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help! trouble with pop method

Russ Russ

Joined: Oct 21, 2002
Posts: 4
My applet is supposed to detect palindromes (words that are spelled the same forwards or backwords, ie "radar").
GUI is named WordGUI.
Stack class is named WordStack.
I am trying to use the pop() with stacks. I was able to use the push() without problems. Basically, I'm accepting user input from a textfield in my WordGUI class and pushing each char onto a stack array named data. Then I need to pop the chars out of the data array into a new stack array called popped. I then need to compare the contents of the 2 arrays to see if they are equal. If they are - we have detected a palindrome. Mission accomplished.
So... what am I doing wrong with my pop method? I think there's also a problem with my for loop that uses pop. Any ideas? Thank you.
package assign4;
import java.awt.*;
import java.awt.event.*;
import java.applet.*;
public class WordGUI extends Applet implements ActionListener{
WordStack myStack = new WordStack();
private Button testButton;
private TextField wordField;
private boolean isPalindrome = false;
char popOutput;
public void init(){
wordField = new TextField(20);
testButton = new Button("Test for palindromes");
public void paint (Graphics g){
g.drawString("Enter a word in the textField above and click", 25, 100);
g.drawString("the button to check if the word is a palindrome", 25, 115);
myStack.display(g, 150);//used for testing purposes here
g.drawString("Is a palindrome!", 25, 75);
g.drawString("Is not a palindrome", 25, 75);
public void actionPerformed(ActionEvent event){
if(event.getSource() == testButton){
String userInput = wordField.getText();
isPalindrome = myStack.evaluate(userInput);
}//class WordGUI
package assign4;
import java.awt.*;
import java.awt.event.*;
import java.applet.*;
public class WordStack implements Cloneable{
private char[] data;
private char[] popped;
private int manyItems;
private boolean isPalindrome = false;
public WordStack(){
final int initialCapacity = 10;
manyItems = 0;
data = new char[initialCapacity];
popped = new char[initialCapacity];
}//generic constructor
public WordStack(int initialCapacity){
if(initialCapacity < 0){
throw new IllegalArgumentException
("initialCapacity too small: " + initialCapacity);
manyItems = 0;
data = new char[initialCapacity];
popped = new char[initialCapacity];
public int getCapacity(){
return data.length;
public boolean isEmpty(){
return (manyItems == 0);
public char pop(){
if(manyItems == 0){
//throw new EmptyStackException();
return data[--manyItems];

public boolean evaluate(String userInput){
for(int i = 0; i < userInput.length(); i++){
for(int i = 0; i < userInput.length(); i++){
popped[0] = pop();
return true;
return false;
public void push(char item){
if(manyItems == data.length){
ensureCapacity(manyItems * 2 + 1);
data[manyItems] = item;
public void ensureCapacity(int minimumCapacity){
char biggerArray[];
if(data.length < minimumCapacity){
biggerArray = new char[minimumCapacity];
System.arraycopy(data, 0, biggerArray, 0, manyItems);
data = biggerArray;

public void display(Graphics g, int yLoc){//being used for testing purposes here
for(int i = 0; i < data.length; i++){
g.drawString("" + data[i] + popped[i], 25, yLoc);
yLoc += 15;
public void trimToSize(){
char trimmedArray[];
if(data.length != manyItems){
trimmedArray = new char[manyItems];
System.arraycopy(data, 0, trimmedArray, 0, manyItems);
data = trimmedArray;
}//class WordStack
Thomas Paul
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Joined: May 05, 2000
Posts: 13974
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