Question

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.

Please do this question in Java. I really don't understand how to incorporate the function within a file when reading it line by line and outputting it to another file.

Answer 1

Solution:

ListStack.java

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

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

    public ListStack() {
        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() + "]";

    }
}

Test.java

import java.io.*;

public class Test {
    public static void main(String[] args) throws IOException {
        ListStack<Character> stack = new ListStack<>();
        BufferedReader br = new BufferedReader(new FileReader("C:\\Users\\input.txt"));
        BufferedWriter bw = new BufferedWriter(new FileWriter("C:\\Users\\output.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();
    }
}

input.txt

MADAM
45811854
ABLE WAS I ERE I SAW ELBA
MISI
GOIOG

output.txt

true
true
true
false
true

====================================================================================

====================================================================================

NOTE : you can print anything instead of true/false in output file. If you want to print palindrome string then you just need to change the if and else case into main() function as below

if(str.equals(revofstr)){
    bw.write(str+" is palindrome");
    bw.newLine();
}
else{
    bw.write(str+" is not palindrome");
    bw.newLine();
}

then your output.txt will be :

MADAM is palindrome
45811854 is palindrome
ABLE WAS I ERE I SAW ELBA is palindrome
MISI is not palindrome
GOIOG is palindrome