java hashcode and equals contract

Tips"Effective Java, third Edition" an English version has been published, the second edition of this book presumably many people have read, known as one of the four major Java books, but the second edition of 2009 published, to now nearly 8 years, but with Java 6, 7, 8, and even 9 of the release, the Java language has

(); System.out.println ("i = = I4 =" + (i = = i4)); System.out.println ("i4.equals (i) =" + (i4.equals (i))); ------------------------------ I1 = = I2 = true I1.equals (I2) = true i3 = = I4 = false I3.equals (i4) = true I2 = = I4 = false I2.equals (i4) =

.) {this.age = age; } @Override Public String toString () {return ' Student [name= + name + ", age=" + Age + "]"; } @Override public int hashcode () {final int prime = 31; int result = 1; result = Prime * result + age; result = Prime * result + ((name = = null)? 0:name.hashcode ()); return result; } @Override public boolean equals (Object obj) {if (this = = obj) retu

= count; for (int i = 0; i H = 31*h + val[off++];}hash = h;}return h;}It is not related to the memory address. This is done to ensure that two objects that are returned as true are compared with equals, and that their hashcode are the same.So when you rewrite equals, you rewrite Hashcode (). Of course, this is equival

Java-equal and hashCode, java-javashashcode Come to the end of the paper, and never know how to do this-Lu YouWenqu that clear such, for the source of live water to Zhu Xi Equals () is used to determine whether two objects are equal. In the Object class, equals (Object obj)

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

;for (int i = 0; i H = 31*h + val[off++];}hash = h;}return h;}It is not related to the memory address. This is done to ensure that two objects that are returned as true are compared with equals, and that their hashcode are the same.So when you rewrite equals, you rewrite Hashcode (). Of course, this is equivalent to a

agreement of Hashcode is: 1. During Java application execution, when the hashcode method is called multiple times on the same object, the same integer must be returned consistently, provided that the information used to compare the object to equals is not modified. The integer does not need to be cons

UnderstandThe function of Hashcode () is to get the hash code, also known as the hash code, which is actually returning an int integer. The purpose of this hash code is to determine the index position of the object in the hash table.Hashcode () is defined in the JDK's object.java, which means that any class in Java contains the hashcode () function.Although, each

HashCode and javahashcode for JAVA Learning public native int hashCode(); Returns the hash value of the object. This method is supported to improve the hash table (for examplejava.util.HashtableHash table.I. Role of HashCode We usually use equals to determine whether the set

The reason why we write hashcode, because usually we always hear it. But do you really know hashcode? Where will it be used? How should it be written?I believe reading this article, can let you see different hashcode.The purpose of using hashcode is to use one object to find another object. For data structures that use hashing, for example HashSet、HashMap、LinkedH

There are many people who have studied Java for a long time, but have not understood the role of the Hashcode method,Let me explain it to you. 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 o

Many people have learned Java for a long time, but have never understood the role of the hashCode method. Let me explain it. First, to understand the role of hashCode, you must first know the set in Java. In general, collections in Java have two types: List and Set. Do you k

Question: 1. In the Java API Doc, I saw the statement below: This integer need not remain consistent from one execution of an application to another execution of the same application. Does it mean that on each execution, the hashcode may be different?But I run this programme (fragment below) sereral times: System. Out. println ("C1 hashcode:" + c1.

:" + (Endtime-starttime) + "Ms."); }}In the above code, we have calculated the difference set for the list of length 2000,10000,50000, and time is as follows:list Remove all cost:46ms. 10000 list Remove all cost:1296ms. 50000 list Remove all cost:31028ms.As you can see, the amount of data increased by 5 times times, the ArrayList of the difference set operation time consumption increased by 30 times times. When we do the hundreds of thousands of-element differential set operation, the time consu

[n-1] S [I] is the ith character of the string; why use 31? Http://stackoverflow.com/questions/299304/why-does-javas-hashcode-in-string-use-31-as-a-multiplierThis formula ensures that the first character in the string has an impact on the last generated hashcode. 3. Custom class. If the override equals () method is used, the override

, that is, the same value must have the same hashcode values. This is also easy to understand, because the value values are the same, then the equals comparison is equal, the Equals method is equal, then the hashcode must be equal. The reverse is not necessarily true. It does not guarantee that the same

Many people have studied Java for a long time, but have not understood the role of the Hashcode method,Let me explain. First of all, to understand the role of hashcode, you have to know the collection in Java first.In general, the set in Java (Collection) has two classes, on

There are many people who have studied Java for a long time, but have not understood the role of the Hashcode method,Let me explain it to you. 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 o