阅读下段代码 import java.io.*;public class Example{ public static void main(String[] args) throws Exception { FileInputStream fis = new FileInputStream("file.txt"); FileOutputStream fos = new FileOutputStream("copy_file.txt"); int ch = 0; while((ch =fis.read())!=-1){ fos.write(ch); } fos._______; fis.close(); }}请说出下划线上,填写的方法名称( )