semble malheureusement non disponible désormais.

Ce lien peut il se substituer ?
https://www.infoworld.com/article/20763 ... bject.html

moro_al
Messages : 22
Inscription : 01 oct. 2020 21:34

Re: Lien rompu dans énoncé TP

Message par moro_al » 16 oct. 2020 0:13

Pour le coup le lien de substitution même si ce n'est pas le bon, donne de bonnes indications pour la méthode equals()

douinj
Messages : 153
Inscription : 18 mars 2009 15:46

Re: Lien rompu dans énoncé TP

Message par douinj » 16 oct. 2020 8:51

Bonjour et merci de me l'avoir signalé, et pour la référence, je modifierai l'énoncé en mettant ces liens sur la javadoc de la classe Object

Bons equals et hashcode

https://docs.oracle.com/javase/7/docs/ ... bject.html

méthode equals
public boolean equals(Object obj)

Indicates whether some other object is "equal to" this one.

The equals method implements an equivalence relation on non-null object references:

It is reflexive: for any non-null reference value x, x.equals(x) should return true.
It is symmetric: for any non-null reference values x and y, x.equals(y) should return true if and only if y.equals(x) returns true.
It is transitive: for any non-null reference values x, y, and z, if x.equals(y) returns true and y.equals(z) returns true, then x.equals(z) should return true.
It is consistent: for any non-null reference values x and y, multiple invocations of x.equals(y) consistently return true or consistently return false, provided no information used in equals comparisons on the objects is modified.
For any non-null reference value x, x.equals(null) should return false.

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).

Note that it is generally necessary to override the hashCode method whenever this method is overridden, so as to maintain the general contract for the hashCode method, which states that equal objects must have equal hash codes.
public int hashCode()

Returns a hash code value for the object. This method is supported for the benefit of hash tables such as those provided by HashMap.

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.

As much as is reasonably practical, the hashCode method defined by class Object does return distinct integers for distinct objects. (This is typically implemented by converting the internal address of the object into an integer, but this implementation technique is not required by the JavaTM programming language.)

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