Question

I need help with this code

This is what I need to do:

Implement the Stack Class with an ArrayList instead of an array, including the following
functions:
• empty
• push
• peek
• pop
• overrided toString( ) function which returns all of the stack’s contents
Things to note:
• You no longer need a size.
• You no longer need to define a constant DEFAULT_CAPACITY. Since ArrayLists
grow dynamically.
• Whenever possible, use ArrayList functions instead of the [ ] (index operator) to
implement your stack functions.
Then write a driver program to do palindrome check. A string is said to be a palindrome if it
does not change when the order of characters in the string is reversed. For example, MADAM,
45811854, and ABLE WAS I ERE I SAW ELBA are palindromes. In your driver program, you
are required to use the Stack class that you create in this lab to do the string processing. Your
program need to be able to read our provided text file, find which line is palindrome and which
line is not, and output all of palindromes line by line to a new file. Submit your work for credit.
Hint: You may consider to use a string(initialized as empty) and your Stack class in your program
that reads a line of sentence from the file, one character at a time, pushing only each letter
character/number character(not special sign, etc.) onto a stack as it is read and simultaneously
append it to the string. Then empty out the stack and put all of the letters/numbers to a second
string, which is used to hold the reversed string. Next compare the first string and the second
string to see if both are the same.

This is my code:

public class Test {
public static void main(String[] args) throws IOException {
Stack<Character> stack = new Stack<>();
BufferedReader br = new BufferedReader(new FileReader("C:\\Users\\kenae\\Downloads\\palindrome.txt"));
BufferedWriter bw = new BufferedWriter(new FileWriter("C:\\Users\\kenae\\Downloads\\palindrome.txt"));
String str;
while((str = br.readLine()) != null){
for(int i=0; i<str.length(); i++){
stack.push(str.charAt(i));
}
String revofstr="";
while (!stack.isEmpty()){
revofstr += stack.pop().toString();
}
if(str.equals(revofstr)){
bw.write("true");
bw.newLine();
}
else{
bw.write("false");
bw.newLine();
}
}

br.close();
bw.close();
}
}

import java.util.ArrayList;
import java.util.EmptyStackException;

public class Stack<E> {
private ArrayList<E> stack;

public Stack() {
stack = new ArrayList<E>();
}

public void push(E item) {
stack.add(item);
}

public E pop() {
if (!isEmpty())
return stack.remove(size()-1);
else
throw new EmptyStackException();
}

public boolean isEmpty() {
return (stack.size() == 0);
}

public E peek() {
if (!isEmpty())
return stack.get(size()-1);
else
throw new EmptyStackException();
}

public int size() {
return stack.size();
}

@Override
public String toString() {
return "ListStack [stack=" + stack.toString() + "]";

}
}

My problem is that this code is not outputing the file I want it to output. It is in my downloads folder and the file name is palindrome.txt What am I doing wrong? It is running but there is nothing being outputed

Answer 1

Your program implementation is correct.

But in java File, IO could not work for the same file at a time for reading as well as writing.

So you have to change the files you could use something like this

BufferedReader br = new BufferedReader(new FileReader("C:\\Users\\kenae\\Downloads\\palindrome.txt"));
BufferedWriter bw = new BufferedWriter(new FileWriter("C:\\Users\\kenae\\Downloads\\palindrome_output.txt"));

It would work if you change the file names.

Please find the output below: