1. Accessing Files in Java
Lesson 5

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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); }

9. 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

10. 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

11. 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

12. Results of the File Read
Line printed by the printRec method