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：trueIn 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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