AP CSA free response question types study guide

Define a method to calculate the factorial.

public int factorial(int n) { return (n <= 1) ? 1 : n * factorial(n - 1); }

True or False: Methods can return multiple values.

False - A method can only return one value. Use arrays or objects for multiple values.

Fill in the blank: A ____ is a block of code that performs a specific task.

method

Write a method to check if a string is a palindrome.

public boolean isPalindrome(String str) { String rev = new StringBuilder(str).reverse().toString(); return str.equals(rev); }

What is the purpose of the 'this' keyword?

'this' refers to the current object instance, allowing access to its attributes and methods.

Create a method to find the maximum in an array.

public int findMax(int[] arr) { int max = arr[0]; for (int num : arr) { if (num > max) { max = num; } } return max; }

True or False: A constructor can have a return type.

False - Constructors do not have a return type, not even void.

What do the 'static' and 'instance' methods represent?

Static methods belong to the class; instance methods belong to an object. Static can be called without an instance.

Write a method to count vowels in a string.

public int countVowels(String str) { int count = 0; for (char c : str.toCharArray()) { if ('aeiouAEIOU'.indexOf(c) != -1) { count++; } } return count; }

Compare method overloading and overriding.

Overloading: Same method name, different parameters. Overriding: Same method name and parameters in a subclass.

Show an example of a simple class with a method.

class Dog { String name; Dog(String name) { this.name = name; } void bark() { System.out.println("Woof!"); } }

What does the keyword 'void' signify in a method?

Void signifies that the method does not return a value.

Write a method that reverses an array.

public void reverseArray(int[] arr) { int left = 0, right = arr.length - 1; while (left < right) { int temp = arr[left]; arr[left++] = arr[right]; arr[right--] = temp; } }

True or False: A method can be called before it is defined.

True - If the method is defined within the same class or is a static method.

Create a method to calculate the sum of two integers.

public int sum(int a, int b) { return a + b; }

What is the significance of method parameters?

Parameters allow methods to accept inputs, which can be used within the method to perform operations.

What is encapsulation?

Encapsulation is the bundling of data and methods that operate on that data within a single unit, typically a class. It restricts direct access to some components.

True or False: Inheritance promotes code duplication.

False. Inheritance allows a new class to inherit methods and properties from an existing class, promoting code reuse.

Define polymorphism.

Polymorphism allows methods to do different things based on the object that it is acting upon. This can be achieved through method overriding or interfaces.

Fill in the blank: A ____ is a blueprint for creating objects.

class

Compare interfaces and abstract classes.

Interfaces: only method signatures, no implementation. Abstract classes: can have implemented methods and can hold state.

What is a constructor?

A constructor is a special method called when an object is instantiated. It initializes the object's properties.

Cause → Effect: Why use an interface?

To define a contract that implementing classes must follow, ensuring they provide specific methods.

What is method overriding?

Method overriding allows a subclass to provide a specific implementation of a method that is already defined in its superclass.

True or False: A class can implement multiple interfaces.

True. A class in Java can implement multiple interfaces, allowing for more flexible design.

What is the purpose of access modifiers?

Access modifiers (public, private, protected) control the visibility of classes, methods, and variables, protecting data integrity.

Give an example of composition.

A Car class that contains an Engine class as a member. The Car 'has-a' Engine.

Define aggregation.

Aggregation is a 'has-a' relationship where the contained objects can exist independently of the containing object.

What is algorithm efficiency?

Algorithm efficiency refers to the amount of computational resources (time and space) required by an algorithm to complete its task.

True or False: More loops always mean slower performance.

False. The performance depends on loop complexity and other factors, not just the number of loops.

O(n) vs O(n^2): Which is faster?

O(n) is generally faster than O(n^2) for larger input sizes because it scales linearly compared to quadratic growth.

Fill in the blank: The time complexity of a binary search is ______.

O(log n) - it divides the search interval in half each time.

Cause → Effect: Increasing recursion depth leads to what?

Increased memory usage - each recursive call adds to the call stack.

What are common methods for analyzing algorithms?

- Big O notation - Best, average, worst-case analysis - Space complexity

What does 'base case' mean in recursion?

The base case is a condition that stops the recursive calls, preventing infinite recursion.

Compare iterative and recursive approaches.

Iterative: uses loops, generally more memory efficient. Recursive: uses function calls, more intuitive for problems like tree traversals.

True or False: Every recursive algorithm can be rewritten as an iterative algorithm.

True. Any recursive algorithm can be converted to iterative form, often using a stack.

Example of algorithm efficiency: Sorting.

Consider Bubble Sort: O(n^2) vs Quick Sort: O(n log n). Quick Sort is more efficient.

What is the purpose of loop invariants?

Loop invariants help prove the correctness of loops by establishing a condition that holds before and after each iteration.

Define the term 'tail recursion'.

Tail recursion occurs when the recursive call is the last operation in the function, allowing for optimizations.

Array vs. ArrayList: Key difference?

Arrays have a fixed size, while ArrayLists can dynamically resize as elements are added or removed.

True or False: Maps store data in key-value pairs.

True - Maps use unique keys to associate with specific values, allowing for efficient data retrieval.

Fill in the blank: A list that allows duplicates is called a __________.

ArrayList - Unlike sets, ArrayLists can contain multiple occurrences of the same element.

Give an example of when to use a Map.

Use a Map when you need to associate student IDs with student names for quick lookups.

What is the time complexity of accessing an array element?

O(1) - Accessing an element by index in an array is constant time.

Linked List vs. Array: When is a linked list better?

Linked lists are better for frequent insertions/deletions as they don't require shifting elements.

Cause → Effect: Using a HashMap for lookups.

Cause: Using a HashMap for lookups. Effect: Achieves average O(1) time complexity for retrieval.

What is the primary use of a Stack?

Stacks are used for managing function calls, reversing data, and implementing backtracking algorithms.