Check the class version
import java.io.DataInputStream; import java.io.FileInputStream; import java.io.IOException; public class Main { public static void main(String[] args) throws IOException { DataInputStream in = new DataInputStream(new FileInputStream("Main.class")); int start = in.readInt(); if (start != 0xcafebabe) { System.out.println("not valid"); } in.close(); System.out.println(in.readUnsignedShort()+"/"+in.readUnsignedShort()); } }