strbuf.delete(2, strbuf.length()); //这句话是什么意思

Question

public void addCards(){
        String[] color ={"黑桃","红桃","梅花","方片"};
        String[] num = {"2","3","4","5","6","7","8","9","10","J","Q","K","A"};
        int c =0;
        System.out.println("------------创建扑克牌-------------");
        for(int i = 0; i < 4; i++)
        {           
             StringBuffer strbuf=new StringBuffer();
             strbuf .append(color[i]);
             for(int  j = 0; j < 13; j++){
                strbuf.insert(2, num[j]);
                Cards card = new Cards();
                card.name = strbuf.toString();
                cardsToSelect.add(c, card);
                c++;
                strbuf.delete(2, strbuf.length());
//这句话是什么意思
            }
         }
        System.out.println("----------扑克牌创建成功！---------------");

        for (Cards card : cardsToSelect) {
            System.out.print(card.name+",");

        }
            System.out.println();
     }