字节流字节数组

 File f = new File("src/abc.txt");

        //  project structure/Modules/ Use modules compile output path选中即显示相对路径
        InputStream io = new FileInputStream(f);
        byte[] flush= new byte[4];
        int len = -1;
        //io.read()末尾返回-1，其他返回相应int
        while((len = io.read(flush))!=-1){
            //len不可少 否则会在byte[]后附加
            System.out.print(new String(flush,0,len)+" ");
        }
        io.close();