AP Computer Science A Review

AP Exam Topic List

This is essentially a full, unit-by-unit guide of all the topics covered on the AP Exam. More detailed explanations of each topic are offered in the unit pages (see table of contents).

Unit 1: Primitive Types

Printing and literals

• Printing with System.out.print and System.out.println

  • The difference between these two methods

• Literals, including string literals

Variables and data types

• Concept of a type

• Primitive vs. reference types

• Primitive types for AP CSA: int, double, boolean

  • When each is appropriate

  char is not assessed on the AP Exam

• Limitations on int

  • 4 byte size
  • Valid range of integers (using the static constants of Integer, not the literal values)
  • Integer overflow concept

• Concept of a variable

• Declaring variables

• The final keyword

Expressions

• Arithmetic operations on int and double values

  • Arithmetic operators: +, -, *, /, %
  • Compound expressions using these operators

• Operator precedence (i.e. order of operations)

• ArithmeticException upon dividing by zero

• Integer math vs. double math and when each is used

Using variables and data types

• Assignment operator: =

  • Evaluation of any expressions on the right, then assignment to the variable

• Compound assignment operators: +=, -=, *=, /=, %=

• Increment and decrement operators: ++, --

• Casting with int and double

  • Widening vs. narrowing casting
  • Truncation

• Rounding with the casting operators

Unit 2: Using Objects

• Object vs. class distinction

Class constructors

• Purpose of the constructor: to set the initial state of an object

• Constructor signatures: name and parameter list

  • Parameters have a name and type

• Constructors have the same name as the class

• Formal vs. actual parameters

• "Call by value" as it applies to constructors

• Overloaded constructors

• new keyword and calling a constructor

  • Also applies to classes written by other programmers
  • Proper parameter(s) (or none, if there is a no-argument constructor) must be passed in

Methods of an object

• Concept of an object's methods (collectively, its behavior)

• Method signatures: method name, parameter list, and return type

• void return type

• Overloaded methods

• Call methods with the dot operator (.) and parameter(s), if applicable

  • Proper parameter(s), or none (if applicable), must be passed in

• Flow of control when calling a method

  • A method call interrupts the execution of the caller to execute the method
  • Once the method is done executing, the execution of the caller resumes

• Use return values of methods

String, Integer, Double, Math

• Grouping of classes into packages

  • The above classes (in the heading of this section) are all members of the java.lang package
  • java.lang does not need to be imported

• Basic concept of APIs and libraries: to simplify complex tasks

String

• Create String objects; two methods:

  • String literals
  • String constructor

• Immutability of String objects

• Concatenation of String objects

  • A new String is created because Strings are immutable
  • Concatenating a primitive to a String implicitly converts the primitive to a String
  • Concatenating an object to a String implicitly calls the object's toString method to convert it to a String

• Escape sequences: \". \\, \n

• Valid String indices

  • StringIndexOutOfBoundsException

• String methods on the Java Quick Reference

  • Use of substring method of a String to retrieve the element at index i, i.e. single element substring

Integer and Double wrapper classes

• Distinction between the wrapper classes and the associated primitives

• Integer and Double methods on the Java Quick Reference

• Autoboxing and unboxing

  • Occurs as needed when passing values to a method or when assigning values to variables

Math class

• Call static methods with the class name

• Math static methods on the Java Quick Reference

  • Generate random values inside a specified range with Math.random

Miscellaneous

• Abstraction with methods

• null keyword

  • Variables of a reference type can hold either null or a reference to an object

    Dog one = null;         // null value
    Dog two = new Dog();    // reference to an object
    

  • In the case of the latter, the reference is a pointer to the memory location of the actual object
  • NullPointerException when trying to perform certain operations with a null reference

Unit 3: Boolean Expressions and if Statements

Boolean expressions

• Relational equality operators: ==, !=

• Relational comparison operators: <, <=, >, >=

• Write/evaluate Boolean expressions with these relational operators

Conditional statements

• Purpose behind conditional statements

• Write/use if statements (also known as a one-way selection)

• Write/use if-else statements (also known as a two-way selection)

• Incorporate else if statements into if and if-else statements (multi-way selection)

• Difference between and when to use if vs. if-else statements, as well as when to incorporate else if statements

• Nested if statements

Compound Boolean expressions

• Logical operators: !, &&, ||

  • Operator precedence for logical operators (which is the same as the order in which they are listed above)

• Write/evaluate compound Boolean expressions with these logical operators

• Short-circuited evaluation

• De Morgan's logic laws

• Truth tables

• Understand the concept of equivalent Boolean expressions

Object comparison

• Aliases (in the context of object references)

  • Use of the relational equality operators to determine if two object references are aliases

• Use of the relational equality operators and null to determine if a variable of a reference type points to an actual object

• .equals methods to check for equivalency

• Equivalency vs. equality for objects

Unit 4: Iteration

Iteration statements

• Understand the purpose behind iteration

• Write/use while loops

  • Boolean expression inside the loop header

• Write/use for loops

  • Three parts of the loop header

• Flow of control for these loops

  • while loop: Repetition until the Boolean expression evaluates to false
  • for loop: Initialization statement, then repetition until the Boolean expression evaluates to false, with the increment statement after each iteration

• Rewrite for loops as while loops and vice versa

• Infinite loops

• Loops that never execute

• Return statements inside loops

• Off by one errors

Iterative algorithms

• Identify, modify, and develop the following algorithms:
  • Check for divisibility
  • List the digits of an integer
  • Determine how often a specific criterion is met
  • Determine a minimum or maximum value
  • Determine a sum
  • Determine an average
  • Determine a mode
  • Determine if and how many substrings meet a certain criterion
  • Reverse a string

Nested iteration

• Write/use nested loops

• Flow of control for these loops

  • Inner loop must finish executing before outer loop continues

Miscellaneous

• Determine how many times a specific statement executes

• Compare two loops

Unit 5: Writing Classes

About classes and objects

• Access modifiers (public and private only)

  • Classes: public
  • Instance variables: private
  • Constructors: public
  • Methods: public or private

• Data encapsulation

  • private access modifier and accessor/mutator methods to achieve this

• Object state and the "has-a" relationship

Constructors

• Write constructors to establish initial object state

• Purpose and use of constructor parameters to set state

• Not destroying/modifying objects provided as parameters to the constructor – store a copy of the object in an instance variable instead

  Destroying persistent data on the AP Exam FRQs will result in a score penalty.

• Default no-argument constructor

Comments, documentation, and pre/postconditions

• Describe code with comments and understand their purpose

• The three types of Java comments (single-line, block, Javadoc)

• Preconditions

  There is no expectation that you check input against the preconditions when writing FRQs, and it will result in a score penalty if you write an incorrect check.

• Postconditions

Writing methods

• The concept of methods – input is usually passed in, something is done, and sometimes a value is returned

• Write methods to perform tasks with input/return values

• Void vs. non-void methods

• Declaring return types

• "Return by value"

  • With object references as return values, the reference is copied, not the object

• private access modifier rules apply to parameters

• Not destroying/modifying objects provided as parameters to methods unless required

  Destroying persistent data on the AP Exam FRQs will result in a score penalty.

• Formal parameter initialization

  • Primitive actual parameters are copied
  • Reference actual parameters are copied – the reference, not the object
    • Formal and actual parameter become aliases

Static members

• The concept that static members are associated with a class, not an object

  • Static methods cannot change instance data or use non-static methods – only static variables and methods

• Write static methods and declare static variables

• Call static methods and use static variables

  • Class name and dot operator

• static keyword

• No this reference

Accessor and mutator methods

• Write/understand the purpose of accessor (getter) methods

• Write/understand the purpose of mutator (setter) methods

Scope, access, and this

• Local scope

  • Cannot be declared with access modifiers
  • Can only be accessed within the defining method (or constructor)

• Local variables have precedence over instance variables when they have the same name

• this keyword

  • Use as a method parameter

Miscellaneous

• The toString method, its purpose, and how to override it

• Understand that the toString method is implicitly called when an object is passed to one of the print methods

• Method decomposition

The ethical and social implications of computing are not assessed on the AP Exam.

Unit 6: Array

Creating and accessing arrays

• Concept and purpose of an array

  • Can store primitive or reference data

• Array creation syntax with new

• Array access syntax with square brackets

• Create and modify arrays

• Array size is fixed

• Default values for array elements

  • For arrays of int, double, boolean, and reference types

• Initializer lists

• Valid array indices

  • Arrays are zero-indexed
  • ArrayIndexOutOfBoundsException

Traversing arrays

• Meaning of "traversing an array"

• Use for or while loops to traverse arrays with indices

• Use enhanced for loops to traverse arrays with the enhanced for loop variable

  • Values stored in the enhanced for loop variable are copies of the array elements
  • Enhanced for loop cannot be used to edit the array values

• Awareness of and avoidance of off by one errors

Array algorithms

• Identify, modify, and develop the following algorithms:
  • Determine a minimum or maximum value
  • Determine a sum
  • Determine an average
  • Determine a mode
  • Determine if and how many elements meet a certain criterion
  • Determine the consecutive pairs of elements that exist within the array
  • Determine if duplicate elements exist in the array
  • Shift elements in one direction
  • Reverse the array elements

Unit 7: ArrayList

Understanding and creating ArrayLists

• Differences between arrays and ArrayList

• Properties of an ArrayList

  • Stores reference types only
  • Mutable data of a dynamic size

• ArrayList creation syntax with constructor

• Generic typing vs. non-generic typing

  • Advantages of using generic typing

• Importing ArrayList from the java.util package

Manipulating and traversing ArrayLists

• ArrayList methods in the Java Quick Reference

• Utilize the ArrayList methods to modify ArrayLists

• Traverse an ArrayList with for, while, and enhanced for loops

  • Properly handle indices that change when an element is removed

• Valid indices for ArrayLists

  • ArrayLists are zero-indexed
  • IndexOutOfBoundsException

• ConcurrentModificationException when modifying an ArrayList while traversing it with an enhanced for loop

ArrayList algorithms

• Identify, modify, and develop the following algorithms:

  • Insert elements while traversing the ArrayList
  • Remove elements while traversing the ArrayList
  • + all algorithms for arrays

• Be able to traverse multiple objects simultaneously to execute these algorithms

Searching and sorting

These topics are applicable to both arrays and ArrayLists.

• Understand and apply the following algorithms:

  • Sequential search (also called linear search)
  • Selection sort
  • Insertion sort

• Compare these algorithms based on the number of times specified statements execute

The ethical issues regarding data collection are not assessed on the AP Exam.

Unit 8: 2D Array

Creating and accessing 2D arrays

• "Array of arrays" concept

• 2D array creation syntax with new

• 2D array access syntax with sets of square brackets

• Create and modify 2D arrays

• Initializer lists for 2D arrays

• Row-major vs. column-major order

  The AP Exam uses row-major order.

Traversing 2D arrays

• Nested loops

• Use nested for and nested enhanced for loops to traverse 2D arrays

• Traversing the 2D array in row-major vs. column-major order

2D array algorithms

• Identify, modify, and develop all array algorithms with 2D arrays

• Sequential/linear search

Unit 9: Inheritance

Superclass-subclass relationship

• Concept of a superclass and subclass

  • Extension of superclass data and functionality with subclass

• Concept of class hierarchy

• "is-a" relationship between subclass and superclass

• extends keyword to define a subclass

• Subclasses may only have one superclass

Applying inheritance

• Call superclass constructors and methods with super and parameters, if applicable

• Implicit call to no-argument superclass constructor when there is no explicit call

• Execution order of constructors in the class hierarchy

  • Constructor calls from bottom (subclass) to top (Object), then constructor execution from top (Object) to bottom (subclass)

• Method overriding in subclasses

• Additional methods and instance variables in subclasses

• The subclass inherits public methods but not constructors

• Understand and apply polymorphism

  • Reference of a superclass may refer to an object of the superclass or subclass(es)
  • Reference of a superclass cannot call any subclass methods unless they are also defined in the superclass
  • If a method is declared in a superclass and subclass, a method call on an object of the subclass stored in a variable declared with the superclass type executes the method in the subclass, not the superclass

• Object class (java.lang package) as a superclass of all classes

  • Object methods in the Java Quick Reference

Unit 10: Recursion

Recursion as a concept

• Concept of recursion and its applications

• Components of a recursive method, i.e. base case and recursive method call

• Unique local variables for each recursive method call, including parameters, which indicate the progress of the recursion

• Recursion vs. iteration

• Understand traversal of various objects and data structures with recursion

• Determine the result of a recursive method

Writing recursive code is not assessed on the AP Exam.

Searching and sorting with recursion

• Binary search

• Merge sort