java hashcode and equals contract

Default equal implementation:The equal defined in the object class is only a reference judgment. If the two instances are referenced differently, the logic is also different.Equal customization implementation:However, two instances are different, but they are logically the same. For example, the date of some value objects and the user retrieved in oau2. if the UID of these user objects is the same, the logic is considered equal.Keywords: Same logic Equal uses getclass: If instanceof is not use

classes that do not override the two methods. string equals () The same is true if the memory address is the same and the content is the same.The storage address is different to satisfy the length, the hash code, the corresponding characters are the same to return true. hashcode of String () @Override public int hashcode () { int hash =

Hashcode method, the first hashcode comparison, if different, that does not need to be in the comparison of equals, so significantly reduce the equals comparison The number of times, this contrast needs to compare the number of significant efficiency improvement is very obvious, a good example is the use of the set;

The Equalsbuilder and Hashcodebuilder classes in the Apache Commons Lang Library can simplify the process of rewriting the equals and Hashcode methods in the Java class. The effective Java book provides an effective way to change the Equals and

1.Object classThe object class is the parent class for all classes in Java, and all classes in Java are directly or indirectlyInherit from Object classThere are not many methods defined in object, because Java has a variety of classes, their totalNot much, object only defines the commonalities that all classes should haveAll classes are subclasses of object, so a

Java object objects have 9 methods, which equals() and hashCode() in the implementation of HASHMAP play a more important role, I studied the source of HashMap, I met them, this blog is mainly to record their love between the killing.In order to illustrate their relationship, we need hashmap background knowledge.How the HashMap is storedHashMap is implemented as a

+ AreaCode; * result + prefix; * result + linenumber; return result;}Now, using the previous test code, I found that I was able to return Jenny.If a class is immutable and the cost of calculating the hash code is large, you should consider caching the hash code inside the object instead of recalculating the hash code every time the request is made, and if most of these objects are used as hash keys, you should calculate the hash code when the instance is created, or you can choose

(INT Arg, int Max, string name ){If (ARG }Public Boolean Equals (Object O ){If (O = This) reutrn true;If (! (O instanceof phonenumber) return false;Phonenumber Pn = (phonenumber) O;Return Pn. Extension = extension Pn. Exchange = exchange Pn. areacode = areacode;}// No Hashcode Method...}There are currently the following lines of programs:Map M = new hashmap ();M. Put (New phonenumber (1, 2, 3), "Jenny ")

Equals (), hashcode (), Cloning learning experienceIn fact, in the development time, rarely to rewrite the Equals (), Hashcode () method, but sometimes the business needs to be rewritten.Attention:Overriding the Equals () method is sure to override the

A rule in Java that determines whether two objects are equal:First, determine whether the hashcode of two objects is equalIf not equal, neither object is considered equalIf equal, determine whether two objects are equal with the equals operationIf not equal, neither object is considered equalIf equal, two objects are considered equalWe need a downward transformat

2015 "Oracle Cup" national Java Program Design Competition-pre-match simulation from the Competition Test Network (http://www.jingkao.net/)Review the overrides of the Equals () and hashcode () classesWhat is rewriting?(1) The polymorphism between the parent class and the child class, redefining the function of the parent class. If you define a method in a subclas

Hashcode and equals are two methods in the object class, where hashcode () is a local method. (1) hashcode (): returns an integer Hash Value, which is used in hashmap, hashtable, and other classes. For example, in hashmap, compare keys for consistency. e.hash == hash ((k = e.key) == key || key.equals(k)) When using o

Equals () is A method provided by the object class, and it is well known that each Java class inherits from Object, So every object has a equals () method, which we generally override when we use this method.The equals () method in the Object class source code Public Boolean e