comparison of the values in the class, do not directly compare two values with equals, for example:Double A = 1;Double b = 1;System.out.prinln (A.equals (b)); It is clear that this statement is wrong.The Java language has the following requirements for Equals ():A: Symmetry: if X.equals (y) returns "true", then Y.equals (x) should also return "true".B: reflectiv
Note hashcode only when hashtable, hashmap, hashset, and linkedhashmap are used. hashcode is useless in other places. (This is not necessarily true)
Whether two objects are equal requires that hashcode () be equal. Is the following statement true?
In a Java set, the rule for determining whether two objects are equal is
field in the object. Returns true if all of these tests are successful, otherwise false.5. After writing completes the Equals method, check for symmetry, transitivity, and consistency.3, HashcodeThe Hashcode () method returns a numeric value, as can be seen from the name of the method, and its purpose is to generate a hash code. The main purpose of hash code is to hash the object as a key input, it is easy
overriding equals in Java be sure to rewrite the Hashcode method
Original Author Blog address: Working with hashcode () and Equals () equals and Hashcode method
Equals, =, and hashcode in javaI. = explanation 1. simple background everything in Java is an object. When running a program, the storage location of each object has the following options: 1) Register: the fastest speed, the smallest capacity, in Java, the memory is completely transparent-it cannot be controlled or rec
The public boolean equals (Object obj) in object objects, and the method returns true for any non-null reference value x and Y, when and only if X and Y refer to the same object;Note: When this method is overridden, it is often necessary to override the Hashcode method to maintain the general contract of the Hashcode m
superclass is used, and the above notation causes always return false, which should be used with This.getclass ()! =obj.getclass () judgment. Third, hashcode () Java Dodumention recommends that each class that has the Equials override should override Hashcode. It is common to use Hashtable, HashMap, and hashset errors due to the absence of the override
First of all, to understand the role of hashcode, you must first know the collection in Java.
In general, the set in Java (Collection) has two classes, one is list, and the other is set. The elements in the former set are ordered, the elements can be duplicated, the latter elements are unordered, but the elements cannot be duplicated.
So here is a more serious
Preface
In Java, equals () and hashcode () functions work closely together. If you design one of them, you need to design another one. In most cases, these two functions do not need to be considered. Simply use their default design. However, in some cases, it is best to design these two functions to ensure the entireProgram. The most common is that when an obje
calculation commands.(2) Digital SignatureHash algorithms are also an important part of modern cryptographic systems. Because asymmetric algorithms are slow in operation,Therefore, in the Digital Signature Protocol, one-way hashing plays an important role. For the Hash value,It is also called "digital digest" for digital signature. in statistics, it can be considered as equivalent to digital signature for the file itself.This Protocol also has other advantages.(3) Authentication ProtocolThe fol
Equals in object is used to compare the equality of two objects, in general, when overriding this method, it is often necessary to also rewrite hashcode to maintain the general contract of the Hashcode method, which declares that the equality object must have an equal hash code. That is: if Obj1.
of the returned object (which can be viewed as an address ). Therefore, if the hashcode method is not rewritten, The hashcode of any object is not equal. Generally, the hashcode and equals methods need to be rewritten in the Collection class, because if you need to add an object to the Collection class (such as hashse
relation on objects;
* That's, for any non-null reference values {@code x} and
* {@code y}, this is returns {@code true} if and only
* If {@code x} and {@code y} refer to the same object
* ({@code x = = y} has the value {@code true}).
* * The It is generally necessary to override the {@code hashcode}
* Method whenever this and is overridden, and so as to maintain the
* General contract for the {@cod
over manually constructed equals () and Hashcode () methods (or Those Awful Monsters Eclipse would generate for your), but the guava versions is even Better.And a note about Hibernate:Be careful is about using the lazy collections in your equals (), hashcode () and toString () implementations. that'll fail miserably I
Only use to Hashtable, HashMap, HashSet, Linkedhashmap and so on to pay attention to hashcode, other places hashcode useless. (So understanding is not necessarily right)
Whether the two objects are equal or not requires hashcode () equality, and whether the statement below
In the Java collection, the rule that determ
Resolving the use of equals () and Hashcode () for Java objectsPrefaceIn the Java language, the use of equals () and hashcode () two functions are tightly matched, and if you design one of them yourself, you should design the othe
Reprint: http://www.oschina.net/question/82993_75533Hashcode () and Equals () are defined in the object class, which is the base class for all Java classes, so all Java classes inherit both methods.Hashcode is used primarily as set sets, and is a quick way to determine whether an object is "probably" equal to solve a large set of problems. For example, if a colle
();User3. Setuserid("111");User3. Settaskcontentid("123");To verify the symmetry of overriding equals system. out. println("User1.equals (user2):"+user1. Equals(User2));System. out. println("User2.equals (user1):"+user2. Equals(user1));Verify that the transitive system over
Excellent articles for reference:The fourth edition of Java programming ideas"Effective Java" second EditionThe map interface is the structure of the map table , maintaining the corresponding relationship between the key object and the value object, called the key-value pair .> Hashcode () and Equals ()
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