Reversing word with Stack

Question

I am not sure why this is giving me an error. I am in the method pop and i want to return the value stored at the position top. Though it says they are incompatible types. I do not see why it should be a problem as I only want the character to be printed out at the position. This is part of a bigger program just so you know and will be getting the word from a different class.

public class Stack
{
private int maxSize;
private String[] stackArray;
private int top;
/**
 * Constructor for objects of class Stack
 */
    public Stack(int a)
    {
      maxSize = a;
      stackArray = new String [maxSize];
       top = -1;
    }

   public void push(String j)
   {
     top++;
     stackArray[top] = j;
   }  

   public char pop()
   {
     return stackArray[top--];//Error is here
   }

}

Answer 1

stackArray is a string array and the return type of your method is char .

---

Reversing word with Stack

If you want to reverse a word with your Stack object, consider using a char array and not a String array .

class Stack
{
private int maxSize;
private char[] stackArray;
private int top;
/**
 * Constructor for objects of class Stack
 */
    public Stack(int a)
    {
      maxSize = a;
      stackArray = new char [maxSize];
       top = -1;
    }

   public void push(char j)
   {
     top++;
     stackArray[top] = j;
   }  

   public char pop()
   {
     return stackArray[top--];
   }

   public int getSize(){
     return maxSize;
   }
}

And the following test case :

        String s = "test";
        Stack st = new Stack(s.length());

        for(char c : s.toCharArray())
            st.push(c);

        for(int i = 0; i <st.getSize();i++)
            System.out.print(st.pop());

Output :

tset

Answer 2

You're pushing String s onto your array (which is an array of String s), and trying to pop a char . Change your method to

public String pop() {
    return stackArray[top--];
}

Answer 3

Your signature says you are returning a char, but you are returning a String.

change

public char pop()

to

public String pop()

Answer 4

You have two choices

• In the pop method, return the char you want from the top string
• where you call pop , get the char from the String that was returned from pop .

The second choice is probably the better of the two as one would expect pop to return whatever type is on the stack.