java - Object is altered during serialization? -

i trying serialize object, when deserialize set null. must missing something, please help. here serialize part:

public static void write(map<string, allat> m){   try {       fileoutputstream fileout = new fileoutputstream("savefile.txt");       objectoutputstream out = new objectoutputstream(fileout);       //m has correct parameters @ point       out.writeobject(m);       out.close();       fileout.close();   }   catch(ioexception i) {       i.printstacktrace();   }   system.out.println("success."); } 

here deserialize part:

public static map<string, allat> read(string path) {     map<string, allat> m;       try {           fileinputstream filein = new fileinputstream(path);           objectinputstream in = new objectinputstream(filein);           m = (map<string, allat>) in.readobject();           in.close();           filein.close();       }       catch(ioexception i) {           system.out.println("io exception");           i.printstacktrace();           return null;       }       catch(classnotfoundexception c) {           system.out.println("allat class not found");           c.printstacktrace();           return null;       }       return m; } 

after calling read method, in resulting object set null/0. "allat" class implement java.io.serializable. thank help!