APCS A FRQ 2015 Question 2

Goal of the FRQ

This free-response question asks you to write a complete Java class called HiddenWord.

The class must:

Store the hidden word.
Have a constructor that receives the hidden word.
Have a method called getHint.
Compare the hidden word with the guess one letter at a time.
Return a hint using letters, plus signs, and stars.

Hint Rules

If the guess letter is...	The hint should show...
In the same position as the hidden word	The matching letter
In the hidden word, but in a different position	`+`
Not in the hidden word	`*`

Step 1: Create the Class

The problem says to write the complete HiddenWord class.

public class HiddenWord
{

}

Step 2: Add an Instance Variable

The class needs to remember the hidden word.

private String word;

This variable stores the hidden word that is passed into the constructor.

Step 3: Write the Constructor

The constructor receives the hidden word and stores it in the instance variable.

public HiddenWord(String h)
{
    word = h;
}

Example:

HiddenWord puzzle = new HiddenWord("HARPS");

Now the instance variable word stores "HARPS".

Step 4: Understand the getHint Method

The getHint method receives a guess and returns a hint.

puzzle.getHint("HEART");

The hidden word is:

HARPS

The guess is:

HEART

Now compare each letter by position.

Index	Hidden Word	Guess	Result
0	H	H	Same position, use `H`
1	A	E	E is not in HARPS, use `*`
2	R	A	A is in HARPS, but different position, use `+`
3	P	R	R is in HARPS, but different position, use `+`
4	S	T	T is not in HARPS, use `*`

The final hint is:

H*++*

Step 5: Use a Loop

Since every letter must be checked, use a for loop.

for (int i = 0; i < guess.length(); i++)
{

}

This loop checks each character in the guess from left to right.

Step 6: Get Each Letter

Use substring to get one character at a time.

String letter = guess.substring(i, i + 1);

Example:

If guess is "HEART", then:

guess.substring(0, 1)

returns:

"H"

Step 7: Check for Exact Match First

The most important rule is checking whether the guessed letter is in the exact same position as the hidden word.

if (letter.equals(word.substring(i, i + 1)))
{
    hint += letter;
}

This checks whether the guessed letter matches the hidden word at the same index.

Example:

Hidden: H A R P S
Guess:  H E A R T
Index:  0

The H matches exactly, so the hint gets H.

Step 8: Check if the Letter Exists Somewhere Else

If the letter is not an exact match, check if it appears anywhere in the hidden word.

Use indexOf.

word.indexOf(letter)

If the letter is found, indexOf returns its position. If the letter is not found, indexOf returns -1.

else if (word.indexOf(letter) != -1)
{
    hint += "+";
}

Example:

If the hidden word is "HARPS" and the guess letter is "A", then A is in the hidden word.

Since it is not in the correct position, add +.

Step 9: If the Letter Is Not Found

If the letter is not an exact match and is not in the hidden word, add *.

else
{
    hint += "*";
}

Complete Solution

public class HiddenWord
{
    private String word;

    public HiddenWord(String h)
    {
        word = h;
    }

    public String getHint(String guess)
    {
        String hint = "";

        for (int i = 0; i < guess.length(); i++)
        {
            String letter = guess.substring(i, i + 1);

            if (letter.equals(word.substring(i, i + 1)))
            {
                hint += letter;
            }
            else if (word.indexOf(letter) != -1)
            {
                hint += "+";
            }
            else
            {
                hint += "*";
            }
        }

        return hint;
    }
}

Walkthrough Example

HiddenWord puzzle = new HiddenWord("HARPS");
System.out.println(puzzle.getHint("HARMS"));

Hidden word:

HARPS

Guess:

HARMS

Index	Hidden	Guess	Hint
0	H	H	H
1	A	A	A
2	R	R	R
3	P	M	*
4	S	S	S

The result is:

HAR*S

Why This Works

The method checks each guessed letter in the correct order.

If the letter is exactly correct, add the letter.
Otherwise, if the letter exists somewhere in the hidden word, add +.
Otherwise, add *.

Important: The order matters because an exact match should show the actual letter, not a plus sign.

Common Student Mistakes

Mistake 1: Checking indexOf First

Incorrect:

if (word.indexOf(letter) != -1)
{
    hint += "+";
}

This would mark exact matches as +, which is wrong. You must check exact matches first.

Mistake 2: Using == to Compare Strings

Incorrect:

if (letter == word.substring(i, i + 1))

Correct:

if (letter.equals(word.substring(i, i + 1)))

In Java, use .equals() to compare the contents of Strings.

Mistake 3: Forgetting to Return the Hint

The method must return the completed hint.

return hint;

Student-Friendly Summary

The HiddenWord class stores a secret word. The getHint method compares a guess to the secret word one letter at a time.

For each letter:

Situation	Hint Character
Exact match	Show the letter
Wrong spot but in the word	`+`
Not in the word	`*`

The final hint is built one character at a time and returned as a String.