public int hashCode() {
        int h = hash;
        if (h == 0 && value.length > 0) {
            char val[] = value;

            for (int i = 0; i < value.length; i++) {
                h = 31 * h + val[i];
            }
            hash = h;
        }
        return h;
    }

Why does Java‘s hashCode() in String use 31 as a multiplier?

Consistency of hashCode() on a Java string

java：String类hashCode()的实现

原文：http://my.oschina.net/letiantian/blog/339015