How to Update a File in Java?
- Java
// Java program to update in the file "friendsContact.txt"
// and change the number of an old contact
import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.lang.NumberFormatException;
class UpdateFriend {
public static void main(String data[])
{
try {
// Get the name of the contact to be updated
// from the Command line argument
String newName = data[ 0 ];
// Get the number to be updated
// from the Command line argument
long newNumber = Long.parseLong(data[ 1 ]);
String nameNumberString;
String name;
long number;
int index;
// Using file pointer creating the file.
File file = new File( "friendsContact.txt" );
if (!file.exists()) {
// Create a new file if not exists.
file.createNewFile();
}
// Opening file in reading and write mode.
RandomAccessFile raf
= new RandomAccessFile(file, "rw" );
boolean found = false ;
// Checking whether the name
// of contact already exists.
// getFilePointer() give the current offset
// value from start of the file.
while (raf.getFilePointer() < raf.length()) {
// reading line from the file.
nameNumberString = raf.readLine();
// splitting the string to get name and
// number
String[] lineSplit
= nameNumberString.split( "!" );
// separating name and number.
name = lineSplit[ 0 ];
number = Long.parseLong(lineSplit[ 1 ]);
// if condition to find existence of record.
if (name == newName
|| number == newNumber) {
found = true ;
break ;
}
}
// Update the contact if record exists.
if (found == true ) {
// Creating a temporary file
// with file pointer as tmpFile.
File tmpFile = new File( "temp.txt" );
// Opening this temporary file
// in ReadWrite Mode
RandomAccessFile tmpraf
= new RandomAccessFile(tmpFile, "rw" );
// Set file pointer to start
raf.seek( 0 );
// Traversing the friendsContact.txt file
while (raf.getFilePointer()
< raf.length()) {
// Reading the contact from the file
nameNumberString = raf.readLine();
index = nameNumberString.indexOf( '!' );
name = nameNumberString.substring(
0 , index);
// Check if the fetched contact
// is the one to be updated
if (name.equals(inputName)) {
// Update the number of this contact
nameNumberString
= name + "!"
+ String.valueOf(newNumber);
}
// Add this contact in the temporary
// file
tmpraf.writeBytes(nameNumberString);
// Add the line separator in the
// temporary file
tmpraf.writeBytes(
System.lineSeparator());
}
// The contact has been updated now
// So copy the updated content from
// the temporary file to original file.
// Set both files pointers to start
raf.seek( 0 );
tmpraf.seek( 0 );
// Copy the contents from
// the temporary file to original file.
while (tmpraf.getFilePointer()
< tmpraf.length()) {
raf.writeBytes(tmpraf.readLine());
raf.writeBytes(System.lineSeparator());
}
// Set the length of the original file
// to that of temporary.
raf.setLength(tmpraf.length());
// Closing the resources.
tmpraf.close();
raf.close();
// Deleting the temporary file
tmpFile.delete();
System.out.println( " Friend updated. " );
}
// The contact to be updated
// could not be found
else {
// Closing the resources.
raf.close();
// Print the message
System.out.println( " Input name"
+ " does not exists. " );
}
}
catch (IOException ioe) {
System.out.println(ioe);
}
catch (NumberFormatException nef) {
System.out.println(nef);
}
}
}
Output:
Compiling and updating the contact in the file:
javac UpdateFriend.java java UpdateFriend abc 1234567890 Friend updated. java UpdateFriend tqr Input name does not exists.
How to Delete a File in Java?
- Java
// Java program to delete a contact
// from the file "friendsContact.txt"
import java.io.File;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.lang.NumberFormatException;
class DeleteFriend {
public static void main(String data[])
{
try {
// Get the name of the contact to be updated
// from the Command line argument
String newName = data[ 0 ];
String nameNumberString;
String name;
long number;
int index;
// Using file pointer creating the file.
File file = new File( "friendsContact.txt" );
if (!file.exists()) {
// Create a new file if not exists.
file.createNewFile();
}
// Opening file in reading and write mode.
RandomAccessFile raf
= new RandomAccessFile(file, "rw" );
boolean found = false ;
// Checking whether the name of contact exists.
// getFilePointer() give the current offset
// value from start of the file.
while (raf.getFilePointer() < raf.length()) {
// reading line from the file.
nameNumberString = raf.readLine();
// splitting the string to get name and
// number
String[] lineSplit
= nameNumberString.split( "!" );
// separating name and number.
name = lineSplit[ 0 ];
number = Long.parseLong(lineSplit[ 1 ]);
// if condition to find existence of record.
if (name == newName) {
found = true ;
break ;
}
}
// Delete the contact if record exists.
if (found == true ) {
// Creating a temporary file
// with file pointer as tmpFile.
File tmpFile = new File( "temp.txt" );
// Opening this temporary file
// in ReadWrite Mode
RandomAccessFile tmpraf
= new RandomAccessFile(tmpFile, "rw" );
// Set file pointer to start
raf.seek( 0 );
// Traversing the friendsContact.txt file
while (raf.getFilePointer()
< raf.length()) {
// Reading the contact from the file
nameNumberString = raf.readLine();
index = nameNumberString.indexOf( '!' );
name = nameNumberString.substring(
0 , index);
// Check if the fetched contact
// is the one to be deleted
if (name.equals(inputName)) {
// Skip inserting this contact
// into the temporary file
continue ;
}
// Add this contact in the temporary
// file
tmpraf.writeBytes(nameNumberString);
// Add the line separator in the
// temporary file
tmpraf.writeBytes(
System.lineSeparator());
}
// The contact has been deleted now
// So copy the updated content from
// the temporary file to original file.
// Set both files pointers to start
raf.seek( 0 );
tmpraf.seek( 0 );
// Copy the contents from
// the temporary file to original file.
while (tmpraf.getFilePointer()
< tmpraf.length()) {
raf.writeBytes(tmpraf.readLine());
raf.writeBytes(System.lineSeparator());
}
// Set the length of the original file
// to that of temporary.
raf.setLength(tmpraf.length());
// Closing the resources.
tmpraf.close();
raf.close();
// Deleting the temporary file
tmpFile.delete();
System.out.println( " Friend deleted. " );
}
// The contact to be deleted
// could not be found
else {
// Closing the resources.
raf.close();
// Print the message
System.out.println( " Input name"
+ " does not exists. " );
}
}
catch (IOException ioe) {
System.out.println(ioe);
}
}
}
Output:
Compiling and deleting the contact in the file:
javac DeleteFriend.java java DeleteFriend pqr Friend deleted. java DeleteFriend tqr Input name does not exists.