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This article focuses on "what is the purpose of rewriting the hashCode () method in Java". Interested friends may wish to take a look. The method introduced in this paper is simple, fast and practical. Let's let the editor take you to learn "what is the purpose of rewriting the hashCode () method in Java?"

1. Why override the equals () method?

Because the equals () method in object compares whether the reference address of the object is equal, when you need to determine whether the content in the object is equal, you need to override the equals () method.

Which classes in 2.Java override the equals () method?

Most of the classes in java override the equals () method, and most of the classes that are not overridden are self-defined classes, such as defining a student class, which does not override the equals () method.

What is the function of the 3.hashcode () method?

The hashCode method in Java maps the information related to the object (such as the storage address of the object, the fields of the object, etc.) into a numeric value, which is called the hash value, according to certain rules. It is mainly for HashSet and Map collection types. For example, when we add new elements to the HashSet collection, since elements are not allowed to repeat in the set collection, we need to determine whether the inserted element exists before inserting the new element. First, we get the hashcode value of the object according to the hashCode () method. If the value does not exist in the collection, you can insert it directly. If it already exists, it needs to be compared again through equals (), which can improve efficiency.

4. Why override the equals () method and override the hashcode () method at the same time?

Overriding the equals () method also overrides the hashcode () method to ensure that when two objects are compared to be equal through the equals () method, their hashCode values must be equal.

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