What is the Reason Behind Boolean.hashCode() Returning 1231 and 1237?

What is the reason behind Boolean.hashCode() returning 1231 and 1237?

public int hashCode() {
    return value ? 1231 : 1237;
}

The hashCode method for the Boolean class in Java returns 1231 if the value is true and 1237 if the value is false. This design choice is due to ensuring distinct and non-zero hash codes for the two Boolean values, which is crucial for effective hashing algorithms.

public int hashCode() {
    return value ? 1231 : 1237;
} // Returns unique hash codes for true and false

Causes

• Facilitates efficient storage and retrieval in hash-based collections, such as HashMap or HashSet.
• The two distinct integers (1231 for true and 1237 for false) are carefully chosen primes to minimize collisions.
• Ensures that the hashCode method adheres to the requirements of consistency and performance, which are critical in Java's Collection framework.

Solutions

• When implementing hashCode in custom classes, consider using distinct prime numbers to minimize collisions.
• Follow consistent practices in hashCode and equals method implementations to avoid unexpected behavior in collections.

Mistake: Not overriding the hashCode method when equals is overridden in custom classes.

Solution: Always ensure that if you override equals, you also override hashCode to maintain the contract between them.

Mistake: Using arbitrary numbers for hash codes without considering their distribution.

Solution: Use prime numbers in hash code functions to achieve better distribution and reduce collisions.