Arrays Mostafa Abdallah Engmostafamuficyahoo com Agenda What Is
Arrays Mostafa Abdallah Eng_mostafa_mufic@yahoo. com
Agenda • • What Is an Array. Initializing and using an Array. Using Arrays in Methods. Two-dimensional Arrays.
Arrays 6 -3
Arrays • Array is used to store a collection of data of the same type. • Instead of declaring individual variables, such as number 0, number 1, . . . , and number 99. • You declare one array variable such as numbers and use numbers[0], numbers[1], and. . . , numbers[99] variables. to represent individual 6 -4
Arrays, cont. 6 -5
Arrays, cont. • Declaring Array – data. Type [] array. Ref. Var; • Example: – int[] array. Name; • Creating Arrays − array. Ref. Var = new data. Type[array. Size]; • Example: − array. Name = new int[5]; 6 -6
Arrays, cont. • When we need to access the array we can do so directly as in: Ex: - array. Name[2]=5; - for (int i=0; i<5; i++) { System. out. println( array. Name[i] ); } // end for 6 -7
Example double[] my. List = new double[10]; for (int i = 1; i < my. List. length; i++) { my. List[i]=i; } for (int i = 1; i < my. List. length; i++) { System. out. println(my. List[i]); } 6 -8
Array Initializers • Declaring, creating, initializing in one step: double [] my. List = {1. 9, 2. 9, 3. 4, 3. 5}; • This shorthand syntax must be in one statement and it’s equivalent to the following statements: double [] my. List = new double[4]; my. List[0] = 1. 9; my. List[1] = 2. 9; my. List[2] = 3. 4; my. List[3] = 3. 5; 6 -9
Using Arrays in Methods 6 -10
Passing Arrays to Methods public static void print. Array(int[] array) { for (int i = 0; i < array. length; i++) { System. out. print(array[i] + " "); } } Invoke the method int[] list = {3, 1, 2, 6, 4, 2}; print. Array(list); 6 -11
Returning an Array from a Method public static int[] reverse(int[] list) { int[] result = new int[list. length]; for (int i = 0, j = result. length - 1; i < list. length; i++, j--) { result[j] = list[i]; } return result; } int[] list 1 = {1, 2, 3, 4, 5, 6}; int[] list 2 = reverse(list 1); 6 -12
Two-dimensional Arrays 6 -13
Two-dimensional Arrays // Declare array ref var data. Type[][] ref. Var; // Create array and assign its reference to variable ref. Var = new data. Type[10]; // Combine declaration and creation in one statement data. Type[][] ref. Var = new data. Type[10]; 6 -14
Two-dimensional Arrays, cont. int[][] matrix = new int[10]; or int matrix[][] = new int[10]; matrix[0][0] = 3; for (int i = 0; i < matrix. length; i++) for (int j = 0; j < matrix[i]. length; j++) matrix[i][j] = (int)(Math. random() * 1000); 6 -15
Two-dimensional Arrays, cont. • You can also use an array initializer to declare, create and initialize a two-dimensional array. For example, int[][] array = { {1, 2, 3}, {4, 5, 6}, Same as {7, 8, 9}, {10, 11, 12} }; int[][] array = new int[4][3]; array[0][0] = 1; array[0][1] = 2; array[0][2] = 3; array[1][0] = 4; array[1][1] = 5; array[1][2] = 6; array[2][0] = 7; array[2][1] = 8; array[2][2] = 9; array[3][0] = 10; array[3][1] = 11; array[3][2] = 12; 6 -16
Lengths of Two-dimensional Arrays int[][] x = new int[3][4]; 6 -17
Lengths of Two-dimensional Arrays, cont. int[][] array = { {1, 2, 3}, {4, 5, 6}, {7, 8, 9}, {10, 11, 12} }; array. length array[0]. length array[1]. length array[2]. length array[3]. length array[4]. length Array. Index. Out. Of. Bounds. Exception 6 -18
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