java String 怎么看里面有几个指定字符

public class Main {
 
 
    public static void main(String[] args) {
        RrdDef rrdDef;
        RrdDb rrdDb;
        String str = "divabcdivbbdivcdivdde",
               des = "div";
         
        int cnt = 0;
        int offset = 0;
        while((offset = str.indexOf(des, offset)) != -1){
            offset = offset + des.length();
            cnt++;
        }
        System.out.println(cnt);
    }
}