How is the hash code of an object generated in Java?

The hash code of a Java object is generated by the following formula: h = (h

#How is the hash code of an object generated in Java?

Hash code is an int value stored inside a Java object and is used to quickly identify and find the object. It is generated by the following formula:

hashCode = (h << 5) - h + x

where:

• h is the sum of the previous hash code left shifted by 5 bits and the original hash code The result (initial value is 0)
• x is the hash code of the object attribute value or pointer

For basic types, the hash code is stored directly in the object , such as:

int i = 10;
System.out.println(i.hashCode()); // 输出：10

For reference types, the hash code is generated based on the hash code list of its object, where:

hashCode = (hashcode1 * 31) + (hashcode2 * 31) + ... + (hashcodeN * 31)

where 31 is a prime number, called the "magic number", which helps To reduce hash collisions.

Practical case

Consider the following Person class:

class Person {
    private String name;
    private int age;
    
    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }
    
    @Override
    public int hashCode() {
        int hash = 0;
        if (name != null) {
            hash += name.hashCode() * 31;
        }
        hash += age * 31;
        return hash;
    }
}

This class covers hashCode() Method to generate a custom hash code, calculated based on the name and age attribute hash codes.

Person p1 = new Person("John", 25);
Person p2 = new Person("John", 25);

System.out.println(p1.hashCode() == p2.hashCode()); // 输出：true

In the above case, although p1 and p2 are different objects, the hash codes are the same since they have the same properties.

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