java hashcode and equals contract

I need to record some of the things I saw in Sunday, or I will forget. Hashcode, equals: 1 Each Java object has a hashcode and equals method. The ultimate Java class is the object class, so how does the object class label itsel

Today to interview, I always feel that I understand everything, should not be a problem, when asked "not overridden by the Equals () method and the Hashcode () method inside the content is. Why do I need to override the Hashcode () method while rewriting the Equals () method? When, to tell the truth, a face Meng Ah ...

); Sbset.add (HELLOSB); Sbset.add (HELLO2SB); Person Person1 = new person (1, "eke"); Person Person2 = new person (1, "eke"); Set personset = new HashSet (); Personset.add (Person1); Personset.add (Person2); Personwithhashcode code1 = new PersonwithhashCode (1, "eke"); Personwithhashcode Code2 = new Personwithhashcode (1, "eke"); Set codeset = new HashSet (); Codeset.add (CODE1); Codeset.add (CODE2); System.out.p

The following content is summarized in objective Java.1. When to rewrite equals ()When a class has its own unique concept of "logical equality" (different from the concept of object identity ).2. design equals ()[1] use the instanceof operator to check whether the real parameter is of the correct type ".[2] for each "key field" in the class, check the field value

in Java, = =, Equals (), and hashcode () are all related to the comparison of objects. about = == = is easy to understand. Java design Java is to compare two objects is not the same object.For reference variables, the two reference variables refer to the same object whe

method public int hashcode () {///return 1; This method can also be effective but calls the Equals method, and the comparison is much more//the method calls the Hashcode method of String, it does not call Equals method, less number of comparisons return Name.hashcode () +age*39; The uniqueness of the

object being stored, and O2 should be replaced with O1, but because O1.hashcode ()!=o2.hashcode (), ( The Hahscode method is called, and the hash list does not have an element at the address of the hash code, then the O1 is placed in the address. This resulted in the existence of two identical objects in the HashMap, violating the design principles of HashMap.2. In a hash list such as Hashmap,hashtable,has

equal to =, so in most cases it will still go to equals, so equals is equally important. To rewrite it, both of them will be overwritten ~ In fact, java has a convention on hashCode:1. during the execution of an application, if the information used for the equals Method Com

The use of map is usually a Java native type, so there is little focus on the internal implementation of the methods of Hashcode () and Equals (). The recent realization of a small tool, involving their own writing of the class lookup, and again revisit the relevant knowledge.On the simple example code, the difference between the overwrite and the non-overwriteDo

In project development, we all have this experience, that is, when adding a table, the corresponding increase in Java classes, in the Java class, there are a number of common methods, including: Equals (), Hashcode (), toString (), CompareTo () These four methods, For beginners who just touch

? objects.equals (hireday,other.hireday); } public int Hashcode () {the//objects.hash () method provides multiple parameters,//Call the Objects.hashcode () method on each parameter to get the respective hash value and combine the hash values. return Objects.hash (name,salary,hireday); } Public String toString () {return GetClass (). GetName () + "[name" +name+ "salary=" +salary+ "hireday=" +hireday+ "]"; } }Create employee sub-class managerP

Java =, equals (), hashCode () Source Code AnalysisComparison of = and equals () is often encountered in java programming or interviews. I looked at the source code and summarized it with the actual programming. 1. = in java, the

these person objects is the same, Object 1.equals (object 2) should return true, regardless of the position of object 1, Object 2 in memory!2, overriding equals Why rewrite hashcode?The reference blog post at the beginning of this article has already mentioned a reason. That is, since object 1.equals (object 2) return