Many of the Java programmers know what 'Hashcode' means, but don't really know how exactly it is calculated and why 31 is used to calculate the hashcode. Below is the code snippet from Java 1.6, which calculates the hashcode for a string: publicinthashCode() {inth =hash;if(h == 0)...
首先不要把任意字符对应到数字0,比如假如把a对应到数字0,那么将不能只从Hash结果上区分ab和b(虽然可以额外判断字符串长度,但不把任意字符对应到数字0更加省事且没有任何副作用),因为00,0000,000000都对应数值0,失去了长度信息 对于字符串而言我们可以把字符串看成一个26进制数 如果包含其他特殊符号,可看成|S|进...
1 如果两个对象相等(equals),那么必须拥有相同的哈希码(hash code) 2 即使两个对象有相同的哈希值(hash code),他们不一定相等(equals). 首先看一下Object中这两个方法的源码 /** * Returns a hash code value for the object. This method is * supported for the benefit of hashtables such as those ...
Java 生成字符串的Hash值: /*** A hashing method that changes a string (like a URL) into a hash suitable for using as a * disk filename.*/publicstaticString hashKeyForDisk(String key) { String cacheKey;try{finalMessageDigest mDigest = MessageDigest.getInstance("MD5"); mDigest.update(key....
① String是引用类型,内部并不存储字符串本身,这点我们可以从原码看出,其内部分为两部分 分别为 value 【存储数组】和 hash【默认为0】 public static void main(String[] args) {// s1 和 s2引用的是不同对象 s1 和 s3引用的是同一对象String s1 = new String("hello");String s2 = new String("world...
Reddit文章:https://www.reddit.com/r/coding/comments/967hci/stringhashcode_is_not_even_a_little_unique/ 相关测试:https://vanilla-java.github.io/2018/07/26/Stringhash-Code-is-not-even-a-little-unique.html 生日问题:https://en.wikipedia.org/wiki/Birthday_problem ...
hash 的计算方法是: s[i] 是 string 的第 i+1 个字符,s[0] 表示第 1 个字符,n 是 String 的长度。s[0]*31^(n-1) 表示 31 的 n-1 次方再乘以第一个字符的值。 为什么是 31,可以参考 stackoverflow 相关问题 Why does Java's hashCode() in String use 31 as a multiplier?
public final class String implements java.io.Serializable, Comparable<String>, CharSequence, Constable, ConstantDesc { @Stable private final byte[] value; //字符串实际上就存储在这个用final修饰的byte数组中 private final byte coder; /** Cache the hash code for the string */ ...
The hashCode() method returns the hash code of a string.The hash code for a String object is computed like this:s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1] where s[i] is the ith character of the string, n is the length of the string, and ^ indicates ...