hashcode and equals in java

1. If the equals two objects are the same, then the hashcode must be the same.2, Hashcode same, two objects equals is not necessarily the same. (hash collisions may occur)In order to improve the efficiency of the implementation of the Hashcode method, first hash, if differen

Both are methods, inherited from the object class, andthe equals method in object compares this is the same as the reference address of the object passed in by the parameter, so the necessary sufficient condition for theequals return value to true is that the two point to the same object, then Hashcode are the same. The above is said that the equals method is

;}public void Setsid (String sid) {This.sid = SID;}}Package com.test.entity;Import Java.util.Date;Import Javax.persistence.Column;Import Javax.persistence.EmbeddedId;Import javax.persistence.Entity;Import javax.persistence.Table;@Table (name= "test")@Entitypublic class Test1 {@Column (name= "date")private date date;@EmbeddedIdPrivate TESTPK TESTPK;Public Date getDate () {return date;}public void SetDate (date date) {This.date = date;}Public TESTPK GETTESTPK () {return TESTPK;}public void Settest

By default, the equals method inherited from a super-class object is equivalent to the '=' method. The memory address of the object is compared, but we can override the equals method, make it compare according to our needs. For example, the string class overwrites the equals method so that it compares the Character Sequence instead of the memory address.Hashcode

; - PrivateString PropertyName;//Sort Properties - PrivateBoolean ISASC;//whether the positive order the - PublicInteger Getorderno () { - returnOrderNo; - } + - Public voidSetorderno (Integer orderno) { + This. OrderNo =OrderNo; A } at - PublicString Getpropertyname () { - return This. PropertyName; - } - - Public voidSetpropertyname (String PropertyName) { in This. PropertyName =PropertyName; - } to + Publ

ToString ()----------------------The value of the output object after the address of the output object is rewritten object. Equals (object)---------------Compare the memory address overrides of two objects by comparing the properties of two objects (always overriding the Hashcode () method, because instance ab behaves equal by Equals, But they exist in the HashM

1 ImportJava.util.*;2 3 Public classTest {4 Public Static voidMain (string[] args) {5Collection C =NewHashSet ();6C.add ("Hello");7C.add (NewName ("Lovy", "Winsy"));8C.add (NewInteger (100));9C.remove ("Hello");TenC.remove (NewInteger (100)); OneC.remove (NewName ("Lovy", "Winsy")); A System.out.println (C.size ()); - System.out.print (c); - } the } - - className { - PrivateString FirstName; + PrivateString LastName; - + PublicName (String firstName, String lastName) { A

The following are covered:public class User{Private Integer ID;Private String UserName;Private String PassWord;Public Integer getId () {return ID;}public void SetId (Integer id) {This.id = ID;}Public String GetUserName () {return userName;}public void Setusername (String userName) {This.username = UserName;}Public String GetPassword () {return PassWord;}public void SetPassword (String passWord) {This.password = PassWord;}@Overridepublic boolean equals

Things that are generally described need to be added to the collection, both methods need to be rewritten Delete and determine whether the existence of elements, are first judged hashcode to see if there is, if there is continued equals (); Import java.util.*; Class Person {private String name; private int age; Person (String Name,int age) {this.name=name; This.age=age; The public int

A Brief Introduction to the correct method for evaluating hashCode in Java and the value of hashcode This article focuses on the relevant content of the correct hashCode Evaluate Method in Java, as detailed below. The hash list has an optimization function to cache the

Let's take a look at the example [java] package equalhashcode; import java. util. *; import bad. newFileSize; class Person {private String username; private int age; public Person () {} public Person (String username, int age) {this. username = username; this. age = age;} public String getUsername () {return username;} public void setUsername (String username) {this. username = username;} public int getAge

) = true I = i2 = true I1.equals (I) = true I = i4 = true I4.equals (I) = true 3> hashcode and equals of the object1) to understand the role of hashcode, we can understand it in java. lang. Object. Every time a new JVM Object is

comparison reference is the same).Hashcode () is a local method, and its implementation is dependent on the local machine.2. The Java language requirements for Equals () are as follows, and these requirements must be followed:A symmetry: If X.equals (y) returns "true", then Y.equals (x) should also return "true".B reflectivity: x.equals (x) must return is "true"

Introduction to the hashcode method in Java The hash table data structure is certainly not unfamiliar to most people, and hash tables are used in many places to improve the search efficiency. There is a method in the Object class of Java: public native int hashCode(); According to the declaration of this method, this m

Hash table This data structure presumably most people are not unfamiliar, and in many places will use hash tables to improve the search efficiency. There is a method in the object class in Java:public native int hashcode ();According to the declaration of this method, the method returns a numeric value of type int and is a local method, so no specific implementation is given in the object class.Why does the object class need such a method? What role d

On the Hashcode method in Java Hash table This data structure presumably most people are not unfamiliar, and in many places will use hash tables to improve the search efficiency. There is a method in the object class in Java: public native int hashcode (); Why does the object class need such a method? What role does it

A hash table This data structure must be familiar to most people, and in many places, hash tables are used to improve search efficiency. There is a method in the Java object class: According to the declaration of this method, the method returns a numeric value of type int and is a local method, so no specific implementation is given in the object class. Why does the object class need such a method? How does it work? Today we will discus

into the collection, how do you determine if the object already exists in the collection? Perhaps most people would have thought of calling the Equals method to make comparisons on a case by case basis. However, if there are already 10,000 or more data in the collection, if the Equals method is used to compare each other, efficiency must be a problem. At this point the function of the

First, to understand the role of hashcode, you must first know the collection in Java.In general, there are two types of collections (Collection) in Java, one is list, and the other is set. Do you know the difference between them? The elements within the set are ordered, the elements can be repeated, the latter elements are unordered, but the elements are not repeatable. So here is a more serious problem: t

First, why should have hash algorithmThere are two types of collections in Java , one is list, and the other is set. The elements in the list are ordered and the elements can be duplicated. The set element is unordered, but the element is not repeatable. If you want to ensure that the elements are not duplicated, should the two elements be repeated according to what to judge? Use the Object.Equals method. However, if each additional element is checked