AP Computer Science a Flashcards: 2d Array Creation And Access

What this deck covers

This deck focuses on 2d Array Creation And Access, giving you a quick way to review the definitions, rules, and examples that matter most for AP Computer Science a.

How to use these flashcards

Work through these flashcards in short sessions. Try to answer each prompt before flipping the card, then revisit any cards you miss until the explanation feels automatic.

Flashcard 1: Which method accesses the element at row 2, column 1?

Answer: array[2][1];. First index specifies row, second index specifies column.

Flashcard 2: What is the index of the first row and first column in a 2D array?

Answer: [0][0]. Arrays use zero-based indexing for both dimensions.

Flashcard 3: How many elements are in a 2D array of size 4x5?

Answer: 20 elements. Total elements equals rows multiplied by columns: $4 \times 5 = 20$.

Flashcard 4: What is an example of a rectangular 2D array?

Answer: int[][] array = new int[3][3];. All rows have same length, forming regular matrix shape.

Flashcard 5: How do you access the second column of the first row in a 2D array?

Answer: array[0][1]. Second index (1) selects the second column position.

Flashcard 6: Identify the method to get the number of rows in a 2D array.

Answer: array.length. Length property returns the number of rows in the array.

Flashcard 7: How do you declare a 2D array in Java?

Answer: int[][] arrayName;. Declaration syntax uses double brackets for 2D array type.

Flashcard 8: How do you define a 2D array with specific values?

Answer: int[][] array = {{1, 2}, {3, 4}};. Initializer list syntax creates array with literal values.

Flashcard 9: What is the purpose of nested loops in 2D arrays?

Answer: To iterate through rows and columns. Outer loop handles rows, inner loop handles columns.

Flashcard 10: How do you declare a 2D array to store Strings?

Answer: String[][] array;. Declaration syntax for String object references in 2D array.

Flashcard 11: How do you access the last element of the last row in a 2D array?

Answer: array[array.length - 1][array[array.length - 1].length - 1]. Uses length properties to calculate final position indices.

Flashcard 12: What is the index of the first row and first column in a 2D array?

Answer: [0][0]. Arrays use zero-based indexing for both dimensions.

Flashcard 13: What is a 2D array?

Answer: A data structure storing elements in a grid with rows and columns. Elements arranged in matrix format with row and column indices.

Flashcard 14: How do you initialize a 3x3 int 2D array in Java?

Answer: int[][] array = new int[3][3];. Creates a 3x3 matrix with new keyword and size specification.

Flashcard 15: How do you create a 2D array with 5 rows and variable columns?

Answer: int[][] array = new int[5][];. Creates row structure without specifying column dimensions.

Flashcard 16: What is the syntax to iterate over all elements in a 2D array?

Answer: for (int i = 0; i < array.length; i++) for (int j = 0; j < array[i].length; j++). Nested loops traverse rows first, then columns within each row.

Flashcard 17: How do you access the second column of the first row in a 2D array?

Answer: array[0][1]. Second index (1) selects the second column position.

Flashcard 18: What is the syntax to iterate over all elements in a 2D array?

Answer: for (int i = 0; i < array.length; i++) for (int j = 0; j < array[i].length; j++). Nested loops traverse rows first, then columns within each row.

Flashcard 19: What is an example of initializing a jagged 2D array?

Answer: int[][] array = { {1, 2}, {3, 4, 5} };. Different row lengths create irregular array structure.

Flashcard 20: What is the time complexity for accessing an element in a 2D array?

Answer: O(1). Direct indexing provides constant time element access.

Flashcard 21: How do you create a 2D array with 5 rows and variable columns?

Answer: int[][] array = new int[5][];. Creates row structure without specifying column dimensions.

Flashcard 22: What is the default value of elements in a new int 2D array?

Answer:

1. Java initializes numeric array elements to zero by default.

Flashcard 23: What is the length of a 2D array row array[0]?

Answer: array[0].length. Returns number of columns in the specified row.

Flashcard 24: What is an example of a rectangular 2D array?

Answer: int[][] array = new int[3][3];. All rows have same length, forming regular matrix shape.

Flashcard 25: Identify the method to get the number of rows in a 2D array.

Answer: array.length. Length property returns the number of rows in the array.

Flashcard 26: What is the result of accessing out-of-bounds index in a 2D array?

Answer: ArrayIndexOutOfBoundsException. Runtime exception thrown when index exceeds array bounds.

Flashcard 27: What will array.length return for a 4x6 2D array?

Answer:

1. Length property returns number of rows in the array.

Flashcard 28: How do you declare a char 2D array?

Answer: char[][] array;. Declaration syntax for character data type in 2D format.

Flashcard 29: What is the purpose of nested loops in 2D arrays?

Answer: To iterate through rows and columns. Outer loop handles rows, inner loop handles columns.

Flashcard 30: What is a jagged array?

Answer: A 2D array where rows have different lengths. Each row can have different number of columns.

Flashcard 31: How do you initialize a 2D array with 2 rows and 3 columns?

Answer: int[][] array = new int[2][3];. Specifies exact dimensions during array creation.

Flashcard 32: What is the default value of elements in a new int 2D array?

Answer:

1. Java initializes numeric array elements to zero by default.

Flashcard 33: How many elements are in a 2D array of size 4x5?

Answer: 20 elements. Total elements equals rows multiplied by columns: $4 \times 5 = 20$.

Flashcard 34: How do you define a 2D array with specific values?

Answer: int[][] array = {{1, 2}, {3, 4}};. Initializer list syntax creates array with literal values.

Flashcard 35: What is the default value of a boolean 2D array?

Answer: false. Java initializes boolean array elements to false by default.

Flashcard 36: How do you check if a 2D array element is zero?

Answer: if (array[i][j] == 0). Conditional statement compares element value to zero.

Flashcard 37: How do you declare a 2D array reference of any type?

Answer: Type[][] array;. Generic declaration syntax for any reference type.

Flashcard 38: How do you declare a 2D array reference of any type?

Answer: Type[][] array;. Generic declaration syntax for any reference type.

Flashcard 39: How do you check if a 2D array is empty?

Answer: Check if array.length == 0 or array[0].length == 0. Check both row count and first row column count.

Flashcard 40: What is an example of initializing a jagged 2D array?

Answer: int[][] array = { {1, 2}, {3, 4, 5} };. Different row lengths create irregular array structure.

Flashcard 41: How do you check if a 2D array element is zero?

Answer: if (array[i][j] == 0). Conditional statement compares element value to zero.

Flashcard 42: How do you initialize a 3x3 int 2D array in Java?

Answer: int[][] array = new int[3][3];. Creates a 3x3 matrix with new keyword and size specification.

Flashcard 43: What is the time complexity for accessing an element in a 2D array?

Answer: O(1). Direct indexing provides constant time element access.

Flashcard 44: How do you update the element at row 1, column 2 to 10?

Answer: array[1][2] = 10;. Assignment syntax uses array notation with row and column indices.

Flashcard 45: How do you access the last element of the last row in a 2D array?

Answer: array[array.length - 1][array[array.length - 1].length - 1]. Uses length properties to calculate final position indices.

Flashcard 46: Identify the method to get the number of columns in the first row.

Answer: array[0].length. Accesses the length property of the first row array.

Flashcard 47: How do you initialize a 2D array with specific String values?

Answer: String[][] array = {{"a", "b"}, {"c", "d"}};. Initializer syntax with String literals in nested structure.

Flashcard 48: What is a 2D array?

Answer: A data structure storing elements in a grid with rows and columns. Elements arranged in matrix format with row and column indices.

Flashcard 49: What is the default value of a boolean 2D array?

Answer: false. Java initializes boolean array elements to false by default.

Flashcard 50: What is the result of accessing out-of-bounds index in a 2D array?

Answer: ArrayIndexOutOfBoundsException. Runtime exception thrown when index exceeds array bounds.

Flashcard 51: Which keyword is used to create a new 2D array in Java?

Answer: new. Required keyword for dynamic memory allocation in Java.

Flashcard 52: What is the syntax to assign 'A' to the first element of a 2D char array?

Answer: array[0][0] = 'A';. Assignment uses array indexing with character literal value.

Flashcard 53: What is the length of a 2D array row array[0]?

Answer: array[0].length. Returns number of columns in the specified row.

Flashcard 54: What will array.length return for a 4x6 2D array?

Answer:

1. Length property returns number of rows in the array.

Flashcard 55: Which method accesses the element at row 2, column 1?

Answer: array[2][1];. First index specifies row, second index specifies column.

Flashcard 56: How do you initialize a 2D array with specific String values?

Answer: String[][] array = {{"a", "b"}, {"c", "d"}};. Initializer syntax with String literals in nested structure.

Flashcard 57: How do you declare a 2D array in Java?

Answer: int[][] arrayName;. Declaration syntax uses double brackets for 2D array type.

Flashcard 58: How do you declare a char 2D array?

Answer: char[][] array;. Declaration syntax for character data type in 2D format.

Flashcard 59: What is the syntax to assign 'A' to the first element of a 2D char array?

Answer: array[0][0] = 'A';. Assignment uses array indexing with character literal value.

Flashcard 60: What is a jagged array?

Answer: A 2D array where rows have different lengths. Each row can have different number of columns.

Flashcard 61: Identify the method to get the number of columns in the first row.

Answer: array[0].length. Accesses the length property of the first row array.

Flashcard 62: How do you check if a 2D array is empty?

Answer: Check if array.length == 0 or array[0].length == 0. Check both row count and first row column count.

Flashcard 63: How do you update the element at row 1, column 2 to 10?

Answer: array[1][2] = 10;. Assignment syntax uses array notation with row and column indices.

Flashcard 64: Which keyword is used to create a new 2D array in Java?

Answer: new. Required keyword for dynamic memory allocation in Java.

Flashcard 65: How do you declare a 2D array to store Strings?

Answer: String[][] array;. Declaration syntax for String object references in 2D array.

Flashcard 66: How do you initialize a 2D array with 2 rows and 3 columns?

Answer: int[][] array = new int[2][3];. Specifies exact dimensions during array creation.