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String 类 的hashCode方法

s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1] 

/**     * Returns a hash code for this string. The hash code for a     * {@code String} object is computed as     * 
   
    
     * s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1]     * 
   
     * using {@code int} arithmetic, where {@code s[i]} is the     * ith character of the string, {@code n} is the length of     * the string, and {@code ^} indicates exponentiation.     * (The hash value of the empty string is zero.)     *     * @return  a hash code value for this object.     */    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;    }

来个例子

/** * Created by tiantao on 2018/6/13. */public class StringTest{    public static void main(String[] args) {        //49        System.out.println("1".hashCode());                //49 * 31 + 49 = 1568        System.out.println("11".hashCode());                //49 * 31 * 31 + 49 * 31  + 49 = 48657        System.out.println("111".hashCode());                //49 * 31 * 31 + 50 * 31  + 51 = 48690        System.out.println("123".hashCode());    }}

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