code: public static int javaDefaultHash(String str) {
  		int h = 0;
  		int off = 0;
  		int len = str.length();
  		for (int i = 0; i < len; i++) {
  			h = 31 * h + str.charAt(off++);
  		}
  		return h;
  	}
docs: JAVA自己带的算法
  
  @param str 字符串
  @return hash值