Prerequisite : PrintWriter , BufferedReader
Given two files input.txt and delete.txt. Our Task is to perform file extraction(Input-Delete) and save the output in file say output.txt
Example :
Naive Algorithm :
1. Create PrintWriter object for output.txt
2. Open BufferedReader for input.txt
3. Run a loop for each line of input.txt
3.1 flag = false
3.2 Open BufferedReader for delete.txt
3.3 Run a loop for each line of delete.txt
-> If line of delete.txt is equal to current line of input.txt
-> flag = true
-> break loop
4. Check flag, if false
-> write current line of input.txt to output.txt
5. Flush PrintWriter stream and close resources.
To successfully run the below program input.txt and delete.txt must exits in same folder OR provide full path for them.
// Java program to perform file// operation output = input-delete import java.io.*; public class FileOperation{ public static void main(String[] args) throws IOException { // PrintWriter object for output.txt PrintWriter pw = new PrintWriter("output.txt"); // BufferedReader object for input.txt BufferedReader br1 = new BufferedReader(new FileReader("input.txt")); String line1 = br1.readLine(); // loop for each line of input.txt while(line1 != null) { boolean flag = false; // BufferedReader object for delete.txt BufferedReader br2 = new BufferedReader(new FileReader("delete.txt")); String line2 = br2.readLine(); // loop for each line of delete.txt while(line2 != null) { if(line1.equals(line2)) { flag = true; break; } line2 = br2.readLine(); } // if flag = false // write line of input.txt to output.txt if(!flag) pw.println(line1); line1 = br1.readLine(); } pw.flush(); // closing resources br1.close(); pw.close(); System.out.println("File operation performed successfully"); }} |
Output:
File operation performed successfully
Note : If output.txt exist in cwd(current working directory) then it will be overwritten by above program otherwise new file will be created.
A better solution is to use HashSet to store each line of delete.txt and then while looping through lines of input.txt ,check if it is in hashset. If not present, write that line into output.txt.
To successfully run the below program input.txt and delete.txt must exits in same folder OR provide full path for them.
// Efficient Java program to perform file// operation output = input-delete import java.io.*;import java.util.HashSet; public class FileOperation{ public static void main(String[] args) throws IOException { // PrintWriter object for output.txt PrintWriter pw = new PrintWriter("output.txt"); // BufferedReader object for delete.txt BufferedReader br2 = new BufferedReader(new FileReader("delete.txt")); String line2 = br2.readLine(); // hashset for storing lines of delete.txt HashSet<String> hs = new HashSet<String>(); // loop for each line of delete.txt while(line2 != null) { hs.add(line2); line2 = br2.readLine(); } // BufferedReader object for input.txt BufferedReader br1 = new BufferedReader(new FileReader("input.txt")); String line1 = br1.readLine(); // loop for each line of input.txt while(line1 != null) { // if line is not present in delete.txt // write it to output.txt if(!hs.contains(line1)) pw.println(line1); line1 = br1.readLine(); } pw.flush(); // closing resources br1.close(); br2.close(); pw.close(); System.out.println("File operation performed successfully"); }} |
Output:
File operation performed successfully
Note : If output.txt exist in cwd(current working directory) then it will be overwritten by above program otherwise new file will be created.
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