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Arrays. Rows and rows and rows. Image courtesy of http ://www.flickr.com/photos/andrewmorrell/54069752/sizes/z/in/photostream/. Arrays. A contiguous collection of cells Cells are also known as: elements, items, entries, slots Each cell contains the same “type” of item
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Arrays Rows and rows and rows Image courtesy of http://www.flickr.com/photos/andrewmorrell/54069752/sizes/z/in/photostream/
Arrays • A contiguous collection of cells • Cells are also known as: elements, items, entries, slots • Each cell contains the same “type” of item • The number of cells in an array will never change! • Cells are given names (in a sense) • Indices (subscripts) beginning at 0 A cell can be thought of as a box that contains data of some kind. An array is a bunch of boxes
Arrays • When using arrays • First: create the array itself. Must specify size! • Second: place data into each box • Third: relax • Syntax for declaring an array variable • ClassName [] variableName; • Syntax for creating an array • new ClassName [ ArraySize ]
Arrays • Syntax for accessing an element of the array (opening a box and holding the contents) • arrayVariable[ index ] • The index must be between 0 and the length of the array – 1. • Syntax for replacing an element of the array (opening a box and replacing the contents) • arrayVariable[ index ] = someExpression ; • The index must be between 0 and the length of the array -1 • Type conformance rules are still followed • Syntax for finding the length of an array • arrayVariable.length
Array Example int[] numbers; int number; numbers = new int[3]; numbers[0] = 1; numbers[1] = -1; numbers[2] = numbers[0]+numbers[1]; numbers[numbers[2]] = numbers[1]; number = numbers[1]; numbers
Array Example int[] numbers; int number; numbers = new int[3]; numbers[0] = 1; numbers[1] = 3; numbers[2] = numbers[1]-numbers[0]; numbers[numbers[2]] = numbers[1]; number = numbers[1]; numbers
Array Example int[] numbers; int number; numbers = new int[3]; numbers[0] = 1; numbers[1] = 3; numbers[2] = numbers[1]-numbers[0]; numbers[numbers[2]] = numbers[1]; number = numbers[1]; numbers
Array Example int[] numbers; int number; numbers = new int[3]; numbers[0] = 1; numbers[1] = 3; numbers[2] = numbers[1]-numbers[0]; numbers[numbers[2]] = numbers[1]; number = numbers[1]; numbers
Array Example int[] numbers; int number; numbers = new int[3]; numbers[0] = 1; numbers[1] = 3; numbers[2] = numbers[1]-numbers[0]; numbers[numbers[2]] = numbers[1]; number = numbers[1]; numbers
Array Example int[] numbers; int number; numbers = new int[3]; numbers[0] = 1; numbers[1] = 3; numbers[2] = numbers[1]-numbers[0]; numbers[numbers[2]] = numbers[1]; number = numbers[1]; numbers
Array Examples Rectangle[] rects = new Rectangle[4]; rects[0] = new Rectangle(10, 20, 30, 40); rects[1] = new Rectangle(0, 0, 100, 100); rects[2] = rects[1]; Rectangle oneRect = new Rectangle(10, 10, 10, 10); rects[3] = oneRect; oneRect = rects[0]; char[] bunchOfChars = new char[20]; bunchOfChars[0] = ‘A’; bunchOfChars[bunchOfChars.length-1] = ‘?’;
Arrays • Can be passed to functions and returned from functions • Problem: write a method that takes an array of Rectangle objects and sets all of their colors to red private void colorAllRed( Rectangle[] rects ) { for(inti=0; i<rects.length; i++) { rects[i].setBackground( Color.red ); } } Rectangle[] someRects; someRects = new Rectangle[3]; someRects[0] = new Rectangle(0,0,5,5); someRects[1] = new Rectangle(6,6,8,8); someRects[2] = new Rectangle(10,10,10,10); colorAllRed( someRects );
Initializing arrays • Arrays can be filled with data when declared int[] arr = {10, 100, 1000}; Oval[] circles = { new Oval(1,1,1,1), new Oval(2,2,2,2) }; int[] arr = new int[3]; arr[0] = 10; arr[1] = 100; arr[2] = 1000; Oval[] circles = new Oval[2]; circle[0] = new Oval(1,1,1,1); circle[1] = new Oval(2,2,2,2);
Examples • Write a program to sum the elements in an array of doubles. public double sum(double[] values) { double result = 0; for(int i=0; i<values.length; i++) { result += values[i]; } return result; }
Examples • Write a function that accepts an array of doubles named A and a double named V. The function returns the index of the first occurrence of V in A or -1 if X is not in A. public int indexOf(double[] a, double v) { for(int i=0; i<a.length; i++) { if(v == a[i]) return i; } return -1; }
Examples • Write a function that accepts an array of doubles named A and a double named V. The function returns an array of all elements of A that are greater than V. public double[] greaterThan(double[] a, double v) { int count=0; for(int i=0; i<a.length; i++) { if(a[i] > v) count++; } double result = new double[count]; int resultIndex = 0; for(int i=0; i<a.length; i++) { if(a[i] > v) result[resultIndex++] = a[i]; } return result; }
Examples • Write a function that accepts an array of ints and “shuffles” them into a random order. • Do the following 2*n times, where n is the number of elements in the array • select to random indices into the array and swap the elements in the array • public void shuffle(int[] values) { • for(int i=0; i<values.length*2; i++) { • int ranIndex1 = (int)(Math.random()*values.length); • int ranIndex2 = (int)(Math.random()*values.length); • int tmp = values[ranIndex1]; • values[randIndex1] = values[ranIndex2]; • values[randIndex2] = tmp; • } • } int[] data = {1,2,3,4,5}; shuffle(data);
Examples • Write a function that accepts an array of ints and returns the smallest index of the smallest value • /* @pre = values.length >= 1 */ • public int findMin(int[] values) { • int minIndex = 0; • for(int i=1; i<values.length; i++) { • if(values[i] < values[minIndex]) minIndex = i; • } • return minIndex; • }
Tic Tac Toe • Write a TicTacToeModel using arrays!
