Data Collections · ⁨การเก็บรวบรวมข้อมูล⁩

Learning Objective 4.1.A: Explain the risks to privacy from collecting and storing personal data on computer systems.

• 4.1.A.1 When using a computer, personal privacy is at risk. When developing new programs, programmers should attempt to safeguard the personal privacy of the user.

Learning Objective 4.1.B: Explain the importance of recognizing data quality and potential issues when using a data set.

• 4.1.B.1 Algorithmic bias describes systemic and repeated errors in a program that create unfair outcomes for a specific group of users.
• 4.1.B.2 Programmers should be aware of the data set collection method and the potential for bias when using this method before using the data to extrapolate new information or drawing conclusions.
• 4.1.B.3 Some data sets are incomplete or contain inaccurate data. Using such data in the development or use of a program can cause the program to work incorrectly or inefficiently.

Learning Objective 4.1.C: Identify an appropriate data set to use in order to solve a problem or answer a specific question.

• 4.1.C.1 Contents of a data set might be related to a specific question or topic and might not be appropriate to give correct answers or extrapolate information for a different question or topic.

Learning Objective 4.2.A: Represent patterns and algorithms that involve data sets found in everyday life using written language or diagrams.

• 4.2.A.1 A data set is a collection of specific pieces of information or data.
• 4.2.A.2 Data sets can be manipulated and analyzed to solve a problem or answer a question. When analyzing data sets, values within the set are accessed and utilized one at a time and then processed according to the desired outcome.
• 4.2.A.3 Data can be represented in a diagram by using a chart or table. This visual can be used to plan the algorithm that will be used to manipulate the data.

Learning Objective 4.3.A: Develop code used to represent collections of related data using one-dimensional (1D) array objects.

• 4.3.A.1 An array stores multiple values of the same type. The values can be either primitive values or object references.
• 4.3.A.2 The length of an array is established at the time of creation and cannot be changed. The length of an array can be accessed through the length attribute.
• 4.3.A.3 When an array is created using the keyword new, all of its elements are initialized to the default values for the element data type. The default value for int is 0, for double is 0.0, for boolean is false, and for a reference type is null.
• 4.3.A.4 Initializer lists can be used to create and initialize arrays.
• 4.3.A.5 Square brackets [ ] are used to access and modify an element in a 1D array using an index.
• 4.3.A.6 The valid index values for an array are 0 through one less than the length of the array, inclusive. Using an index value outside of this range will result in an ArrayIndexOutOfBoundsException.

Learning Objective 4.4.A: Develop code used to traverse the elements in a 1D array and determine the result of these traversals.

• 4.4.A.1 Traversing an array is when repetition statements are used to access all or an ordered sequence of elements in an array.
• 4.4.A.2 Traversing an array with an indexed for loop or while loop requires elements to be accessed using their indices.
• 4.4.A.3 An enhanced for loop header includes a variable, referred to as the enhanced for loop variable. For each iteration of the enhanced for loop, the enhanced for loop variable is assigned a copy of an element without using its index.
• 4.4.A.4 Assigning a new value to the enhanced for loop variable does not change the value stored in the array.
• 4.4.A.5 When an array stores object references, the attributes can be modified by calling methods on the enhanced for loop variable. This does not change the object references stored in the array.
• 4.4.A.6 Code written using an enhanced for loop to traverse elements in an array can be rewritten using an indexed for loop or a while loop.

Learning Objective 4.5.A: Develop code for standard and original algorithms for a particular context or specification that involves arrays and determine the result of these algorithms.

• 4.5.A.1 There are standard algorithms that utilize array traversals to:
  • determine a minimum or maximum value
  • compute a sum or average
  • determine if at least one element has a particular property
  • determine if all elements have a particular property
  • determine the number of elements having a particular property
  • access all consecutive pairs of elements
  • determine the presence or absence of duplicate elements
  • shift or rotate elements left or right
  • reverse the order of the elements

Learning Objective 4.6.A: Develop code to read data from a text file.

• 4.6.A.1 A file is storage for data that persists when the program is not running. The data in a file can be retrieved during program execution.
• 4.6.A.2 A file can be connected to the program using the File and Scanner classes.
• 4.6.A.3 A file can be opened by creating a File object, using the name of the file as the argument of the constructor.
  • File(String str) is the File constructor that accepts a String file name to open for reading, where str is the pathname for the file.
• 4.6.A.4 When using the File class, it is required to indicate what to do if the file with the provided name cannot be opened. One way to accomplish this is to add throws IOException to the header of the method that uses the file. If the file name is invalid, the program will terminate.
• 4.6.A.5 The File and IOException classes are part of the java.io package. An import statement must be used to make these classes available for use in the program.
• 4.6.A.6 The following Scanner methods and constructor—including what they do and when they are used—are part of the Java Quick Reference:
  • Scanner(File f) is the Scanner constructor that accepts a File for reading.
  • int nextInt() returns the next int read from the file or input source if available. If the next int does not exist or is out of range, it will result in an InputMismatchException.
  • double nextDouble() returns the next double read from the file or input source. If the next double does not exist, it will result in an InputMismatchException.
  • boolean nextBoolean() returns the next boolean read from the file or input source. If the next boolean does not exist, it will result in an InputMismatchException.
  • String nextLine() returns the next line of text as a String read from the file or input source; can return the empty string if called immediately after another Scanner method that is reading from the file or input source.
  • String next() returns the next String read from the file or input source.
  • boolean hasNext() returns true if there is a next item to read in the file or input source; returns false otherwise.
  • void close() closes this scanner.
  • Exclusion statement: Accepting input from the keyboard is outside the scope of the AP Computer Science A course and exam.
• 4.6.A.7 Using nextLine and the other Scanner methods together on the same input source sometimes requires code to adjust for the methods' different ways of handling whitespace.
  • Exclusion statement: Writing or analyzing code that uses both nextLine and other Scanner methods on the same input source is outside the scope of the AP Computer Science A course and exam.
• 4.6.A.8 The following additional String method—including what it does and when it is used—is part of the Java Quick Reference:
  • String[] split(String del) returns a String array where each element is a substring of this String, which has been split around matches of the given expression del.
  • Exclusion statement: The parameter del uses a format called a regular expression. Writing or analyzing code that uses any of the special properties of regular expressions (e.g., \\*, \\.) is outside the scope of the AP Computer Science A course and exam.
• 4.6.A.9 A while loop can be used to detect if the file still contains elements to read by using the hasNext method as the condition of the loop.
• 4.6.A.10 A file should be closed when the program is finished using it. The close method from Scanner is called to close the file.

Learning Objective 4.7.A: Develop code to use Integer and Double objects from their primitive counterparts and determine the result of using these objects.

• 4.7.A.1 The Integer class and Double class are part of the java.lang package. An Integer object is immutable, meaning once an Integer object is created, its attributes cannot be changed. A Double object is immutable, meaning once a Double object is created, its attributes cannot be changed.
• 4.7.A.2 Autoboxing is the automatic conversion that the Java compiler makes between primitive types and their corresponding object wrapper classes. This includes converting an int to an Integer and a double to a Double. The Java compiler applies autoboxing when a primitive value is:
  • passed as a parameter to a method that expects an object of the corresponding wrapper class
  • assigned to a variable of the corresponding wrapper class
• 4.7.A.3 Unboxing is the automatic conversion that the Java compiler makes from the wrapper class to the primitive type. This includes converting an Integer to an int and a Double to a double. The Java compiler applies unboxing when a wrapper class object is:
  • passed as a parameter to a method that expects a value of the corresponding primitive type
  • assigned to a variable of the corresponding primitive type
• 4.7.A.4 The following class Integer method—including what it does and when it is used—is part of the Java Quick Reference:
  • static int parseInt(String s) returns the String argument as an int.
• 4.7.A.5 The following class Double method—including what it does and when it is used—is part of the Java Quick Reference:
  • static double parseDouble(String s) returns the String argument as a double.

Learning Objective 4.8.A: Develop code for collections of related objects using ArrayList objects and determine the result of calling methods on these objects.

• 4.8.A.1 An ArrayList object is mutable in size and contains object references.
• 4.8.A.2 The ArrayList constructor ArrayList() constructs an empty list.
• 4.8.A.3 Java allows the generic type ArrayList<E>, where the type parameter E specifies the type of the elements. When ArrayList<E> is specified, the types of the reference parameters and return type when using the ArrayList methods are type E. ArrayList<E> is preferred over ArrayList. For example, ArrayList<String> names = new ArrayList<String>(); allows the compiler to find errors that would otherwise be found at run-time.
• 4.8.A.4 The ArrayList class is part of the java.util package. An import statement must be used to make this class available for use in the program.
• 4.8.A.5 The following ArrayList methods—including what they do and when they are used—are part of the Java Quick Reference:
  • int size() returns the number of elements in the list.
  • boolean add(E obj) appends obj to end of list; returns true.
  • void add(int index, E obj) inserts obj at position index (0 <= index <= size), moving elements at position index and higher to the right (adds 1 to their indices) and adds 1 to size.
  • E get(int index) returns the element at position index in the list.
  • E set(int index, E obj) replaces the element at position index with obj; returns the element formerly at position index.
  • E remove(int index) removes element from position index, moving elements at position index + 1 and higher to the left (subtracts 1 from their indices) and subtracts 1 from size; returns the element formerly at position index.
• 4.8.A.6 The indices for an ArrayList start at 0 and end at the number of elements - 1.

Learning Objective 4.9.A: Develop code used to traverse the elements of an ArrayList and determine the results of these traversals.

• 4.9.A.1 Traversing an ArrayList is when iteration or recursive statements are used to access all or an ordered sequence of the elements in an ArrayList.
• 4.9.A.2 Deleting elements during a traversal of an ArrayList requires the use of special techniques to avoid skipping elements.
• 4.9.A.3 Attempting to access an index value outside of its range will result in an IndexOutOfBoundsException.
• 4.9.A.4 Changing the size of an ArrayList while traversing it using an enhanced for loop can result in a ConcurrentModificationException. Therefore, when using an enhanced for loop to traverse an ArrayList, you should not add or remove elements.

Learning Objective 4.10.A: Develop code for standard and original algorithms for a particular context or specification that involve ArrayList objects and determine the result of these algorithms.

• 4.10.A.1 There are standard ArrayList algorithms that utilize traversals to:
  • determine a minimum or maximum value
  • compute a sum or average
  • determine if at least one element has a particular property
  • determine if all elements have a particular property
  • determine the number of elements having a particular property
  • access all consecutive pairs of elements
  • determine the presence or absence of duplicate elements
  • shift or rotate elements left or right
  • reverse the order of the elements
  • insert elements
  • delete elements
• 4.10.A.2 Some algorithms require multiple String, array, or ArrayList objects to be traversed simultaneously.

Learning Objective 4.14.A: Develop code used for linear search algorithms to search for specific information in a collection and determine the results of executing a search.

• 4.14.A.1 Linear search algorithms are standard algorithms that check each element in order until the desired value is found or all elements in the array or ArrayList have been checked. Linear search algorithms can begin the search process from either end of the array or ArrayList.
• 4.14.A.2 When applying linear search algorithms to 2D arrays, each row must be accessed then linear search applied to each row of the 2D array.

Learning Objective 4.15.A: Determine the result of executing each step of sorting algorithms to sort the elements of a collection.

• 4.15.A.1 Selection sort and insertion sort are iterative sorting algorithms that can be used to sort elements in an array or ArrayList.
• 4.15.A.2 Selection sort repeatedly selects the smallest (or largest) element from the unsorted portion of the list and swaps it into its correct (and final) position in the sorted portion of the list.
• 4.15.A.3 Insertion sort inserts an element from the unsorted portion of a list into its correct (but not necessarily final) position in the sorted portion of the list by shifting elements of the sorted portion to make room for the new element.

Learning Objective 4.16.A: Determine the result of calling recursive methods.

• 4.16.A.1 A recursive method is a method that calls itself. Recursive methods contain at least one base case, which halts the recursion, and at least one recursive call. Recursion is another form of repetition.
• 4.16.A.2 Each recursive call has its own set of local variables, including the parameters. Parameter values capture the progress of a recursive process, much like loop control variable values capture the progress of a loop.
• 4.16.A.3 Any recursive solution can be replicated through the use of an iterative approach and vice versa.
  • Exclusion statement: Writing recursive code is outside the scope of the AP Computer Science A course and exam.

Learning Objective 4.17.A: Determine the result of executing recursive algorithms that use strings or collections.

• 4.17.A.1 Recursion can be used to traverse String objects, arrays, and ArrayList objects.

Learning Objective 4.17.B: Determine the result of each iteration of a binary search algorithm used to search for information in a collection.

• 4.17.B.1 Data must be in sorted order to use the binary search algorithm. Binary search starts at the middle of a sorted array or ArrayList and eliminates half of the array or ArrayList in each recursive call until the desired value is found or all elements have been eliminated.
• 4.17.B.2 Binary search is typically more efficient than linear search.
  • Exclusion statement: Search algorithms other than linear and binary search are outside the scope of the AP Computer Science A course and exam.
• 4.17.B.3 The binary search algorithm can be written either iteratively or recursively.

Learning Objective 4.17.C: Determine the result of each iteration of the merge sort algorithm when used to sort a collection.

• 4.17.C.1 Merge sort is a recursive sorting algorithm that can be used to sort elements in an array or ArrayList.
  • Exclusion statement: Sorting algorithms other than selection, insertion, and merge sort are outside the scope of the AP Computer Science A course and exam.
• 4.17.C.2 Merge sort repeatedly divides an array into smaller subarrays until each subarray is one element and then recursively merges the sorted subarrays back together in sorted order to form the final sorted array.