这个程序是替换word编译器在bluej中没有引发错误但仍未执行，并且没有显示输出窗口

class replace
{
    public static void main(String sent,String fword,String rword)
    {
        int wlen=fword.length();
        int pos,n;
        n=0;
        String prev,next;
        do
        {
            pos=sent.indexOf(fword);
            if(pos!=-1)
            {
                n=pos+wlen;
                prev=sent.substring(0,pos);
                next=sent.substring(n);
                sent=prev+rword+next;

            }//end of if 
        }while(pos !=1);
        System.out.println("modified sentence:"+ sent);
    }//end of main
}//endof class
class replace
{
    public static void main(Str