Documentation with Comments
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AP Computer Science A › Documentation with Comments
The implementation of the addMoney method is incorrect because it does not meet its postcondition. Why?
The method should be named setMoney instead of addMoney.
The balance variable should be a public instance variable.
The method assigns amount to balance instead of adding to it.
The precondition amount > 0 is not checked inside the method.
Explanation
The postcondition states that the balance is increased by amount. The code balance = amount; sets the balance equal to the amount, overwriting the previous value. The correct implementation would be balance += amount; or balance = balance + amount;. Therefore, the implementation fails to meet the specified postcondition.
The setScore method is intended to update an instance variable named score. Why does this implementation fail to meet its documented postcondition?
The method should return the new score to confirm it has been set.
The method declares a new local variable score instead of assigning to the instance variable.
The parameter newScore shadows the instance variable score.
A precondition is missing to check if newScore is positive.
Explanation
The line int score = newScore; declares a new local variable named score that exists only within the method. It does not affect the instance variable of the same name. To meet the postcondition, the line should be this.score = newScore; or simply score = newScore; (without the type declaration int).
The precondition 'The player's current position is valid' is documented for the movePlayer method. Why is this statement considered a precondition?
It describes the purpose of the numSpaces parameter.
It describes a condition related to the object's state that must be true before the method is called.
It describes the value that will be returned by the method.
It describes the state of the player object after the method has finished executing.
Explanation
A precondition is a requirement on the state of the program or the method's inputs that must be met before the method is invoked. This statement concerns the player's position prior to the move, making it a classic example of a precondition.
The documentation for getFirstChar states that word should be a non-empty string. Which of the following is an additional, unstated precondition required to prevent a run-time error?
The word parameter must not contain any spaces.
The method must return a lowercase character.
The word parameter must have a length greater than 1.
The word parameter must not be null.
Explanation
If the word parameter is null, the call word.charAt(0) will result in a NullPointerException. The documented precondition 'non-empty' ensures the length is greater than 0, but it does not prevent a null value from being passed. Therefore, word not being null is a necessary, unstated precondition.
Consider the provided calculateArea method. Which of the following statements best describes a precondition for this method?
The area is determined by multiplying the width and height parameters.
The width and height parameters must represent positive values.
The width and height parameters must be of type int.
The method must return a positive value representing the area.
Explanation
A precondition is a condition that must be true before a method is called for it to work as intended. The comment explicitly states 'Precondition: width > 0 and height > 0', which means the parameters must be positive values. Choice B describes a postcondition (what is true after the method runs). Choice C contradicts the method signature, which specifies double parameters. Choice D describes the implementation details, not a condition for the method's use.
Based on the postcondition provided in the documentation, what is guaranteed to be true after a call to replaceAll?
The words list will no longer contain any instances of the target string.
The words list will be sorted alphabetically.
The words list will contain at least one instance of the replacement string.
The size of the words list will remain unchanged.
Explanation
The postcondition states that every element that was equal to target is now equal to replacement. This implies that after the method executes, no elements equal to target will remain. Choice A is not guaranteed; if target was not in the list originally, replacement will not be added. Choice C is an implicit postcondition but not the one explicitly described. Choice D is incorrect; the method only replaces elements and does not sort them.
Which of the following would be an appropriate postcondition to include in the documentation for the sortStrings method?
The elements of list are arranged in non-decreasing alphabetical order.
The list parameter is not null.
The list parameter contains at least one String object.
The method uses an efficient sorting algorithm to reorder the list.
Explanation
A postcondition describes the state after the method completes. Since the method's purpose is to sort the list, the statement that the list's elements are in sorted order is a direct and essential postcondition. Choices A and D describe preconditions that should be true before the method is called. Choice C describes an implementation detail, which is not part of the contract defined by postconditions.
What is the purpose of the comments in the provided StudentRecord code snippet?
They act as executable code that calculates GPA automatically.
They primarily conceal grades to ensure privacy and security.
They indicate syntax errors the compiler will repair later.
They document data handling and formulas to support maintenance.
Explanation
This question tests AP Computer Science A documentation with comments, specifically their role in documenting data structures and calculations. Comments in classes that manage data help explain how information is stored, processed, and calculated, which is crucial for maintaining academic or business logic. In the StudentRecord code, comments document how grades are stored, how GPA calculations work, and any assumptions about the data format. Choice B is correct because comments document data handling procedures and calculation formulas, supporting future maintenance and modifications. Choice A is incorrect because it fundamentally misunderstands comments - they are not executable code and cannot perform any calculations or data processing. Students should learn to document complex calculations and data transformations thoroughly. Encourage commenting mathematical formulas and business rules to preserve institutional knowledge.
In the StudentRecord code below, what information do the inline comments provide in this program?
import java.util.ArrayList;
import java.util.List;
/**
* Maintains quiz scores and computes an average.
* Demonstrates how inline comments can justify small design choices.
*/
public class StudentRecord {
private final List<Integer> quizScores = new ArrayList<>();
/**
* Adds a quiz score from 0 to 10.
*
* @param score the quiz score
* @return true if the score is stored
*/
public boolean addQuizScore(int score) {
if (score < 0 || score > 10) {
// Enforce the stated scale so the average remains interpretable.
return false;
}
quizScores.add(score);
return true;
}
/**
* Computes the arithmetic mean of stored quiz scores.
*
* @return the average, or 0.0 if no scores exist
*/
public double averageScore() {
if (quizScores.isEmpty()) {
// Avoid dividing by zero when no scores have been added.
return 0.0;
}
int sum = 0;
for (int score : quizScores) {
// Accumulate the total to compute the mean in one pass.
sum += score;
}
return (double) sum / quizScores.size();
}
}
They are decorative and cannot help a future programmer understand the method’s behavior.
They increase numerical precision by forcing integer sums to be stored as doubles.
They are executable commands that prevent the loop from running when scores are low.
They justify validation and explain why special cases, like empty lists, need safeguards.
Explanation
This question tests AP Computer Science A documentation with comments, specifically understanding how inline comments provide implementation details and justify design choices. Inline comments within methods explain specific logic decisions and help prevent common programming errors. In this StudentRecord code, the inline comments justify the 0-10 score validation, explain why empty list checking prevents division by zero, and clarify the accumulation logic in the averaging calculation. Choice A is correct because the comments justify validation logic and explain why special cases like empty lists need safeguards to prevent runtime errors. Choice B is incorrect because comments are not executable commands - they cannot control program flow or prevent loops from running. When teaching inline comments, encourage students to document edge cases and explain any non-obvious logic. Show how comments can serve as reminders about why certain checks are necessary, preventing future maintainers from accidentally removing important safeguards.
In the LibraryManager code below, what is the purpose of the comments in the provided code snippet?
import java.util.HashSet;
import java.util.Set;
/**
* Tracks a set of unique book titles for a small library catalog.
* Comments illustrate why specific validations are performed.
*/
public class LibraryManager {
private final Set<String> titles = new HashSet<>();
/**
* Adds a title to the catalog.
*
* @param title the title to add
* @return true if the catalog changed
*/
public boolean addBook(String title) {
if (title == null) {
// Null titles provide no searchable value.
return false;
}
String normalized = title.trim();
if (normalized.isEmpty()) {
// Blank strings are rejected to avoid cluttering the catalog.
return false;
}
return titles.add(normalized);
}
/**
* Determines whether a title exists in the catalog.
*
* @param title the title to check
* @return true if present; false otherwise
*/
public boolean contains(String title) {
if (title == null) {
return false;
}
// Trim to treat leading/trailing spaces as insignificant.
return titles.contains(title.trim());
}
}
They encrypt the stored titles so only authorized users can read the catalog.
They explain validation and normalization decisions, making future changes safer and clearer.
They function as executable checks that the Set uses to reject duplicates automatically.
They improve performance by allowing the compiler to skip trimming operations at runtime.
Explanation
This question tests AP Computer Science A documentation with comments, specifically understanding how comments explain validation logic and design decisions. Comments provide crucial context for understanding why certain checks and normalizations are performed in code. In this LibraryManager code, comments explain why null titles are rejected, why blank strings are filtered out, and why trimming is used for normalization - all decisions that make the catalog more robust and consistent. Choice A is correct because the comments explain validation and normalization decisions, making future changes safer by documenting the reasoning behind each check. Choice C is incorrect because comments are not executable - the Set's duplicate rejection is a feature of the HashSet data structure, not the comments. When teaching comment writing, have students explain their validation logic in comments, focusing on the business reasons behind technical decisions. This practice helps maintain code quality when requirements change.