Provided Code

public class Phrase
{
    private String currentPhrase;

        public Phrase(String p) {
        currentPhrase = p;
    }

    public int findNthOccurrence(String str, int n)
    { /* to be implemented in part (a) */ }

    public void replaceNthOccurrence(String str, int n, String repl)
    { /* to be implemented in part (b) */ }

    public int findLastOccurrence(String str)
    { /* to be implemented in part (c) */ }

        public String toString() {
        return currentPhrase;
    }
}

Part A — findNthOccurrence (5 Points)

Write findNthOccurrence(). Return the index of the nth occurrence of str in currentPhrase, or -1 if fewer than n occurrences exist.

Check Answer Clear

public int findNthOccurrence(String str, int n)
{
    int index = currentPhrase.indexOf(str);
    int count = 1;

    while (index != -1 && count < n)
    {
        index = currentPhrase.indexOf(str, index + 1);
        count++;
    }

    if (count == n)
        return index;
    return -1;
}

Part B — replaceNthOccurrence (2 Points)

Write replaceNthOccurrence(). Replace the nth occurrence of str with repl in currentPhrase. If fewer than n occurrences exist, currentPhrase is unchanged.

Check Answer Clear

public void replaceNthOccurrence(String str, int n, String repl)
{
    int index = findNthOccurrence(str, n);

    if (index != -1)
    {
        currentPhrase = currentPhrase.substring(0, index)
                      + repl
                      + currentPhrase.substring(index + str.length());
    }
}

Part C — findLastOccurrence (2 Points)

Write findLastOccurrence(). Return the index of the last occurrence of str in currentPhrase, or -1 if it does not appear.

Check Answer Clear

public int findLastOccurrence(String str)
{
    int index = -1;
    int next = findNthOccurrence(str, 1);
    int n = 1;

    while (next != -1)
    {
        index = next;
        n++;
        next = findNthOccurrence(str, n);
    }

    return index;
}

Frequently Asked Questions