为什么用isflag就会报错直接在whliel里面写True就不会求大神回复！！

public static char readChargender(){
     char c;
      boolean isflag=true;
      while(isflag){
          String str=readKeyboard(1,false);
           c=str.charAt(0);
          if(c=='男'||c=='女'){
              return c;
          }else {
              System.out.println("输入错误请重新输入");
          }
      }
     }