Why Doesn't Java's String Class Cache a HashCode of Zero?

Why doesn't Java's String class cache a hashCode of zero?

public class Main {
    static void test(String s) {
        long start = System.currentTimeMillis();
        for (int i = 0; i < 10000000; i++) {
            s.hashCode();
        }
        System.out.format("Took %d ms.%n", System.currentTimeMillis() - start);
    }
    public static void main(String[] args) {
        String z = "Allocator redistricts; strict allocator redistricts strictly.";
        test(z);
        test(z.toUpperCase());
    }
}

In Java, the String class only caches non-zero hash codes to optimize performance. When the hashCode is zero, caching it could lead to unnecessary space and cost for very rare cases.

// Implementation of a simple caching example for custom String class
class CachedString {
    private final String value;
    private int cachedHashCode;
    private boolean isCached;

    public CachedString(String value) {
        this.value = value;
        this.isCached = false;
    }

    public int hashCode() {
        if (!isCached) {
            cachedHashCode = value.hashCode();
            isCached = true;
        }
        return cachedHashCode;
    }
}

Causes

• The default hash code implementation produces zero for certain string values due to the nature of the hash function.
• Caching a hash code of zero doesn't significantly optimize performance since the cost of recalculating the hash code may not substantially impact most applications.

Solutions

• Instead of relying solely on hashCode caching, optimize string usage in your application logic where possible.
• Use alternative data structures like HashMap where the actual computation of hash is lightweight, rather than focusing on caching .

Mistake: Assuming that caching is universally beneficial without analyzing real performance implications.

Solution: Evaluate performance differences in context. Test before and after caching to measure actual benefits.

Mistake: Overusing custom caching mechanisms leading to increased complexity.

Solution: Keep caching logic simple and maintainable, considering when to cache based on actual usage patterns.