Accessing Files in Java Lesson 5

Reading Text from a File Use FileInputStream and DataInputStream File types are “wrapped” FileInputStream in = new FileInputStream ("nameNumber.txt"); DataInputStream s = new DataInputStream (in); Command then used is stringVal = s.readLine() Note Source code of readStrings.java

Program Features Note the specification of exception handling public static void main(String args[ ]) throws IOException This requires a try block and a catch block catch (IOException ioe) { } Note contents of input file and resulting output

Declaring a Class Declared in a separate file – nameRec.java Methods declared, implemented within the class declaration Note use of public specifiers (some things can also be private) For objects of this class to be saved as binary file records, implements Serializable must be declared Class will be used by another program

Must specify this for saving objects of this type to a file Declaring a Class public class nameRec extends Object implements Serializable{   public String name; public double dNum; public int iNum; public void nameRec() { name = ""; dNum=0.0; iNum = 0; } public String getName() { return name; } Must specify this for saving objects of this type to a file Data attributes Constructor

Declaring a Class public void setRec (String n, double d, int i) { name = n; dNum = d; iNum = i; } public void nameRec(String n, double d, int i) setRec (n, d, i);   public void printRec () System.out.println ("Record : "+name+" "+dNum+" "+iNum); Another constructor

Creating a Binary Data File ReadNameNum.java nameRec object instantiated Open the text file to be read FileInputStream wrapped in DataInputStream Open the file for nameRec object output FileOutputStream wrapped in ObjectOutputStream

Creating a Binary Data File Prime the pump Check for end of file Process the record Cast object as it is written Try to read the next record nRec = readRecord (in); while (nRec.getName() != null) { nRec.printRec(); s.writeObject ((nameRec) nRec); nRec = readRecord(in); }

Manipulating Text to Load the Object public static nameRec readRecord (DataInputStream in) throws IOException { String name = null, iString = null, dString = null; name = in.readLine(); iString = in.readLine(); dString = in.readLine() ; nameRec temp = new nameRec (); if (dString == null) return temp; // no more records Double d = Double.valueOf(dString); Integer i = Integer.valueOf(iString); int ii = i.intValue(); double dd = d.doubleValue();   temp.setRec (name, dd,ii); return temp; } Reading the data Change strings to Integer and Double “wrapped” objects Call nameRec set method

Reading Objects from a File readNameRec.java Note import nameRec; The wrapping of the FileInputStream in the ObjectInputStream file Instantiation of the nameRec object throw, try, and catch specifications

Reading Objects from a File public class readNameRec { public static void main (String[] args) throws IOException, ClassNotFoundException { ObjectInputStream s = (new ObjectInputStream (new FileInputStream ("nameNum.dat"))); nameRec nRec = new nameRec(); try { while ((nRec = (nameRec)s.readObject()) != null) nRec.printRec(); } catch (IOException ioe) { } catch (ClassNotFoundException cnfe) { } Error handling specifications Do the I/O in the condition

Results of the File Read Line printed by the printRec method