Java Basic Programming Help: Please make sure this program can compile and run.

Question

Java Basic Programming Help:

Please make sure this program can compile and run. Thanks!!

Write a program that reads each line in a file, reverses its lines, and writes them to another file.

For example, if the file input.txt contains the lines

Mary had a little lambIts fleece was white as snowAnd everywhere that Mary wentThe lamb was sure to go.

and you run

reverse input.txt output.txt

then output.txt contains

The lamb was sure to go.And everywhere that Mary wentIts fleece was white as snowMary had a little lamb

Explanation / Answer

ReadAnsWriteReverse.java

import java.io.File;
import java.io.FileNotFoundException;
import java.io.PrintStream;
import java.util.ArrayList;
import java.util.Scanner;

public class ReadAnsWriteReverse {

   public static void main(String[] args) throws FileNotFoundException {
       File file = new File("input.txt");
       if(file.exists()){
           ArrayList<String> list = new ArrayList<String>();
       Scanner scan = new Scanner(file);
       while(scan.hasNextLine()){
           list.add(scan.nextLine());
       }
       PrintStream ps = new PrintStream(new File("output.txt"));
       for(int i=list.size()-1; i>=0; i--){
           ps.println(list.get(i));
       }
       ps.flush();
       ps.close();
       System.out.println("File has been generated");
      
       }
       else{
           System.out.println("File does not exist.");
       }

   }

}

Output:

input.txt

Mary had a little lamb
Its fleece was white as snow
And everywhere that Mary went
The lamb was sure to go.

output.txt

The lamb was sure to go.
And everywhere that Mary went
Its fleece was white as snow
Mary had a little lamb

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