File f=new File("*.txt")
long len=f.length();
byte [] buffer=new byte[len];

readFile.java:30: possible loss of precision
found   : long
required: int
     byte [] buffer2=new byte[len];

long len=f.length();
int lenF=(int) len;
byte [] buffer=new byte[lenF];

String source="this is just for FileWrite!";
char[] buffer=new char[source.length()];