String hashcode()

String hashcode()代码段

  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;
    }

    @Test
    public void test() {

        //【对应Unicode字符集编码值a97;b98;c99】
        String s = new String("abc"); 

        //验证方式1、公式h=31 * h + val[i];
        //h=31*0+97=97
        //h=31*(31*0+97)+98=31*97+98=3105
        //h=31*[31*(31*0+97)+98]=31*3105+99=96354

        System.out.println(96354 == s.hashCode());//true

        //验证方式2：hashCode()计算公式：s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1]
        //h=97*31^(3-1)+98*31(2-1)+99*31(1-1)=96354
    }