Make sure the file resides in the project folder if you're referencing it via a relative path. If not, use the absolute path to the file with the file extension.
java.io.FileNotFoundException: registrar.ser (The system cannot find the file sp
ecified) at java.io.FileInputStream.open(Native Method) at java.io.FileInputStream.(Unknown Source) at java.io.FileInputStream.(Unknown Source) at undefined.StudentRegisterApp.main(StudentRegisterApp.java:10)