PreAP Computer Science
The "Palindrome" Program
Text Lab 07
Practice/Perform Major Assignment
80, 90, 100 & 110 Point Versions
Assignment Purpose:
This program requires knowledge and manipulation of Java String objects.
Write a program that determines if an entered string is a Palindrome. True palindromes are strings
of characters that read the same backward as forward. This does mean all characters, including
spaces and punctuations. Examples of palindromes are:
MADAM, RACECAR, BOB, HANNAH, CIVIC, KAYAK, LEVEL, REVIVER
Text Lab 07 Student Version
Do not copy this file, which is provided.
// TextLab07st.java
// The "Palindrome" Program
// This is the student, starting version of Text Lab 07.
public class TextLab07st
{
public static void main (String args[])
{
System.out.println("\nTextLab07\n");
boolean finished = false;
do
{
System.out.print("Enter a string ===>> ");
String str = Expo.enterString();
System.out.println();
System.out.println("Entered String:
" + str);
System.out.println("Palindrome:
" + Palindrome.isPal(str));
System.out.println("Almost Palindrome: " + Palindrome.almostPal(str));
// used only for the 100 and 110 point versions
System.out.println("Least Palindrome:
" + Palindrome.leastPal(str));
// used only for the 110 point versions
System.out.println();
System.out.print("Do you wish to repeat this program [Y/N]?
char repeat = Expo.enterChar();
finished = (repeat != 'Y' && repeat != 'y');
System.out.println();
}
while (!finished);
===>>
}
}
Exposure Java 2012, PreAPCS Edition
Text Lab 07
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");
class Palindrome
{
public static boolean isPal(String s)
/*
* Precondition: s is an arbitrary String.
* Postcondition: The value of true is returned if s is a Palindrome,
*
false otherwise.
*/
{
return false;
}
public static String purge(String s)
/*
* Precondition: s is an arbitrary String.
* Postcondition: All non-letter characters are removed from s,
*
and this new "purged" String is returned.
*/
{
return s;
}
public static boolean almostPal(String s)
/*
* Precondition: s is an arbitrary String.
* Postcondition: After purging all non-letter characters from s,
*
the value of true is returned if the resulting
*
String is a Palindrome, false otherwise.
*/
{
return isPal(purge(s));
// Do not alter this method!
}
public static String leastPal(String s)
/*
* Precondition: s is an arbitrary String.
* Postcondition: A new String is returned which is created by adding the minimum
*
number of characters necessary to S to make it a Palindrome.
*/
{
return "";
}
}
Exposure Java 2012, PreAPCS Edition
Text Lab 07
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04-07-12
80 Point Version Specifics
The main thing this program needs to do is determine if an entered string is a Palindrome. To do
this, you must complete the isPal method. For this version, the isPal method is case-sensitive
meaning while madam and MADAM are palindromes, Madam is not.
You also are not concerned checking if the String is an Almost Palindrome and computing the Least
Palindrome. The program will generate some output for these, but it can be ignored.
80 Point Version Output
For the 80 and 90 Point Versions,
Almost Palindrome will always have
the same result as Palindrome and
Least Palindrome will always be blank.
Exposure Java 2012, PreAPCS Edition
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90 Point Version Specifics
The 90 point version is very similar to the 80 point version except now the isPal method is no longer
case sensitive. So madam and MADAM are still palindromes, but now Madam, mADAM, and
mADam are palindromes as well.
You also are not concerned with checking if the String is an Almost Palindrome or computing the
Least Palindrome. The program will generate some output for these, but it can be ignored.
90 Point Version Output
For the 80 and 90 Point Versions,
Almost Palindrome will always have
the same result as Palindrome and
Least Palindrome will always be blank.
Exposure Java 2012, PreAPCS Edition
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100 Point Version Specifics
The 100 point version requires everything from the 90 Point version and adds the ability to detect
Almost Palindromes. An Almost Palindrome is a sentence or phrase that becomes a Palindrome
when you remove any characters that are not letters. A few examples are below:
Madam I’m Adam.
A man, a plan, a canal, Panama
Not A Banana Baton!
You may have noticed that the almostPal method is already written for you. Before you get excited
about an easy 100, you need to understand how it is written. See the code below:
public static boolean almostPal(String s)
/*
* Precondition: s is an arbitrary String.
* Postcondition: After purging all non-letter characters from s,
*
the value of true is returned if the resulting String is a Palindrome,
*
false otherwise.
*/
{
return isPal(purge(s)); // Do not alter this method!
}
This is a very short method. If we look at the one statement in the method body and work our way
from the outside in, we see that first we send the value of s to the purge method, which will remove
all non-letter characters and then return the “purged” tring, which is then, in turn, sent to the isPal
method, which will determine if this is a Palindrome. If the purged string is a Palindrome, then the
original string is an Almost Palindrome.
If you look at the RaceCar example you be aware of 2 things. First, just like the 90 point version, this
version is not case sensitive. Second, for the purpose of this program a word or phrase that already
is a Palindrome, like RaceCar, will also be an Almost Palindrome.
You are not concerned with computing the Least Palindrome. It will simply be blank.
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100 Point Version Output
Since this 4th string has no letters whatsoever, it
is guaranteed to be an Almost Palindrome. When
all non-letter characters are removed, there is
nothing left, and an empty string is a Palindrome.
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110 Point Version Specifics
The 110 point version requires everything from the 100 point version and adds the ability to create
Least Palindromes. Consider the word Panama. It is not a Palindrome. It is also not an Almost
Palindrome. However, any string can be made into a Palindrome if you reverse the string and then
concatenate it to the end of the string. So in the case of Panama, the reverse is amanaP. If we
concatenate these we get PanamaamanaP which is a Palindrome, but it is not the Least Palindrome.
The reason it is not the Least Palindrome is we concatenated more characters than were necessary.
Simply by concatenating naP we get PanamanaP which not only is a Palindrome, it is the Least
Palindrome. By definition, this means if the entered string was already a Palindrome, like MADAM,
then is already is a Least Palindrome. In other words, the Least Palindrome of MADAM is MADAM.
110 Point Version Output
Since the first 2 strings
MADAM and RaceCar
are Palindromes, their
Least Palindromes will
be exactly the same.
Exposure Java 2012, PreAPCS Edition
Text Lab 07
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