在【1】-【5】处填上适当的代码,使程序能正常运行 importjava.io.*; //将a.txt的内容复制到b.txt publicclassDemo{ publicstaticvoidmain(String[]args)throwsIOException{ 【1】=newBufferedReader(newFileReader("a.txt")); BufferedWriterbw=newBufferedWriter(【2】); Strings1=null; 【3】{ while((s1=【4】.readLine())!=null){ 【5】.write(s1); System.out.print(s1); } }catch(IOExceptione){ }finally{bw.close();br.close();} } }